g62-encyclopaedia-of-pests-and-natural-enemies-in-field-crops

Encyclopaedia ofpests and natural enemiesin field crops

ContentsContentsPageIntroduction 2Index 3Identification of larvae 11Pest thresholds: quick reference 12Pests:Beetles 16Bugs and aphids 42Flies, thrips and sawflies 80Moths and butterflies 126Nematodes 150Other pests 162Natural enemies:Introduction 172IntroductionIntegrated pest managementManaging pests while encouraging and supporting beneficial insects is anessential part of an integrated pest management strategy and is a keycomponent of sustainable crop production.The number of available insecticides is declining, so it is increasingly importantto use them only when absolutely necessary to safeguard their longevity andminimise the risk of the development of resistance. The Sustainable UseDirective (2009/128/EC) lists a number of provisions aimed at achieving thesustainable use of pesticides, including the promotion of low input regimes,such as integrated pest management.Effective pest control:Assess therisk ofinfestationMinimiserisk byculturalmeansMaximise theeffects ofnaturalenemiesOnly usepesticides ifeconomicallyjustifiedThis publicationBuilding on the success of the HGCA/BASF Encyclopaedia of arable weeds andthe HGCA/BASF Encyclopaedia of cereal diseases, the three crop divisions ofthe Agriculture and Horticulture Development Board have worked together onthis new encyclopaedia providing information on the identification andmanagement of pests and natural enemies. The latest information has beenprovided by experts from ADAS, Game and Wildlife Conservation Trust,Warwick Crop Centre, PGRO and BBRO.Beetles 175Bugs 181Centipedes 184Flies 185Lacewings 191Sawflies, wasps, ants and bees 192Spiders and mites 1971Encyclopaedia of pests and natural enemies in field cropsEncyclopaedia of pests and natural enemies in field crops2

IndexIndexAAcrolepiopsis assectella (leek moth) 139Acyrthosiphon pisum (pea aphid) 61Black bean aphid (Aphis fabae) 45Boettgerilla spp. (keeled slug) 163Agriotes spp. (wireworms) 33Brassica leaf miner (Scaptomyza flava) 85Agrotis segetum (cutworms) 129Brassica pod midge (Dasineura brassicae) 87Aleocharinae 178Brevicoryne brassicae (mealy cabbage aphid) 59Aleyrodes proletella (cabbage whitefly) 49Bruchid beetle (Bruchus rufimanus) 17Allium leaf miner (Phytomyza gymnostoma) 123Bruchus rufimanus (bruchid beetle) 17Ants (Formicidae) 193Buckthorn–potato aphid (Aphis nasturtii) 47Aphids 42Bugs (Hemiptera) 42, 181Aphis fabae (black bean aphid) 45Aphis nasturtii (buckthorn–potato aphid) 47Arion spp. (garden slug) 163CButterflies (Lepidoptera) 126Cabbage aphid (Brevicoryne brassicae) 59Cabbage leaf miner (Phytomyza rufipes) 85Assassin bugs (Reduviidae) 183Cabbage moth (Mamestra brassicae) 127Athalia rosae (turnip sawfly) 117Cabbage root fly (Delia radicum) 89Atomaria linearis (pygmy beetle) 40Cabbage seed weevil (Ceutorhynchus assimilis) 19BAutographa gamma (silver Y moth) 143Balloon and dagger flies (Empididae) 187Barley yellow dwarf virus (BYDV) 43, 53Cabbage stem flea beetle (Psylliodes chrysocephala) 21Cabbage stem weevil (Ceutorhynchus quadridens) 23Cabbage whitefly (Aleyrodes proletella) 49Bean leaf roll virus (BLRV) 45, 61Caliothrips fasciatus (thrips) 111Bean seed flies (Delia platura and Delia florilega) 81Carrot fly (Psila rosae) 93Bean yellow mosaic virus (BYMV) 45Carrot motley dwarf disease 75Beet chlorosis virus (BChV) 65Cauliflower mosaic virus (CaMV) 59, 65Beet cyst nematode (Heterodera schachtii) 151Cavariella aegopodii (willow–carrot aphid) 75Beet leaf miner (Pegomya hyoscyami) 83Centipedes (Chilopoda) 184Beet mild yellowing virus (BMYV) 65, 69Cephus pygmaeus (cereal stem sawfly) 124Beet yellows virus (BYV) 45, 65, 69Cereal cyst nematode (Heterodera avenae) 159Beetles (Coleoptera) 16, 175Cereal ground beetle (Zabrus tenebrioides) 37Beneficial insects 172Cereal leaf beetle (Oulema melanopa) 37Bird cherry–oat aphid (Rhopalosiphum padi) 43Cereal stem sawfly (Cephus pygmaeus) 1243Encyclopaedia of pests and natural enemies in arable and field cropsEncyclopaedia of pests and natural enemies in arable and field crops4

IndexDCeutorhynchus assimilis (cabbage seed weevil) 19Ceutorhynchus pictarsis (rape winter stem weevil) 31Ceutorhynchus quadridens (cabbage stem weevil) 23Chafer grubs (Melolontha melolontha) 38Chlorops pumilionis (gout fly) 97Click beetles (Elateridae) 33Cnephasia asseclana (flax tortrix moth) 147Coleoptera (beetles) 16, 175Colorado beetle (Leptinotarsa decemlineata) 38Contarinia nasturtii (swede midge) 109Contarinia pisi (pea midge) 105Contarinia tritici (yellow wheat blossom midge) 124Crane flies (Tipula spp.) 99Currant–lettuce aphid (Nasonovia ribisnigri) 51Cutworms (Noctuid moths) 129Cydia nigricana (pea moth) 141Damsel bugs (Nabidae) 182Dance flies (Hybotidae) 188Dasineura brassicae (brassica pod midge) 87Delia antiqua (onion fly) 101Delia coarctata (wheat bulb fly) 119Delia spp. (bean seed flies) 81Delia radicum (cabbage root fly) 89Deroceras spp. (grey field slug) 163Diamond-back moth (Plutella xylostella) 131Diptera (flies) 80, 185Ditylenchus dipsaci (stem nematode) 157Docking disorder 153Dung flies (Scathophagidae) 1885 Encyclopaedia of pests and natural enemies in field cropsIndexEFGHKEvergestis forficalis (garden pebble moth) 133Fanging 153Field thrips (Thrips angusticeps) 111Flax tortrix moth (Cnephasia asseclana) 147Flea beetles 21, 39Flies (Diptera) 80, 185Flower and pirate bugs (Anthocoridae) 181Free-living nematodes 153Frit fly (Oscinella frit) 95Gall midges (Cecidomyiidae) 189Garden pebble moth (Evergestis forficalis) 133Garden slug (Arion spp.) 163Ghost moth (Hepialus humuli) 135Globodera spp. (potato cyst nematode) 155Gout fly (Chlorops pumilionis) 97Grain aphid (Sitobion avenae) 53Grey field slug (Deroceras spp.) 163Ground beetles (Carabidae) 175Haplodiplosis marginata (saddle gall midge) 107Helophorus nubilus (wheat shoot beetle) 40Hemiptera (bugs) 42, 181Hepialus humuli (ghost moth) 135Hepialus lupulinus (swift moth) 135Heterodera avenae (cereal cyst nematode) 159Heterodera goettingiana (pea cyst nematode) 160Heterodera schachtii (beet cyst nematode) 151Hoverflies (Syrphidae) 190Hymenoptera (sawflies, wasps, ants and bees) 80, 192Kakothrips pisivorus (pea thrips) 111Encyclopaedia of pests and natural enemies in field crops6

IndexIndexLKeeled slug (Milax, Tandonia and Boettgerilla spp.) 163Korscheltellus lupulinus (swift moth) 135Lacewings (Neuroptera) 191Ladybirds (Coccinellidae) 180ONoctuid moths (cutworms) 129Onion fly (Delia antiqua) 101Onion thrips (Thrips tabaci) 111Opomyza florum (yellow cereal fly) 121Large white butterfly (Pieris brassicae) 137Orange wheat blossom midge (Sitodiplosis mosellana) 103Leatherjackets (Tipula spp.) 99Oscinella frit (frit fly) 95Leek moth (Acrolepiopsis assectella) 139Lepidoptera (moths and butterflies) 126Leptinotarsa decemlineata (Colorado beetle) 38POulema melanopa (cereal leaf beetle) 37Parasitic wasps 194Parasitoids 194Lettuce root aphid (Pemphigus bursarius) 57Paratrichodorus spp. (stubby root nematodes) 153Longidorus spp. (needle nematodes) 153Parsnip yellow fleck virus (PYFV) 75Long-legged flies (Dolichopodidae) 186Pea and bean weevil (Sitona lineatus) 25MLygus rugulipennis (tarnished plant bug) 73Macrosiphum euphorbiae (potato aphid) 69Mamestra brassicae (cabbage moth) 127Pea aphid (Acyrthosiphon pisum) 61Pea cyst nematode (Heterodera goettingiana) 160Pea enation mosaic virus (PEMV) 45, 61Mealy cabbage aphid (Brevicoryne brassicae) 59Pea midge (Contarinia pisi) 105Meligethes spp. (pollen beetle) 27Pea moth (Cydia nigricana) 141Meloidogyne spp. (root knot nematode) 160Pea seed-borne mosaic virus (PSbMV) 61Melolontha melolontha (chafer grubs) 38Pea thrips (Kakothrips pisivorus) 111Metopolophium dirhodum (rose–grain aphid) 71Peach–potato aphid (Myzus persicae) 65Milax spp. (keeled slug) 163Pegomya hyoscyami (beet leaf miner) 83Millipedes 167Pemphigus bursarius (lettuce root aphid) 57Mites 170, 198Phytomyza gymnostoma (allium leaf miner) 123Moths (Lepidoptera) 126Phytomyza rufipes (cabbage leaf miner) 85NMyzus persicae (peach–potato aphid) 65Nasonovia ribisnigri (currant–lettuce aphid) 51Natural enemies 172Pieris brassicae (large white butterfly) 137Pieris rapae (small white butterfly) 145Plutella xylostella (diamond-back moth) 131Needle nematodes (Longidorus spp.) 153Pollen beetle (Meligethes spp.) 27Nematodes (Nematoda) 150Potato aphid (Macrosiphum euphorbiae) 697Encyclopaedia of pests and natural enemies in field cropsEncyclopaedia of pests and natural enemies in field crops8

IndexRSPotato cyst nematode (Globodera spp.) 155Potato leafhoppers 77Potato leaf roll virus (PLRV) 65, 69Potato virus A (PVA) 47, 65Potato virus Y (PVY) 47, 65, 69Psila rosae (carrot fly) 93Psylliodes chrysocephala (cabbage stem flea beetle) 21Pygmy beetle (Atomaria linearis) 40Rape winter stem weevil (Ceutorhynchus pictarsis) 31Rhopalosiphum padi (bird cherry–oat aphid) 43Robber flies (Asilidae) 185Root knot nematode (Meloidogyne spp.) 160Rose–grain aphid (Metopolophium dirhodum) 71Rove beetles (Staphylinidae) 177Saddle gall midge (Haplodiplosis marginata) 107Sawflies (Hymenoptera) 80, 192Scaptomyza flava (brassica leaf miner) 85Silver Y moth (Autographa gamma) 143Sitobion avenae (grain aphid) 53Sitodiplosis mosellana (orange wheat blossom midge) 103Sitona lineatus (pea and bean weevil) 25Slugs 163Small white butterfly (Pieris rapae) 145Soil pest complex 167Soldier beetles (Cantharidae) 179Spiders and mites (Arachnida) 197Spraing 153Springtails 167, 169Stem nematode (Ditylenchus dipsaci) 157IndexTWYZStubby root nematodes 153Swede midge (Contarinia nasturtii) 109Swift moth (Korscheltellus lupulinus) 135Symphylids 167Tandonia spp. (keeled slug) 163Tarnished plant bug (Lygus rugulipennis) 73Tetranychus urticae (two-spotted spider mites) 170Thrips (Thysanoptera) 80, 111Thrips angusticeps (field thrips) 111Thrips tabaci (onion thrips) 111Thysanoptera (thrips) 80, 111Tipula spp. (leatherjackets) 99Tobacco rattle virus (TRV) 153Trichodorus spp. (stubby root nematodes) 153Turnip mosaic virus (TuMV) 59Turnip moth (Agrotis segetum) 129Turnip sawfly (Athalia rosae) 117Turnip yellows virus (TuYV) 65Two-spotted spider mites (Tetranychus urticae) 170Wasps (Hymenoptera) 192Wheat bulb fly (Delia coarctata) 119Wheat shoot beetle (Helophorus nubilus) 40Wheat stem sawfly (Cephus pygmaeus) 124Willow–carrot aphid (Cavariella aegopodii) 75Wireworms (Agriotes spp.) 33Yellow cereal fly (Opomyza florum) 121Yellow wheat blossom midge (Contarinia tritici) 124Zabrus tenebrioides (cereal ground beetle) 379 Encyclopaedia of pests and natural enemies in field cropsEncyclopaedia of pests and natural enemies in field crops10

Identification of larvaeBeetleWeevilFly11Distinct headThree pairs of legs on thoraxDistinct headMoth/butterflyToughenedheadNo legsIndistinct headThree pairs of legson thoraxSawflySmooth headcapsule withdistinct smallblack eyesNo legsThree pairs of legs on thoraxFirst two abdominalsegments are leglessFive or fewer pairs of prolegs on abdomenSix or more pairs of prolegs on abdomenEncyclopaedia of pests and natural enemies in field cropsPest thresholds: quick referenceIntegrated pest management involves using thresholds as the basis for controlstrategies:– Identify the pest– Assess pest numbers on a field-by-field basis– Look up pest thresholds – Reassess if treatment is delayedCerealsWireworms(p. 33)Summer aphids(p. 54 and p. 71)Frit fly(p. 95)Gout fly(p. 97)Leatherjackets(p. 99)Orange wheatblossom midge(p. 103)Wheat bulb fly(p. 119)Slugs(p. 163)A seed treatment is justified if there are more than750,000 wireworms per hectareBefore GS61: half of tillers infestedGS61 to two weeks before end of grain filling: two-thirdsof tillers infestedMore than 10% of plants damaged soon after full cropemergenceWinter crops at GS12:– Eggs found on more than half of plantsSpring cereals, prior to cultivation:– 50 leatherjackets per m 2– 5 leatherjackets in 12 pipes– 5 leatherjackets per metre of rowPheromone traps (at GS45):– 30 or more midges: General risk to crops in the followingweek– More than 120 midges: Very high risk. Treat wheat cropsin surrounding fields at GS53–59Crop monitoring (at GS53–59):– Feed crops: 1 midge per 3 ears– Milling/seed crops: 1 midge per 6 earsEgg numbers in mid-September:– Fewer than 100 eggs/m 2 : Seed treatment justified inspring-sown cereals– 100–249 eggs/m 2 : Seed treatment justified in late-sownand spring-sown cereals– 250–500 eggs/m 2 : Seed treatment justified in late-sownand spring-sown cereals; egg-hatch spray may be justified– More than 500 eggs/m 2 : Egg-hatch spray justified in earlysown cereals; seed treatment and egg-hatch sprayjustified in late-sown and spring-sown cerealsSlugs per refuge trap, prior to cultivation:– Winter cereals: 4– Spring cereals: 1Encyclopaedia of pests and natural enemies in field crops12

Pest thresholds: quick referencePest thresholds: quick referenceOilseed rapeField beansCabbage seedweevil(p. 19)Cabbage stemflea beetle(p. 21)Weevils per plant during flowering:– Northern UK: 0.5– Elsewhere: 1Adult feeding thresholds:– >25% leaf area eaten at the cotyledon–2 leaf stage– >50% leaf area eaten at the 3–4 leaf stage– The crop is growing more slowly than it is beingconsumedBruchid beetle(p. 17)Pea and beanweevil(p. 25)Black beanaphid(p. 45)Treatment should be applied when, during flowering:– Adults have been found in the crop– The temperature has reached 20°C on two consecutivedays– Beans have developed the first pods on the lowest trussesSpring field beans:– An average of 30 or more weevils on any one recordingdayPollen beetle(p. 27)Mealy cabbageaphid(p. 59)Leatherjackets(p. 99)Slugs(p. 163)Thresholds for control of larvae:Yellow water trap:– >35 beetles/trap caught in total between earlySeptember and the end of OctoberPlant dissection:– >2 larvae per plant– 50% of petioles damagedBeetles per plant at the green to yellow bud stage:– If there are fewer than 30 plants/m 2 : 25– If there are 30–50 plants/m 2 : 18– If there are 50–70 plants/m 2 : 11– If there are more than 70 plants/m 2 : 7% of plants infested before petal fall:– Winter oilseed rape: more than 13%– Spring oilseed rape: more than 4%Prior to cultivation:– More than 50 leatherjackets per m 2– More than 5 leatherjackets in 12 pipes– More than 5 leatherjackets per metre of rowSlugs per refuge trap, prior to cultivation:– In cereal crops: 4– In cereal stubble: 1Slugs (p. 163)PeasPea and beanweevil(p. 25)Pea aphid(p. 61)Pea midge(p. 105)Pea moth(p. 141)Early flowering until pod formation:– 10% of plants infested: Immediate treatment is justified– 5% of plants infested: Treatment can help prevent virusinfection1 slug per refuge trap, prior to cultivationSpring-sown peas:– An average of 30 or more weevils on any one recordingday% plants infested, May to July:– Combining peas: 20% or more– Vining peas: 15% or moreIf more than 500 midges are caught on one trap (placedby the third week of May), susceptible pea crops in thenear vicinity should be examinedDry harvested peas for human consumption:– 10 or more moths caught in traps (placed by the middleof May and examined at two-day intervals) on twoconsecutive occasionsVining peas:Traps are just used to determine if moths are present.Growers should be guided by the factory fieldsman aseven very small infestations can lead to rejectionVining peas:– Cumulative catch exceeds 50 moths by the first podstage (GS204)Silver Y moth(p. 143)Slugs (p. 163)1 slug per refuge trap, prior to cultivation13Encyclopaedia of pests and natural enemies in field cropsEncyclopaedia of pests and natural enemies in field crops14

Pest thresholds: quick referencePotatoesWireworms(p. 33)Potato cystnematode(p. 155)The presence of even a single wireworm in twenty 10 cmdiameter soil cores can represent a significant risk in thefollowing cropEggs per gram of soil:– 1–10: Nematicide use recommended– 10–20: Nematicide treatment highly recommended– >20: Take into account all factors and, if appropriate,consider other groundSugar beetBlack beanaphid(p. 45)Green aphids(p. 65)Beet leaf miner(p. 83)Silver Y moth(p. 143)Beet cystnematode(p. 151)Free-livingnematodes(p. 153)Slugs(p. 163)Treatment is only justified on backward or stressed cropswith more than 100 aphids per plant (averaged across thefield)Apply a foliar insecticide when one green wingless aphidper four plants is found. This increases to one greenwingless aphid per plant once at the 12 leaf stage.Treat if the number of eggs and larvae exceed the squareof the number of true leaves; for example, if a plant withfour true leaves has a population of 16 or more eggs andlarvaeThe threshold is five caterpillars per plantThresholds vary widely across Europe. In the UK, latestresults show an economic benefit from using BCNtolerantvarieties above two eggs and larvae per gram ofsoilSevere symptoms often occur in soils with Trichodoruspopulations of more than 1,000/litre of soil or Longidoruspopulations of more than 100/litre of soil1 slug per refuge trap, prior to cultivation15Encyclopaedia of pests and natural enemies in field crops

Pests:Beetles

Contents – Pests: BeetlesSpeciesPageBruchid beetle (Bruchus rufimanus) 17Cabbage seed weevil (Ceutorhynchus assimilis) 19Cabbage stem flea beetle (Psylliodes chrysocephala) 21Cabbage stem weevil (Ceutorhynchus quadridens) 23Pea and bean weevil (Sitona lineatus) 25Pollen beetle (Meligethes spp.) 27Rape winter stem weevil (Ceutorhynchus pictarsis) 31Wireworms (Agriotes spp.) 33Minor and/or emerging pests 37Cereal ground beetle (Zabrus tenebrioides) 37Cereal leaf beetle (Oulema melanopa) 37Chafer grubs (Melolontha melolontha) 38Colorado beetle (Leptinotarsa decemlineata) 38Other flea beetles 39Pygmy beetle (Atomaria linearis) 40Wheat shoot beetle (Helophorus nubilus) 40Further information 41

Beetles (Coleoptera)Beetles occur in all types of habitats and are among the commonest insects onfarmland. A few beetle species are crop pests but the majority are harmless, whilesome are important predators of crop pests (see page 175).Life cycleBeetle young (larvae) do not lookAdultanything like the adults. Theirouter skin cannot grow and so Pupamust be shed in a series ofmoults as the beetle larva grows.The developmental stagesbetween each moult are called‘instars’. When the larva is fullygrown, it moults again, revealing aFully grown larvapupa. This is a non-feeding stage,inside which the larval body is broken down and reassembled in the adult form.EggsLarvaDefining featuresAdult beetles have a defined head andthorax and a distinct pair of hard wingcases covering the rest of their bodies,which meet in a line down the middle.Hard wingcasesAntennaeBiting mouthpartsHeadThoraxAbdomenBeetle larvae have hardened, oftendark, heads with biting mouthparts. Theyhave three pairs of legs and spiracles(the openings of the respiratory system)along the sides of the body.Weevils are a type of beetle. The adultshave a snout with angular antennae. Thelarvae do not have legs (see page 11).BitingmouthpartsLegsSpiraclesSnoutElbowedantennaeHeadThoraxBiting mouthpartsAbdomenHeadThoraxHard wing casesAbdomenPests: Beetles16

Bruchid beetle (Bruchus rufimanus)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeas✔ Field beansSugar beetLettuceLife cycle1234ImportanceIn field beans, seeds damaged by the bruchid beetlereduce the value of the crop for human consumption,export trade or for seed.In broad beans, the presence of the damage or thelarvae makes them unacceptable for processing andmay lead to rejection of the crop.Risk factorsThe pest is common in the south of the UK, up toYorkshire.Risk of economically damaging infestations is greaterwhere the pest occurred in previous crops.The adults fly into crops if the temperature is 15–20°Cfor several consecutive days.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12Adults overwinter in hedgerows or other dense,shrubby habitats.Adults fly into flowering bean crops when thetemperature reaches 15–20°C.Eggs are laid on pods after adults have fed onpollen for two weeks and the temperature hasexceeded 20°C.Larvae feed on the seeds before pupating withinthe seed. Pupation can occur in the field or instorage. Adults eat their way out of the seed.In field beans, the larvae pupate at the same time asthe seed matures and dries. Pupation and adultemergence often occur in storage, especially if themoisture content of the seed is high; however, thispest does not multiply in stored produce.34© PGRO1Adult bruchid beetlewith bean seedsBruchid beetle (Bruchus rufimanus)Identification and symptomsThe adult beetle is 3.5–4.5 mm long and oval. It isblack or dark brown, with small, grey flecks along thewing cases. The base of the antennae and the frontlegs are a reddish colour. The wing case does notextend to cover the abdomen completely and the hindlegs appear longer than the first two pairs of legs.Yellowish, cigar-shaped eggs, around 0.5 mm long, arelaid singly or in small groups on young seed pods.Pods that are 2–5 cm long and on the lower third ofthe plant seem to be preferred for egg laying.The white fleshy larvae have a light brown head andthree pairs of legs on the forward three segments.Upon hatching, they bore directly into the pod to theseeds and at maturity are 3–4 mm long.In field beans, damage is characterised by a circularemergence hole in the seed where the adult beetlehas bitten its way through the seed coat. In broadbeans, the entry hole of the newly hatched larvae canbe seen as a small hole or cut in the seed coat of theshelled bean, which may darken after vining. Cuttingthe beans open may reveal the immature larvae.MonitoringCrops should be examined for adults during flowering. This can be done by tappingthe flowering stems into the hand or a shallow tray.ThresholdsTreatment should be applied when adults have been found in the crop, thetemperature has reached 20°C on two consecutive days and beans have developedthe first pods on the lowest trusses.Bruchid beetle spray forecasts are available from Syngenta:www3.syngenta.com/country/uk/en/AgronomyTools/Pages/BruchidCast.aspxNon-chemical controlThe parasitic wasp, Triaspis luteipes, attacks the beetle larvae. Small emergenceholes in the seeds may be due to this natural enemy.Insecticide resistanceNone known.© PGROBruchid beetle eggs© Jon OakleyBruchid beetle anddamage17Pests: BeetlesPests: Beetles18

Cabbage seed weevil (Ceutorhynchus assimilis)Cabbage seed weevil (Ceutorhynchus assimilis)Crops affectedCereals✔ OilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceCabbage seed weevils lay their eggs within the podsand the larvae feed on the developing seed.Exit holes in the pods, created by seed weevil larvaereturning to the soil to pupate, provide access forbrassica pod midge adults to lay their eggs (seepage 87). Yield losses from pod midge are potentiallygreater than direct losses from seed weevil.Risk factorsCrops in the north of the UK tend to be at a greaterrisk.Identification and symptomsThe adult is a small (2–3 mm) lead-grey to black weevilwith a long snout.Eggs are laid singly in young pods.Larvae are plump, white, with a definite brown headcapsule and no legs. At maturity, the larvae bore anexit hole in the pod and fall to the soil to pupate.A brown scar, usually resulting in a kink in the pod,indicates where the pod has been punctured for egglaying. The larva feeds within the pod, usuallyconsuming approximately 25% of the total seeds. Aneat, circular hole indicates where the larva hasescaped the pod to pupate.© ADASCabbage seed weevilon oilseed rape flower© Dewar Crop ProtectionLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 4MonitoringCheck the crop during flowering for the presence ofthe weevil. They are readily visible on floweringracemes on sunny days.1 Adults overwinter in woods and hedgerows.234Adults migrate into crops during flowering andlay eggs in pods.Larvae feed within the pod before burrowing outto pupate in the soil.Adults emerge in August and hibernate in noncropsituations. If further brassica crops arepresent, they may continue to feed beforehibernating.3© ADASCabbage seed weevilThresholdsNorthern UK: 0.5 per plantElsewhere: 1 per plantNon-chemical controlThere are a number of parasitoid species that attackthis pest, including parasitoids of egg, larval and adultstages. Encouraging their presence can help control.Insecticide resistanceNone known.Cabbage seed weevillarva on oilseed rape19Pests: BeetlesPests: Beetles20

Cabbage stem flea beetle (Psylliodes chrysocephala)Cabbage stem flea beetle (Psylliodes chrysocephala)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceCabbage stem flea beetle is a major pest of oilseedrape. Originally a problem in East Anglia, it now coversEngland and Wales and is spreading in Scotland.Large numbers of adults feeding in the autumn can killplants, occasionally resulting in total crop failure. Larvalfeeding in the stems and petioles reduces vigour andcan cause severe damage, which may lead to stuntingor plant death.Larvae may feed within the stems of vegetablebrassicas, such as spring cabbage and kale, duringautumn and winter but it is an incidental pest.Risk factorsEarly sown crops are more susceptible to attack.A warm autumn will favour egg laying and early hatchof larvae, coinciding with smaller, more vulnerable plants.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec561 Adults emerge and feed on foliage.2 Adults ‘rest’ in moist, sheltered places.3 Adults move into crop, mate and eat leavesfor a week or so.4 Eggs are laid at the base of the plant, if mild.Identification and symptomsAdults are 3–5 mm long, metallic blue-black or lightbrown and are often seen crawling over trailer loads ofseed at harvest. They have long antennae, large hindlegs and jump when disturbed. The larvae are whitewith numerous, very small, dark spots on the back, ablack head and tail and three pairs of dark legs. Whenfully grown, they can reach 6 mm in length.71256734 5Eggs hatch, if mild, andlarvae feed in petioles.Larvae feed on main stembehind growing point.Larvae pupate in soil.© Dewar Crop ProtectionCabbage stem flea beetlecreating shot-holingsymptomsAdult feeding can be seen as characteristic shot-holing of the leaves. Plants infestedwith larvae lose vigour, becoming stunted, and die if the infestation is severe.MonitoringA quick look in grain trailers will give an indication of thenumber of beetles available to invade crops. Pestpressure can also be monitored by assessing damageto volunteer oilseed rape plants.Pest damage can be monitored as soon as cropsemerge. The amount of leaf area eaten will determinethe need for treatment.Yellow water traps need to be examined regularly tomake counting as easy as possible. Set four yellowwater traps in early September: two on the headlandand two in the field along a wheeling. Fill them withwater and a drop of detergent. Record the number ofcabbage stem flea beetles in the traps weekly, ifpossible, before emptying and resetting. Remove thetraps at the end of October.Plant dissection involves taking a random sample of 25plants from the field in late October/early November.Samples are best dissected by an accredited laboratory.ThresholdsAssessing the need to spray adults in oilseed rape:– >25% leaf area eaten at the cotyledon–2 leaf stage– >50% leaf area eaten at the 3–4 leaf stage– The crop is growing more slowly than it is beingconsumedAssessing the need to spray larvae in oilseed rape:– >35% beetles/yellow water trap caught in total overthe monitoring period– >2 larvae/plant, when dissected– >50% of petioles damagedNon-chemical controlThe main natural enemy is the wasp Tersilochus microgaster, which parasitiseslarvae in the spring. All parasitoids may be vulnerable to pyrethroids. Parasitoidsremain as pupae in the soil until the next season, and may be damaged byploughing. Minimum cultivation after rape favours parasitoid survival. Other naturalenemies include spiders, ground beetles and rove beetles.Insecticide resistanceResistance to pyrethroids has been confirmed in the UK.© ADASAdult cabbage stemflea beetle damage onoilseed rape© Dewar Crop ProtectionCabbage stem fleabeetle damage tovolunteer oilseed rape© ADASCabbage stem fleabeetle larva21Pests: BeetlesPests: Beetles22

Cabbage stem weevil (Ceutorhynchus quadridens)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceCabbage stem weevil is frequently recorded in oilseedrape, occasionally causing economic damage.It can infest vegetable brassicas and may causecosmetic damage to high value crops, such ascauliflower. Damage can be caused by feeding adultsas well as larvae. It is currently an occasional andminor pest of vegetable brassicas.Risk factorsSpring crops in the southern counties are at particularrisk. It is considered a minor pest in winter crops.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 11 Adults overwinter in sheltered locations.23Adults migrate into the crop, laying eggs underthe leaf surface.Eggs hatch and larvae tunnel into the stem. Atmaturity, they bore an exit hole and pupate inthe soil.4 Adults emerge and feed for a short time.34© ADASCabbage stem weevilCabbage stem weevil (Ceutorhynchus quadridens)Identification and symptomsAdults are small (3 mm long) with a long snout,reddish legs and antennae. They have a fine layer ofyellow-white scales on the back that give them amealy appearance and a white spot in the middle ofthe back.Clusters of eggs are laid under the leaf surface in ablister. On hatching, larvae bore into the main stem tofeed. They are creamy white with a brown head andno legs and grow to 4–5 mm long. At maturity, theybore an exit hole in the lower stem and drop to thesoil to pupate.Plants invaded by this weevil show few external signs of damage. Blisters near themain vein on lower leaves and leaf stalks in early summer indicate where eggshave been laid. Larval feeding and tunnelling can result in premature leaf drop anddiscolouration to the stem. Some stunting and loss of vigour can occur, especiallyin spring rape. In late summer, exit holes in the stem should be visible.MonitoringCrops can be checked in early summer for adults migrating in from overwinteringsites. It is possible to trap adults in yellow water traps which may indicate whenfemales are laying eggs. These numbers are reported in the HDC Pest Blog.ThresholdsNone established.Non-chemical controlEarly drilling can minimise the risk of damage, as established plants will show agreater tolerance to the feeding.Natural enemies include spiders, ground beetles, rove beetles, predatory flies, andparasitoids of egg, larval and adult stages.Insecticide resistanceNone known.© University of WarwickDamage by cabbagestem weevil23Pests: BeetlesPests: Beetles24

Pea and bean weevil (Sitona lineatus)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrots25Alliums✔ Peas✔ Field beansSugar beet© PGROLettucePea and bean weevilLife cycleImportanceThe pea and bean weevil can cause yield reductions infield and broad beans and in combining, vining andfresh market peas. Adult feeding does not normallycause significant damage but larval feeding within theroot nodules can affect yield. The larvae are difficult totarget and pressure from this pest has increased inrecent years.Adults can transmit the broad bean stain virus (BBSV)and the broad bean true mosaic virus (BBTMV), whichcan affect product quality and result in large yieldreductions if the infection occurs early.Risk factorsCrops are at increased risk if leguminous plants, suchas clover and lucerne, neighbour the field or there areuncultivated grasses at field edges, especially if thefield or fields nearby were previously cropped withpeas or beans.Migration occurs in early spring and often when themaximum air temperature exceeds 15°C. Any cropsthat are newly emerged at this point are particularlysusceptible to damage from adult feeding.Crops grown in nitrogen-poor soil or exposed todrought conditions are most susceptible to larvalfeeding damage.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 3 1Pests: Beetles2 541 Adults emerge and overwinter in grasses and leguminous crops, such asclover and lucerne.2 Adults migrate into crops when temperatures rise above 15°C for short periods.3 Eggs are laid and are washed into soil at the crop base.4 Eggs hatch and larvae enter root nodules to feed.5 Larvae pupate in soil.Pea and bean weevil (Sitona lineatus)Identification and symptomsAdults are 4–5 mm long and light brown with faintcreamy yellow stripes along the length of the wingcases. They have a short ‘snout’ with the ‘elbowed’antennae typical of weevils.Eggs are oval and white when laid but darken as theymature. They are laid on or around crops and arewashed into the soil around the stem bases.Hatching larvae are legless and white with a brownhead. When fully grown, they are 4–5 mm long andmove out of the root nodules to form a pupa about5 cm below the soil surface.Adult feeding damage is evident as notching around the leaf margins and is usuallyfirst noticeable at field edges. Larval damage is difficult to detect. BBSV and BBTMVcause leaf malformation with light and dark green mottling and yellowish blotching.MonitoringA monitoring system that detects adult weevils migrating into the crop in early springhas been developed by Rothamsted Research, in collaboration with PGRO and ADAS.The system comprises five cone traps containing pheromone lures, which are sitedon a single grassy verge or headland of a field that had contained peas or beans theprevious year. The traps should be placed by mid-February and monitored threetimes a week until a threshold catch is reached or until the latest sown crops haveemerged (whichever is the sooner).The system identifies when weevil numbers are low and crops do not requiretreatment, identifies periods of peak activity to allow optimal timing of treatmentsand informs the selection of drilling time to avoid periods of serious damage.ThresholdsSpring-sown peas and spring field beans: An average of 30 or more weevils onany one recording day.The crop may be at risk if the threshold is reached when the crop has just emergedor is due to emerge in the next ten days.Non-chemical controlAvoid cropping in areas that have previously had large pea and bean weevilpopulations. Natural enemies include spiders, ground beetles, rove beetles,predatory flies and parasitoids.Insecticide resistanceResistance to pyrethroids is suspected.© PGROPea and bean weevildamagePests: Beetles26

Pollen beetle (Meligethes spp.)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceIn oilseed rape, adult and larval feeding can lead tobud abortion and reduced pod set. This damage rarelyresults in reduced yields for winter crops but springcrops can be more vulnerable as the susceptible green/yellow bud stage often coincides with beetle migration.Adults are occasional pests of cauliflower andbroccoli, feeding on the curds or florets in midsummerwhen new adults emerge from oilseed rapecrops and move into other areas to feed.Risk factorsCrops are usually most at risk when the weather isdry and warm (above 15°C).The damage-susceptible stage of the oilseed rape crop is green to yellow bud.Oilseed rape will usually compensate for early damage by producing more andlarger seeds on lower racemes. Backward crops and those suffering from pigeondamage are at greater risk.In vegetable brassicas, the risk of infestation is higher if horticultural crops are closeto fields of oilseed rape.© Dewar Crop Protection© Emily GrahamPollen beetle (Meligethes spp.)Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 134 51 Adults overwinter in sheltered spots.2 Adults migrate into oilseed rape crops whentemperatures exceed 15°C. They feed on polleninside buds or in open flowers.3 Eggs are laid in buds.4 Larvae feed on pollen before pupating.5 Adults emerge and feed on a variety of plants.Once the crop starts flowering, the beetles move tothe open flowers, becoming pollinators rather thanpests.Identification and symptomsThe adults are small (approx. 2.5 mm), metallicgreenish-black and have clubbed antennae.Females bite slits in the base of oilseed rape buds andlay their eggs inside.The larvae are creamy white, with a black head, threepairs of legs and dark brown spots and short bristlesalong the back. They grow to 3–4 mm long.Adults and larvae attack buds and flowers, resulting inwithered buds and reduced pod set.© Dewar Crop ProtectionPollen beetles on oilseed rapePollen beetles on oilseed rapeBlind stalks on oilseedrape due to pollenbeetle damage27Pests: BeetlesPests: Beetles28

Pollen beetle (Meligethes spp.)Pollen beetle (Meligethes spp.)© Dewar Crop ProtectionMonitoringOilseed rapeEstimate plant population per m 2 by counting thenumber of plants within a square foot and multiplyingby 11. This is easiest at the 5–6 leaf stage. Ideally,make a number of estimates of plant population andcalculate the average. Use the plant population todetermine the threshold.Count adults on the plant during the green bud stage.Once the crop is in flower, it is no longer at risk.Non-chemical controlPollen beetle larvae are attacked by parasitic wasps.They are relatively poor dispersers, so planting oilseedrape crops close to where the crop was grown in theprevious year can help ensure parasitism.The parasitic wasps may not be affected byinsecticides applied against pollen beetle at greenbud, as they arrive in crops during flowering. Whereinsecticides are used extensively, however, levels ofparasitism can be considerably decreased.© Dewar Crop ProtectionPollen beetles damagingoilseed rape bud© Jon OakleyVegetable brassicasThe HDC pollen beetle forecast (currently available onthe HDC Pest Bulletin website) predicts when adultpollen beetles will emerge from oilseed rape cropsand migrate into vegetable brassica crops and otherlocations, helping growers to target crop walking.ThresholdsOilseed rapeThe threshold scheme is based on the maximumnumber of buds each beetle can destroy and thenumber of excess flowers produced by differentcrops. Plant population is important, as low plantpopulations tend to produce more branches andmore flowers.– If there are fewer than 30 plants/m, 2 the thresholdis 25 pollen beetles per plant– If there are 30–50 plants/m, 2 the threshold is18 pollen beetles per plant– If there are 50–70 plants/m, 2 the threshold is11 pollen beetles per plantMinimum tillage following oilseed rape will enhancesurvival of the parasitic wasps. Trap cropping withturnip rape can attract more parasitoids into the cropand can often reduce populations of pollen beetle tobelow spray thresholds.Natural enemies also include spiders, ground beetlesand rove beetles.Insecticide resistancePollen beetle resistance to pyrethroid insecticides isnow widespread throughout the UK. A strategy forcontending with pyrethroid resistance needs to coverall spring and early summer insecticide applications,regardless of their intended target.Investigate any control failures to further establishresistance levels. Consider neonicotinoids, indoxacarbor pymetrozine as alternatives to pyrethroids.To limit the spread of resistance and any impacts onnon-target pollinators, pyrethroid sprays should onlybe used when thresholds have been exceeded andduring the green to yellow bud stage.Pollen beetle damageto spring rape© University of Warwick– If there are more than 70 plants/m, 2 the thresholdis 7 pollen beetles per plantVegetable brassicasNone established.Pollen beetle onoilseed rape budPollen beetle damageto cauliflower29Pests: BeetlesPests: Beetles30

Rape winter stem weevil (Ceutorhynchus pictarsis)Rape winter stem weevil (Ceutorhynchus pictarsis)Crops affectedCereals✔ OilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceRape winter stem weevil is an occasional pest ofoilseed rape. It first came to attention in 1982, when anumber of severe infestations were experienced inthe east and south east. The main damage is causedby the larvae feeding within stems; adult feeding inthe autumn is not considered important.Risk factorsInitially limited to Lincolnshire and Cambridgeshire,the pest has now spread to other areas. Attacks areoften worse near wooded areas.Identification and symptomsAdults are 2.5–4 mm long, metallic black beetles, withelongated snouts, branched antennae and reddishbrownleg tips.Eggs are laid in leaf petioles and other crevices on theplant.Hatching larvae are white, plump and legless, with anorange-brown head end. After hatching, they burrowinto the leaf petiole and from there into the stem anddown to the crown of the plant, where numerouslarvae can congregate in clusters. At maturity, theycan reach 5 mm in length, at which point they leavethe plant and drop to the soil to pupate.© ADASAdult rape winter stemweevilLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12334Adults emerge from the soil and disperse towoods and hedges, where they enter a restingphase.Adults invade autumn-sown oilseed rape crops,feeding on leaves.1 2Eggs are laid in punctures and crevices in the leafstalk and plant crown. Hatching larvae bore intothe stem to feed.4 Fully fed larvae descend to the soil to pupate.© ADAS3Adult rape winter stemweevilThe impact of larval feeding can vary widely,depending on the number of eggs laid on the plant.The larvae can destroy the terminal shoot, with theresult that some plants may die during the winterwhile others survive by developing secondary shoots,producing a stunted plant with a rosette-likeappearance. Attacked crops tend to be irregular andpatchy with uneven flowering and ripening.MonitoringAs adults are difficult to spot and larvae arechallenging to find, monitoring this pest can bedifficult. Where crops have previously been attacked, itis worthwhile inspecting the crop for young larvaefrom late October.ThresholdsNone established.Non-chemical controlNatural enemies include spiders, ground beetles, rovebeetles and several parasitoid species.Insecticide resistanceNone known.© Dewar Crop ProtectionRape winter stemweevil larva© SyngentaRape winter stemweevil damage31Pests: BeetlesPests: Beetles32

Wireworms (Agriotes spp.)Wireworms (Agriotes spp.)Crops affected✔ CerealsOilseedsVegetable brassicas✔ Potatoes✔ Carrots✔ Alliums✔ Peas✔ Field beans✔ Sugar beet✔ Lettuce© Dewar Crop ProtectionWireworm© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightWirewormsImportanceWireworms are the soil-inhabiting larvae of clickbeetles (Elateridae). They are typically found ingrassland but can attack a wide range of crops.Wireworm feeding on potatoes can cause significantreductions in tuber marketability, even at lowpopulations. This can make the difference between acrop worth >£100/tonne and one ploughed in at asignificant loss.In cereals, wireworms can affect all winter cereal orwinter cereal/grass ley rotations and have become aserious pest since the withdrawal of organochlorineinsecticides. Heavy infestations can cause yield lossesof up to 0.6 t/ha.Young sugar beet seedlings are susceptible towireworms. Injury shows as small wounds that soonblacken on the stem below soil level. The wound issmall but is usually enough to make the seedling wiltand die.Leeks are also prone to damage and heavyinfestations can cause entire crops to be lost.The larvae burrow into the roots of crops, such ascarrot, and damage vegetable seedlings.Risk factorsA pre-planting assessment of the risk of wireworminfestation is essential to developing a managementstrategy, as available chemicals can only be used atplanting.Crops sown within two years of ploughing outpermanent pasture are at highest risk; however, anyrotation with predominant winter cropping, particularlywith grass weeds, is at risk.An increased risk has also been associated withsouth-facing sloping fields, heavy alluvial soils andminimum tillage cereal crops. Late-lifted potatoes arealso at greater risk of wireworm damage.Life cycleAdult click beetles live for about a year. Larvae feed for five years before pupating.Numbers increase over the years; largest populations occur in old permanentpastures. Wireworms feed in ploughed-down turf for about six months beforemoving to the surface to damage the next two crops.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3 11 Adults overwinter below soil surface.2 Females lay eggs just below the soilsurface.3 Eggs hatch.4Identification and symptomsThere are three key species: Agriotes lineatus,A. obscurus and A. sputator. The larvae of the threespecies are indistinguishable by conventional means.Newly hatched wireworms are transparent, white and1.3 mm long. They grow to up to 25 mm long and ashiny golden brown. They have a cylindrical body,tough skin, three pairs of legs at the head end andtwo dark spots at the tail. The head is dark brown,with powerful biting mouthparts. They develop veryslowly, taking four to five years to reach maturity.Adults (click beetles) have a dark brown to blackelongated body (8–15 mm long and 2–3 mm wide),which is covered in fine whitish-grey hairs. The adultslive for about a year.Larvae leave ragged holes at the base of the stem incereals, sugar beet and leeks, moving along rows toattack further shoots. Damage to potato tubers andcarrots is visible as small, round holes on the surfaceleading to narrow tunnels.544 Larvae (wireworms) feed.5 Larvae pupate.© Dr Robert McBride, Gore New ZealandWireworm in potatoes© ADASWireworms and clickbeetle33Pests: BeetlesPests: Beetles34

Wireworms (Agriotes spp.)Wireworms (Agriotes spp.)© ADASClick beetlepheromone trap© Bayer CropScienceAdult click beetle© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightMonitoringBait and pheromone traps can be used to determinethe presence or absence of wireworms and clickbeetles, respectively. There is no clear relationshipbetween wireworm infestations and the numbers ofclick beetles caught in pheromone traps orwireworms caught in bait traps, they just indicatepresence or absence.Soil samples can be used to assess population sizeand provide a reasonably good estimation ofsubsequent damage in potato crops. Populations canbe very patchy, however, so accurate estimations aredifficult and wireworm populations are capable ofcausing significant damage even at the lower limit ofdetection in potato crops (60,000 per hectare).For cereals, examining soil cores in the field for largerwireworms or in the laboratory for smaller ones iscostly and rarely justified.ThresholdsPotatoes: The presence of even a single wireworm intwenty 10 cm diameter soil cores (equivalent toapproximately 60,000 per hectare) can represent asignificant risk in the following crop.Cereals: If wireworms exceed the threshold of750,000 per hectare (as determined by soilextraction), use a seed treatment. Even where a seedtreatment is used, damage can still occur under highpest pressure (1.25 million per hectare).Non-chemical controlConsolidating seedbeds helps restrict movement ofthe pest and controlling grass weeds can reduceavailability of food sources. Rolling a thin crop mayalso encourage tillering. In arable rotations, ploughbasedcultivation may help to reduce populations. Aspring rotation in cereal crops can also be beneficial.For potatoes, avoid wireworm-infested fields entirelyand consider lifting the crop early if damage isexpected.The main natural enemies are fungi and parasiticwasps. Larval stages are attacked by ground beetlesand adults are eaten by birds.No commercial biological control agents are currentlyavailable for controlling wireworms, although somestrains of the insect-pathogenic fungus Metarhiziumanisopliae have shown encouraging results underexperimental conditions.The use of cruciferous plants as green cover crops orde-fatted mustard meals as soil amendments hasbeen shown to reduce wireworm populations in Italybut the results have not yet been reproduced in theUK.Insecticide resistanceNone known.© Rothamsted Research Ltd© Rothamsted Research LtdWireworm and damageto sugar beet seedling© Rothamsted Research LtdWireworm damagein sugar beetOther crops: None established.© Image courtesy of The Food and Environment Research Agency (Fera), Crown CopyrightWireworm damage inonionWireworm damage in onionWireworm damage in sugar beet (left: treated; right: untreated)35Pests: BeetlesPests: Beetles36

Minor and/or emerging pestsCereal ground beetle (Zabrus tenebrioides)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceCrops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceThe cereal ground beetleattacks crops in England,from Oxfordshire andCambridgeshire southwards.Larvae burrow into soil,pulling down and eatingshoots from October toMay. Adult beetles feed oncereal ears before harvestand on split grain andstubble re-growths.Cereal leaf beetle (Oulema melanopa)© Jon OakleyCereal ground beetleDamage is worst in all-cereal rotations and withminimal cultivations. A non-cereal break crop or earlyploughing will provide good control.The cereal leaf beetle iscommonly seen in cerealcrops, especially oats,across the country frommid-summer.Adults and larvae eat longthin strips from the leaves,occasionally leaving thelower epidermis intact.© ADASCereal leaf beetle larvaThey are very rarely of economic importance andpredation usually keeps the population in check.The larva has the unedifying habit of covering itselfwith its own excrement, and can easily attach itself toyour trousers when walking through the crop.Minor and/or emerging pestsChafer grubs (Melolontha melolontha)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuceThe most commonspecies of chafer in the UKis the cockchafer or Maybug. Adult beetles arelarge (2.5 cm long) with areddish-brown body andblack head. They fly in Mayto feed in woodlands andlay eggs in the soil ingrassland or cereals duringthe summer. Larvaedevelop over the nextthree years and are mostdamaging in their secondor third year. Attacks arelocalised and sporadic andcontrol is not usuallyeconomically justified.Colorado beetle (Leptinotarsa decemlineata)Crops affectedCerealsOilseedsVegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightChafer grub© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightAdult chafer beetleThe Colorado beetle is a serious pest of potatoes;however, it is not established in the UK and is anotifiable quarantine pest. It originated in NorthAmerica but in 1922 it gained a foothold in France andhas since spread to most European countries.A single fertilised beetle canestablish a breedingcolony, so contact yourlocal Defra Plant Healthand Seeds Inspector if youfind or suspect thepresence of the beetle in acrop or importconsignment.© David KerfootColorado beetle37Pests: BeetlesPests: Beetles38

Minor and/or emerging pestsMinor and/or emerging pestsOther flea beetlesCrops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuce© Frank PorchTurnip flea beetle© Rothamsted Research LtdFlea beetle damage tosugar beetA number of flea beetles, including Wessex, stripedand turnip flea beetles, cause occasional cropdamage. Phyllotreta species can be very damagingpests of seedling crucifers, for example, swede androcket.The Wessex flea beetle is of increasing importance insouthern England and is most likely to damage earliersownoilseed rape crops, especially if they are slow togrow away in September. Crops can be severelychecked.The striped and turnip flea beetles are principally pestsof spring brassicas, of which later-sown crops aremost susceptible; however, any crop may be at risk ifgrowth is checked by sunny, dry weather.Adult beet or mangold flea beetles can cause seriousdamage to the upper or lower surface of cotyledons,leaves and petioles of sugar beet. They overwinter insheltered spots (field margins or hedges) and emergein spring. Eggs are laid in late spring and larvae feedon roots before pupating but the damage is caused byadult feeding in the spring. They are most damagingwhen they are present in large numbers, in cold, dry,sunny weather, and when soil temperatures are lowand plant growth is slow.Linseed is also particularly susceptible to flea beetles.All of these beetles are smaller than the cabbagestem flea beetle (page 21).Pygmy beetle (Atomaria linearis)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuce© Rothamsted Research LtdPygmy beetleCrops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceA small, elongate beetle of 2 mm in length, the pygmybeetle can damage sugar beet seedlings. Damage afterthe six true leaf stage is rarely of economic significance.Beetle bites on the root and hypocotyl cause small blackpits, which may allow invasion by parasitic fungi. Severedamage can destroy the vascular tissue, causing theseedling to collapse. Cotyledons and leaves may also beeaten, leaving irregular-shaped holes.The adults overwinter in the soil and survive on beetcrowns left after harvest. In spring, they move to the soilsurface and fly on warm, still days from May onwards tocolonise new beet fields. In dry weather, the beetlesmove deep into the soil. In humid weather, they move tothe soil surface and feed on the hypocotyl and leaves.Eggs are laid in late spring and summer and the larvaefeed on roots of well grown plants, causing little damage.Seedlings are most sensitive to damage from adults infields where beet is grown in close rotation or wherecrops are infested early from adjacent fields with beetthe previous year. Rotation is usually the most effectivecontrol.Wheat shoot beetle (Helophorus nubilus)The wheat shoot beetleis an occasional pest ofwinter cereals following agrass rotation.The larvae feed at thebase of the shoot,causing the plant orcentral leaves to yellowand die.© Dr Christoph Benisch – kerbtier.deDamage is usually seen Wheat shoot beetlefrom January to Marchbut can be avoided by leaving a sufficient intervalbetween ploughing grass and drilling the crop – amonth should be sufficient under most conditions.39Pests: BeetlesPests: Beetles40

Further informationAlerts and bulletinsHDC Pest Bulletin: Sponsored by Syngenta and hosted on the Syngenta website,this bulletin aims to provide growers with topical and valuable agronomyinformation throughout the growing season.www3.syngenta.com/country/uk/en/AgronomyTools/HDCPestBulletinHDC PublicationsAvailable at www.hdc.org.ukHDC Factsheet 35/12: Minor pests of Brassicas (2012)HDC Factsheet 25/11: Control of bruchid beetle on broad beans (2011)HDC Factsheet 22/10: Control of flea beetles and other key insect pests of leafysalad Brassica crops (2010)HGCA PublicationsAvailable at www.hgca.com/publicationsHGCA Information Sheet 24: Cabbage stem flea beetle (2014)HGCA Information Sheet 18: Monitoring and control of pollen beetle in oilseedrape (2013)HGCA Research Review 77: Implications of the restriction on the neonicotinoids:imidacloprid, clothianidin and thiamethoxam on crop protection in oilseeds andcereals in the UK (2013)Potato Council PublicationsAvailable at www.potato.org.uk/knowledge-hubGrowers' advice – Wireworm factsheet (2011)Information from other organisationsFera Plant Pest Factsheet: Potato flea beetles (2011)Fera Plant Pest Factsheet: Colorado beetle: Identification (2011)Fera Plant Pest Factsheet: Colorado beetle (2006)41Pests: Beetles

Pests:Bugs and aphids

Contents – Pests: Bugs and aphidsSpeciesPageBird cherry–oat aphid (Rhopalosiphum padi) 43Black bean aphid (Aphis fabae) 45Buckthorn–potato aphid (Aphis nasturtii) 47Cabbage whitefly (Aleyrodes proletella) 49Currant–lettuce aphid (Nasonovia ribisnigri ) 51Grain aphid (Sitobion avenae) 53Lettuce root aphid (Pemphigus bursarius) 57Mealy cabbage aphid/Cabbage aphid (Brevicoryne brassicae) 59Pea aphid (Acyrthosiphon pisum) 61Peach–potato aphid (Myzus persicae) 65Potato aphid (Macrosiphum euphorbiae) 69Rose–grain aphid (Metopolophium dirhodum) 71Tarnished plant bug (Lygus rugulipennis) 73Willow–carrot aphid (Cavariella aegopodii ) 75Minor and/or emerging pests 77Potato leafhoppers 77Further information 79

Bugs (Hemiptera)Bugs (Hemiptera) include true bugs (Heteroptera), aphids and white flies(Sternorrhyncha) and hoppers (Auchenorrhyncha). Many species are plant-feedingpests but there are also some natural enemy species (see page 181).Life cycleBugs can have complicated life cycles and aphids are the best example of this. Thelife cycles of other bugs (for example, whiteflies and hoppers) retain the same basicfeatures but are often simpler.Most agronomically important aphid species have separate winter and summerhosts. In spring, when conditions are suitable, new individuals emerge and developinto fundatrices (a). These reproduce asexually and their offspring develop wingsbefore migrating to summer hosts (b). Many more asexual generations areproduced on thebsummer hosts (c).Winter hostSummer hostIn the autumn,awinged males andfemales areproduced, whichSpring migrantOverwintering stagemigrate back to thewinter host (d). Thesethen mate andoverwinter, either aseggs (e) or activestages. Some aphidspecies are able toreproduce asexually all year.edAutumn migrantscSummerreproductionDefining featuresBugs are characterised by theirsucking mouthparts, comprising of apiercing, segmented rostrum andcompact, often flattened bodies. Thefront pair of wings is usually leatheryand the back pair is usuallymembranous.HeadAntennaeSiphunculus(emits alarm pheromones)Cauda (tail)ThoraxAbdomenImmature aphid and plant bug stages(nymphs) resemble smaller versionsof the wingless adults, while whiteflynymphs resemble oval, flattenedscales. Nymphs progress through anumber of 'instar' stages before becoming adults.Rostrum(used for feeding)LegsPests: Bugs and aphids42

Bird cherry–oat aphid (Rhopalosiphum padi)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceThe bird cherry–oat aphid is an important vector ofbarley yellow dwarf virus (BYDV), particularly in thesouth west of England. Even very small populations,which may go unnoticed, can cause economicdamage by transmitting BYDV.Rarely, direct feeding by this pest can also damagecereal crops. It can also infest sweetcorn.Risk factorsWinter crops: Crops sown early, particularly in a warmautumn, are most susceptible to bird cherry–oat aphidattack. These conditions allow aphids to breed rapidly.However, a crop should suffer little yield loss fromnew BYDV infection after GS31.Spring crops: After mild winters, BYDV may be transmitted to late-sown crops bywinged aphids.All crops: BYDV is most damaging to plants infected in the early growth stages.The effects of BYDV may be exacerbated by other stress factors, including adverseweather conditions, soil acidity and other pests and diseases.Life cycle1Eggs overwinter on bird cherry trees (Prunuspadus).2 Eggs hatch.3 Winged forms migrate to cereals and grasses.45Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3 4 51Multiple generations occur, infesting lower leavesand stems first.Winged forms migrate back to bird cherry trees.In mild conditions, asexual forms can remain andfeed in cereal crops.© ADASBird cherry–oat aphidBird cherry–oat aphid (Rhopalosiphum padi)Identification and symptomsThe adult aphids are 1–2 mm long, broadly ovalshapedand green to dusky brown, with rust redpatches at the rear. Winged adults are a similar sizewith a pale to dark green abdomen.The initial symptoms of BYDV infection are normallyseen as individual plants scattered through the cropwith bright yellow upper leaves. Later, as infectionspreads, larger areas of the crop become infected,appearing as patches of bright yellow and severelystunted plants.MonitoringSerious losses due to BYDV can be caused by verysmall numbers of bird cherry –oat aphids. AHDB AphidNews provides information on aphid migration and anindication of risk to crops.ThresholdsNo satisfactory thresholds for treatment exist. Ifaphids are present, it should be assumed that theyare carrying BYDV.Non-chemical controlGround beetles, spiders and parasitoids are natural enemies that are active inautumn and winter, although the latter may only be so in mild winter weather.Minimum tillage, grass banks and field margins provide habitats for these naturalenemies but can also harbour infective aphids. Beetle banks should be consideredin large arable fields of 20 ha or more.If high levels of aphid-infested grasses, especially annual meadow grass, arepresent in the stubble, a desiccant herbicide or ploughing may be beneficial toremove this green bridge. However, the risk of infestation by winged aphids in theautumn is lower following minimum tillage, and more so if the straw is left,compared to ploughing. Delaying sowing so that crops emerge after the end of theaphid migration (usually early November) will also reduce BYDV risk but this is notalways practical.If a spring barley crop follows a mild winter or is in a milder area, it may beworthwhile choosing a moderately resistant variety (see HGCA RecommendedList).Insecticide resistanceNone known.© Dewar Crop ProtectionBird cherry–oat aphid© Dewar Crop ProtectionBarley yellow dwarfvirus symptoms43Pests: Bugs and aphidsPests: Bugs and aphids44

Black bean aphid (Aphis fabae)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeas✔ Field beans✔ Sugar beetLettuceImportanceThe black bean aphid can cause significant damage tofaba bean crops. Damage mainly occurs through thedirect feeding of the pest, which can result in yieldreductions if aphid populations grow large enough.These aphids also transmit viruses, such as bean leafroll virus (BLRV), pea enation mosaic virus (PEMV),bean yellow mosaic virus (BYMV) and beet yellowsvirus (BYV).The production of honeydew during feedingencourages chocolate spot (caused by Botrytis spp.),which can reduce the yield of the crop.On spinach and sugar beet, populations can developrapidly on the undersides of leaves, which as a resultbecome chlorotic and crinkled.Risk factorsLate-sown spring crops are most at risk, as plants may be less well established andyet to flower.Control of early invading aphids is essential to prevent virus infection. Colonies cangrow rapidly in the summer, especially if conditions are warm and humid.There is a tendency for serious infestations to occur in alternate years, so severeattacks can be expected in a year following little or no infestation.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 12 431234Eggs overwinter on spindle (Euonymus europaeus).In mild winters, active stages may overwinter onleguminous weeds or winter beans.Winged forms appear and migrate into a widerange of summer crops.Breeding continues throughout the summer,usually peaking in July/August. Further wingedforms are produced in response to crowding,spreading within the crop and to other crops.Winged forms migrate back to spindle to lay eggs.© ADASBlack bean aphidsBlack bean aphid (Aphis fabae)Identification and symptomsThe wingless adults are 1.5–3 mm long, black or olive green and often havedistinct waxy stripes on the upper surface of the abdomen. Winged adults are verydark with faint black crossbars on the upper surface of the abdomen. Colonies areoften noticeably attended by ants. A colony can become very large and dense,numbering in the hundreds, and develops from the top of the plant downwardsonto the leaves and developing pods as it grows.Direct feeding can damage flowers, retard or even prevent pod development andcause plants to lose vigour and wilt in dry conditions.BLRV causes leaf yellowing, upward leaf-rolling and a decrease in pod numbers.Symptoms are often more obvious if the aphid invades the crop before flowering.PEMV in beans causes vein clearing and the formation of translucent spots, whichare apparent when infected leaves are held up to the light. Upper leaves becomepointed and crinkled and may contain necrotic spots. Symptoms of an advancedinfection are the cessation of terminal growth, the disappearance of axillary budsand impairment of flower set.Following BYMV infections, leaves become crinkled and occasionally pointed, theplant becomes stunted and vein clearing may occur. Symptoms can be mistakenfor PEMV but without the translucent spotting and streaking on the leaf surface.Direct feeding damage on sugar beet can occur but is rarely worth controlling.MonitoringInspect the crop regularly from early flowering until pod formation. Colonies tend toappear on the headlands first. This aphid is included in the HDC Pest Bulletin.ThresholdsIn beans, immediate treatment is justified when 10% of plants are infested.Treating the crop when 5% of plants are infested can help prevent virus infection.In sugar beet, treatment is only justified on backward or stressed crops with morethan 100 aphids per plant (averaged across the field and not just on headlands).Non-chemical controlNatural enemies include parasitic wasps, ladybirds, hoverflies, lacewings andinsect-pathogenic fungi. Providing habitats that encourage the presence of thesemay help control aphid numbers. They may not be effective in preventing virustransmission, as this can occur even at low aphid densities.Insecticide resistanceNone known.45Pests: Bugs and aphidsPests: Bugs and aphids46

Buckthorn–potato aphid (Aphis nasturtii)Buckthorn–potato aphid (Aphis nasturtii)Crops affectedCerealsOilseedsVegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceBuckthorn–potato aphid is a relatively minor pest ofpotato. Populations rarely grow large enough to causeeconomic damage through direct feeding.This aphid can, however, transmit non-persistentviruses, such as potato virus Y (PVY) and potato virusA (PVA). It is thought to be a poor vector of thepersistent virus, potato leaf roll virus (PLRV).Risk factorsControl measures are usually unwarranted butpopulations can vary widely from year to year andwarm conditions in late spring/early summer canpromote large populations of the pest. Most directdamage is caused during tuber bulking in late July andAugust.Identification and symptomsThe wingless adult is relatively small (1–2 mm) andbright yellow-green.Very heavy infestations can seriously damage thehaulm and reduce yields.PVY infections caused by aphids result in leaf dropstreak, where lower leaves develop black streaks ontheir underside veins and eventually collapse, hangingoff the stem by a thread. Younger leaves may developnecrotic spotting.PVA infections usually cause mild mosaic symptoms.MonitoringBuckthorn–potato aphids are rarely caught in suctiontraps, so winged migration data is not available.© Bayer CropScienceBuckthorn–potatoaphids© The James Hutton InstituteLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec11231 Eggs overwinter on buckthorn.2Winged adults move into crops in May/June andreproduce throughout the summer.3 Winged adults migrate to buckthorn to lay eggs.© Bayer CropScienceThresholdsNone established. Control measures are usuallyunwarranted.Non-chemical controlNatural enemies include parasitic wasps, ladybirds,hoverflies, lacewings and insect-pathogenic fungi.Providing habitats that encourage the presence ofthese may help control aphid numbers. They may notbe effective in preventing virus transmission, as thiscan occur even at low aphid densities.Using seed potato certified by the British Seed PotatoClassification Scheme reduces the virus risk and itssubsequent spread by aphids. Potato varieties differ intheir susceptibility to aphid infestation and virusinfection. Seek expert advice on which variety tochoose if the crop is in a high-risk area.Insecticide resistanceNone known.Potato virus Y leafsymptoms© Bayer CropScienceBuckthorn–potatoaphidsBuckthorn–potatoaphid damage47Pests: Bugs and aphidsPests: Bugs and aphids48

Cabbage whitefly (Aleyrodes proletella)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceCabbage whitefly is a major problem because theimmature stages (scales) and waste products (mainlyhoneydew, which can lead to the development ofmould) contaminate plants and reduce quality. Thepresence of adults and scales can causecontamination issues in produce that is packed.Risk factorsThe cabbage whitefly has become an increasingproblem in recent years. The reason for this isunknown but it is believed to be due to a combinationof climate change, removal of certain activeingredients from use, insecticide resistance and laterharvest times of crops. Kale and Brussels sproutappear to be ‘preferred’ hosts and suffer the mostdamage in terms of a reduction in plant quality.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec121 Whiteflies overwinter mainly as adult females in© University of Warwicksheltered locations.2 Adults may migrate in substantial numbers whentemperatures are above 8°C. As temperatures rise,females will begin to lay eggs on leaves.3 For a short time after the egg hatches, the larva haslimited mobility but cannot leave the leaf on whichthe egg was laid. Once the larva finds a suitablelocation for feeding, it spends the rest of itsdevelopment attached to the leaf. After three moults,the larva develops into a pupa from which a new Cabbage whitefliesadult will emerge.Cabbage whiteflies are capable of multiple generations per year in the UK (two tofive). The rate of development and the start of reproduction are determined byambient temperature, so climate and weather conditions will dictate the maximumnumber of generations and the size of the population.31Cabbage whitefly (Aleyrodes proletella)Identification and symptomsThe adults are small, white moth-like insects about 1.5 mm long with two pairs ofblack spots on the forewings. The eggs are pale, elongated cylinders less than 0.1mm, laid in full or partial circles. The larvae are flat oval semi-transparent scalesfrom 0.3–1 mm. The pupae are off-white to brown flattened scales, with eyesvisible in the later stages.All life stages are likely to be accompanied by circular deposits of pale wax, whichcan be used as a sign of adult presence, even when no insects are observed.MonitoringAdult whiteflies can be captured on blue or yellow sticky traps. However, withincropmonitoring is probably the most effective approach.ThresholdsNone established.Non-chemical controlNatural suppression by whitefly predators is unlikely to provide substantial controlin most crops. Specialist whitefly natural enemies include parasitoid wasps(Encarsia inaron, Encarsia tricolor, Euderomphale chelidonii), a ladybird (Clitostethusarcuatus) and a fly (Acletoxenus formosus). Generalist predators of aphids will alsofeed on whiteflies in the absence of their primary prey.There may be some potential for inundative releases of parasitoids to providecontrol in crops. The potential for using biopesticides (eg fungal pathogens) toreduce whitefly populations has yet to be explored.Crop covers have been shown to reduce whitefly infestations by up to 71% whenapplied season-long in trials on Brussels sprout in Germany (for organic production).Fine mesh netting (0.8 x 0.8 mm) reduced or delayed immigration, even withperiodic cover removal for weeding. When combined with better knowledge ofpest ecology and forecasting, there is potential to disrupt pest infestations throughtargeted short-term covering after planting out.Studies have provided evidence of host plant resistance to whitefly in somebrassicas; however, commercial kale and Brussels sprout varieties with specificresistance to cabbage whitefly are not available currently.Insecticide resistanceResistance to the pyrethroid, deltamethrin, was found in whitefly samples takenfrom crops in southern and central England in 2009–2011. Such resistance wasshown to impair control in field trials. Whiteflies globally have been shown to rapidlydevelop resistance to a range of insecticides and effective products should becarefully managed to prevent this.49Pests: Bugs and aphidsPests: Bugs and aphids50

Currant–lettuce aphid (Nasonovia ribisnigri ) Currant–lettuce aphid (Nasonovia ribisnigri )Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beet✔ LettuceImportanceThe currant–lettuce aphid is the most importantfoliage aphid on lettuce. Rapid development ofcolonies causes plants to become stunted and evensmall numbers can contaminate plants and affectmarketability. In some cases, large populations onyoung plants may prevent 'hearting'.This species does not usually transmit lettuce mosaicvirus.Risk factorsThese aphids prefer to feed in the centre of the plantand can be extremely difficult to control once thelettuce plant has hearted.Identification and symptomsAdult wingless currant–lettuce aphids are 1–3 mmlong, green to yellowish-green and sometimesreddish. They have a shiny abdomen with a darkgreen-black pattern on the upper surface. There aretwo long tubes (siphunculi) at the rear end, with palebases and dark tips. The tail is pale, finger-shaped andabout two-thirds the length of the siphunculi.The winged form has black siphunculi and antennae,and a clear black pattern on the abdomen.MonitoringA day-degree forecast for currant–lettuce aphid isavailable as part of the HDC Pest Bulletin.Image Courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightCurrant–lettuce aphidnymphLife cycle12345Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3 45 1The aphid usually overwinters as an egg oncurrant or gooseberry bushes.Eggs hatch in March/April and the nymphs infestthe tops of the young shoots.Colonies are formed on the developing leavesand, in May/June, winged aphids migrate tolettuce and wild hosts.Several generations are produced on the summerhosts.During October/November, winged aphidsmigrate back to the winter hosts, where eggs arelaid. In warm locations, the mobile stages cansurvive and slowly reproduce on wild hoststhroughout the winter.© University of WarwickCurrant–lettuce aphidson lettuceThresholdsNone established.Non-chemical controlThe mobile forms are attacked by a number of naturalenemies, including ladybirds, hoverflies andlacewings. Young aphids may be parasitised by certainspecies of wasp, whose larvae eventually kill theaphid, which forms a hard gold-coloured ‘shell’ knownas a ‘mummy’.To date, biological control with natural enemies hasnot been evaluated comprehensively in the UK butthe efficacy of several biopesticides is beingevaluated.A range of cultivars of lettuce with completeresistance to currant–lettuce aphid have been availablefor a number of years. However, in recent yearscertain populations of currant–lettuce aphid haveovercome this form of resistance.Insecticide resistanceResistance to pirimicarb and pyrethroid insecticideswas detected in certain UK field populations someyears ago; however, the resistance does not appear tohave had a major impact on levels of control in thefield.Image Courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightWingedcurrant–lettuce aphid© University of WarwickCurrant–lettuce aphidson lettuce51Pests: Bugs and aphidsPests: Bugs and aphids52

Grain aphid (Sitobion avenae)Grain aphid (Sitobion avenae)Crops affected✔ CerealsOilseedsVegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© Dewar Crop ProtectionGrain aphids© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightImportanceGrain aphid is important as the main vector of barleyyellow dwarf virus (BYDV) in the east, middle andnorth of the UK, with losses up to 2.5 t/ha. Even verysmall populations, which may go unnoticed, can causeeconomic damage by transmitting BYDV.Grain aphid is an efficient vector of potato virus Y.Migration during late June and early July poses thegreatest risk of a high incidence of viruses withincrops. They can occur in potato crops in extremelyhigh numbers in summer, when they migrate fromdesiccating cereal crops into potato fields in search offood.The aphid also causes direct injury through feeding.Risk factorsBYDV: Risk of BYDV spread is significantly greater inmild winters through exposure to winged aphidsmigrating later into the season. Migrations cancontinue into November and infect later-sown crops.After mild winters, spring crops may be vulnerable toBYDV transmitted by winged aphids.BYDV is most damaging to plants infected in the earlygrowth stages.Direct feeding damage (summer): All cereals are atrisk of direct feeding damage, although winter barleyis less affected due to its earlier senescence. Thisspecies may also infest sweetcorn. Drought-affectedcrops or those damaged by other pests and diseasessuffer greater impacts, due to lower reserves ofsoluble stem carbohydrates.Increased risk is also associated with dry, settledweather during early grain filling. Outbreaks tend tooccur after colder winters, which reduce naturalenemy populations more than populations of thesecold-hardy aphids.Life cycle12Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec124 34Adults can overwinter on crops and grasses, they do not have an alternatewoody winter host.Fresh migrations infest crops from April. During dry, settled weathernumbers can increase rapidly. Crop senescence, rainfall and natural enemiesall act to limit population growth.3 Direct feeding is a risk from April until August.4 BYDV is a risk from September until around March (pre-GS31).In autumn, most aphids probably come fromgrasses, especially perennial rye-grass. The virusmay also be vectored from other cereal crops andvolunteers.Identification and symptomsThe grain aphid is large, long-legged and yellowishgreen,green or reddish-brown to nearly black.BYDV: The initial symptoms of BYDV infection arenormally seen as individual plants scattered throughthe crop with bright yellow upper leaves. Later, asinfection spreads, larger areas of the crop becomeinfected appearing as patches of bright yellow andseverely stunted plants.Direct feeding damage (summer): Only very severeinfestations produce visible symptoms in crops.Infested leaves turn yellow and senesce prematurely.Indirect damage is caused by the secretion ofhoneydew during feeding, which provides a mediumfor sooty moulds and a sugar source for flies,including pest species.© ADASGrain aphids on ear© Dewar Crop Protection1Grain aphidBDYV symptoms53Pests: Bugs and aphidsPests: Bugs and aphids54

Grain aphid (Sitobion avenae)Grain aphid (Sitobion avenae)© Dewar Crop ProtectionGrain aphids© Dewar Crop ProtectionGrain aphidsMonitoringBYDV: AHDB Aphid News provides information onaphid migration and an indication of risk to crops fromBYDV and direct feeding.Direct feeding damage (summer): To monitor fordirect feeding damage, check for aphids on the leavesinitially at about the time the cereals are coming intoear. Individuals move up to the ears during grain fillingand feed from the phloem supply to the grain.ThresholdsBYDV: Serious losses due to BYDV can be caused byvery few grain aphidsDirect feeding damage (summer):Before GS61: Half of tillers infestedGS61 to two weeks before end of grain filling: Twothirdsof tillers infested from stem extension to flagleafemergence or if more than 66% of tillers areinfested and numbers are increasing for the periodfrom flowering to watery ripe.Non-chemical controlIf a spring barley crop follows a mild winter or is in amilder area, it may be worthwhile choosing amoderately resistant variety (see HGCARecommended List).Autumn/winter: Ground beetles, spiders and parasitoids are natural enemies thatare active in autumn and winter, although the latter may only be so in mild winterweather. Spiders, especially web-building money spiders, are likely to be the mosteffective because they capture immigrating aphids and prevent their spread, arepresent in high numbers in the autumn and their webs continue to catch aphidsafter being abandoned. These spiders need some structures between which to buildtheir webs and so can be more abundant on cloddy seeds beds or those with trashpresent. They are highly vulnerable to pyrethroid insecticides.Spring/summer: Early in the aphid population growthphase, the generalist predators (spiders and beetles)provide background control, helping to prevent aphidsfrom reaching economically damaging levels. Onceaphid numbers build up, aphid-specific predators, suchas hoverflies, ladybirds and lacewings, and parasiticwasps become more important.Overall levels of natural enemies can be encouragedusing minimum tillage that allows field-overwinteringspecies to survive and provides structure for spiders.Grass banks and field margins provide overwinteringhabitats, alternative foraging sites and refuges insummer. While grasses can harbour infective aphids,they also help maintain populations of parasitic wasps,facilitating faster colonisation in spring. Beetle banksshould be considered in large arable fields of 20 ha ormore. Flower-rich habitats provide essential nectarresources for hoverflies and parasitic wasps, while alsosupporting alternative insect prey for many othernatural enemies.Insecticide resistanceCases of knockdown resistance (kdr) to pyrethroidsmay impact on product performance, particularlywhen sprays are applied at reduced field rates. It isimportant that full recommended pyrethroid field ratesare used. If control remains poor, a pyrethroid-basedproduct should not be used again and growers shouldswitch to an insecticide with an alternative mode ofaction.© ADASGrain aphids© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightGrain aphidsIf high levels of aphid-infested grasses, especially annual meadow grass, arepresent in the stubble, a desiccant herbicide or ploughing may be beneficial toremove this green bridge. However, the risk of infestation by winged aphids in theautumn is lower following minimum tillage, and more so if the straw is left,compared to ploughing. Delaying sowing so that crops emerge after the end of theaphid migration (usually early November) will also reduce BYDV risk but this is notalways practical.55 Pests: Bugs and aphidsPests: Bugs and aphids56

Lettuce root aphid (Pemphigus bursarius)Lettuce root aphid (Pemphigus bursarius)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beet✔ LettuceImportanceInfestations of the lettuce root aphid can reduce yieldand marketability. Severe infestations can also lead tosignificant crop losses.Risk factorsSymptoms are more severe in dry seasons becausethe aphids damage roots and reduce water uptake.Identification and symptomsAdult winged lettuce root aphids are 2 mm long andhave a dark head bearing short antennae. The thorax isdark brown or black and the abdomen is brownishorangewith a slight powdering of wax.Adult wingless lettuce root aphids have a yellow headwith green-grey antennae that are much shorter thanthe body. The body is yellowish-white and oftencovered in large quantities of white-grey wax. Thereare no siphunculi.The presence of lettuce root aphids is not apparentuntil plants start to wilt. Large infestations causeplants to wilt, dry up and turn yellow.© University of WarwickLettuce root aphidsLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3541MonitoringA day-degree forecast for lettuce root aphid is availableas part of the HDC Pest Bulletin.ThresholdsNone established.Image Courtesy of The Food andEnvironment Research Agency (Fera),Crown Copyright12345The aphid overwinters as an egg on Lombardyand black poplar trees.Eggs hatch into nymphs, which feed ondeveloping petioles, which enlarge to form gallswithin which the nymphs live and mature toproduce a further generation of aphids.Winged aphids appear over a 4–5 week period inlate June/July and migrate to lettuce and wildhosts.They produce live young as soon as they arriveon the lettuce plants and the wingless progenymigrate to the roots, where numbers increasethrough the production of several winglessgenerations.Winged aphids are formed and fly to poplartrees.© University of WarwickLettuce root aphid gallon poplarNon-chemical controlThe effects of lettuce root aphid attacks are worsewhen plants are under water stress. Irrigation can bevery beneficial for crops showing signs of damage.It is recommended that Lombardy poplars should notbe planted as windbreaks close to areas of lettucecultivation.Natural enemies, including ladybirds and hoverflies,attack the aphids in galls on poplar and also aphidcolonies feeding on lettuce roots.No attempts have been made to release biological control agents or to controllettuce root aphids with biopesticides.Cultivars of lettuce with almost complete resistance to lettuce root aphid (Avoncrispand Avondefiance) were developed in the UK but the material has not been used todevelop more modern cultivars.Insecticide resistanceNone known.Lettuce root aphiddamage57Pests: Bugs and aphidsPests: Bugs and aphids58

Mealy cabbage aphid/Cabbage aphid (Brevicoryne brassicae)59Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycle12Pests: Bugs and aphidsImportanceThe mealy cabbage aphid is a serious pest ofvegetable brassicas, where infestation leads todistorted foliage and contamination of produce byaphids, wax, cast skins and honeydew. Severeinfestations reduce yield and may even kill youngplants. In vegetable brassicas, it is also an importantvector of several viruses, including turnip mosaic virus(TuMV) and cauliflower mosaic virus (CaMV).Mealy cabbage aphid is not usually a serious pest ofoilseed rape.Risk factorsMild winters can allow infestations on winter oilseedrape to increase to damaging levels. Spring oilseedrape can become severely infested after mild winters.Hot, dry summers can cause large populations todevelop.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1While this species can overwinter as eggs onbrassica crops and wild hosts, it is thought thatmost overwinter as active stages on brassicacrops and wild hosts.The production of winged forms allows thisspecies to move to new brassica crops,multiplying rapidly in hot, dry conditions.2© University of Warwick1Mealy cabbage aphidsMealy cabbage aphid/Cabbage aphid (Brevicoryne brassicae)Identification and symptomsWingless aphids are bluish-grey, up to 2.6 mm long,with short transverse dark bars on the upper side ofthe thorax and abdomen, which is often covered in athick layer of wax.The first symptoms in vegetable brassicas are smallbleached areas on the leaves. The leaves then turnyellowish and become crumpled. Young plants can bestunted and may die in unfavourable weather.Early infestations in oilseed rape are found underleaves but later infestations move to developingflowers and pods, where they can produce densecolonies. Autumn feeding often causes leafdistortions, twisting of the mid-rib and chloroticpatches. The crop usually recovers in the spring. Inspring oilseed rape, serious infestations can causepod distortions and yield loss.On all crops, TuMV and CaMV cause leaf mottling andvein clearing, stunting, and black mottling andstreaking on stems.MonitoringAHDB Aphid News and the HDC Pest Bulletin provideinformation on aphid migration.ThresholdsWinter oilseed rape: >13% of plants infested beforepetal fallSpring oilseed rape: >4% of plants infested before petal fallVegetable brassicas: None establishedNon-chemical controlNatural enemies include parasitic wasps (eg Diaeretiella rapae), ladybirds,hoverflies, lacewings, a range of predatory flies, spiders, and insect-pathogenicfungi. Providing habitats that encourage the presence of these may help controlaphid numbers. They may not be effective in preventing virus transmission, as thiscan occur even at low aphid densities.Biopesticides are being evaluated for control of this pest.Insecticide resistanceNone known.© Emily GrahamMealy cabbage aphidson oilseed rape© University of WarwickMealy cabbage aphidson vegetable brassicacropPests: Bugs and aphids60

Pea aphid (Acyrthosiphon pisum)Pea aphid (Acyrthosiphon pisum)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliums✔ Peas✔ Field beansSugar beet© PGROPea aphids© PGROLettuceImportancePea aphid is a major pest of peas and beans. Attacksby the pest can result in reduced yields by spoilingflowers, causing pod filling to fail and by generallyreducing plant efficiency.The pea aphid also transmits a number of viruses,including pea seed-borne mosaic virus (PSbMV), peaenation mosaic virus (PEMV) and bean leaf roll virus(BLRV). PSbMV affects quality in vining peas and themaintenance of disease-free seed stocks. PEMV cancause large yield reductions in severe cases.Additionally, the honeydew produced by the pest canprovide an ideal medium for the growth of saprophyticfungi. It is very sticky and may increase the cost ofcleaning vining machinery.Risk factorsCombining peas are particularly vulnerable to peaaphid damage up until the development of the fourthpod-bearing node but if infestation occurs after thispoint no appreciable reduction in yield will occur.The presence of overwintering crops, such as cloverand lucerne, in neighbouring fields can increase therisk of aphids migrating into the crop in May.The most likely manner for PSbMV to becomeestablished is after the use of infected seed. The virusis transmitted by aphids in early spring.Crops are most at risk from PEMV if it is transmittedbefore flowering occurs.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1234561 2 361Eggs overwinter on forage crops. Active stagesmay overwinter in mild years.Eggs hatch.Wingless generations reproduce onoverwintering plants.Winged forms migrate to pea and legume crops.Aphids feed and reproduce rapidly on peas andlegumes, with highest numbers usually seenbetween late June and early July.Winged forms migrate to overwintering sites.Eggs are only laid at the beginning of winter onforage crops, such as lucerne, trefoils and clover,where they remain until hatching in the spring.During the summer, pea aphids produce live youngasexually, allowing populations to grow rapidly.© Ian F G McLean45© PGROPea seed-borne mosaicvirus symptoms© PGROPea aphidsPea aphidsPea aphids on a bean61Pests: Bugs and aphidsPests: Bugs and aphids62

Pea aphid (Acyrthosiphon pisum)Pea aphid (Acyrthosiphon pisum)© PGROPea enation mosaicvirus (PEMV)symptoms© PGROBean leaf roll virus(BLRV) symptomsIdentification and symptomsThe pea aphid is green with a pear-shaped body, longantennae and long legs. The winged females are2.5–3 mm long and have deep red or black eyes andyellowish-green antennae, while wingless females aresimilar but with a smooth, shiny skin.PSbMV causes vein-clearing, narrowing anddownward rolling of leaflets and foreshortening of theapical internodes. Pods on the upper parts of theplants may become stunted and develop a glossygreen appearance. A white blistering may alsodevelop over the seed coats as the peas mature inthe pod, giving the peas a ‘tennis-ball’ marking.PEMV causes vein clearing and the formation oftranslucent spots, which are apparent when infectedleaves are held up to the light. Development ofstipules (the leaf-like structures at the base of leaves)is often retarded and they can remain narrow, whileleaflets become crinkled and may contain necroticspots.The tops of the plants often become yellow andmottled with distorted leaves and pods may beseverely malformed and fail to fill. At an advancedstage of infection, enations may appear. These aresmall, irregular, protruding ridges of plant tissue foundon pods and the underside of leaves.Further symptoms of an advanced infection are thecessation of terminal growth, the disappearance ofaxillary buds and impairment of flower set.BLRV causes leaf yellowing, upward leaf-rolling and adecrease in the number of pods in field beans.MonitoringCheck the crop for the pest from May to July. If there is a light or generaldistribution and humid weather, or if breeding colonies are evident, controlmeasures are generally warranted.AHDB Aphid News provides information on aphid migration.ThresholdsCombining peas: 20% or more of plants infested at early flowering.Vining peas: 15% or more of plants infested.Field beans: None established.It should be noted that virus transmission can occur even with low aphid numbers.It is recommended that, if crops are in high-risk areas for viruses, aphids should becontrolled as soon as colonies appear, particularly if this occurs before flowering.There is no need to treat combining peas if they have been infested after thedevelopment of the fourth pod-bearing node.Non-chemical controlAvoid growing peas or beans in fields with nearby concentrations of clover orlucerne.Predators, such as ladybirds and hoverfly larvae, may help control pest populationsbut the presence of hoverfly larvae can contaminate vining peas. Other naturalenemies include spiders, fungal pathogens and parasitoids.Virus transmission risk can be minimised by ensuring that seed stock is free ofPSbMV.Insecticide resistanceNone known.63Pests: Bugs and aphidsPests: Bugs and aphids64

Peach–potato aphid (Myzus persicae)Peach–potato aphid (Myzus persicae)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beans✔ Sugar beet✔ Lettuce© ADASPeach–potato aphids© Rothamsted Research LtdPeach–potato aphidsImportanceThe peach–potato aphid is an important pest ofpotatoes, oilseed rape, vegetable brassicas, sugarbeet and lettuce. Transmission of viruses can causeserious economic damage but only heavy infestationscause direct feeding damage.This aphid is the most important vector of turnipyellows virus (TuYV), potato leaf roll virus (PLRV),potato virus A (PVA) and potato virus Y (PVY). It alsotransmits cauliflower mosaic virus (CaMV), beetyellows virus (BYV), beet chlorosis virus (BChV) andbeet mild yellowing virus (BMYV). The average yieldloss from TuYV in oilseed rape is 15% but it can be ashigh as 30%.Risk factorsIn potato and vegetable crops, infestations can bemore severe if overwintered brassica crops (or otheroverwintering hosts) are in neighbouring fields. Sugarbeet and oilseed rape can be a source of infestationfor vegetable brassicas and lettuce.Greater numbers of overwintering adults will survive ifwinter conditions have been mild. This is likely to leadto a larger and earlier spring migration and a greaterlevel of virus spread in early sown crops.In years with a smaller spring migration and largersummer migration, late-sown crops are at higher riskfrom virus transmission. The spring migration is oftenreduced in northern parts of the UK, due to coolerwinters.In oilseed rape, early sown winter crops tend to be atgreatest risk during warm autumns, while later-sownspring crops tend to be at greater risk after mildwinters.A close relationship has been found betweentemperatures in winter and early spring and theincidence of virus yellows in sugar beet at the end ofAugust in the absence of seed treatment.Life cycle123Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 1Asexual females overwinter in brassica and herbaceous crops and weeds. Asmall proportion of eggs overwinter on peach and nectarine trees. Coldweather reduces survival of mobile stages.Adults migrate to, and infest, a range of summer crops, including potato.They can multiply extremely quickly, with populations usually peaking inearly to mid-July. A further, smaller, peak occasionally occurs in lateAugust/September.In mild autumns, adults infest oilseed and vegetable brassicas, transferringviruses.Identification and symptomsThe wingless peach–potato aphid is medium-sizedand pale green to pink or almost black. The wingedform is a similar size but has a black central abdominalpatch on the upper surface with a pale underside.In oilseed rape, TuYV infection doesn't usually showuntil late spring/early summer, appearing as purpletingeing of leaf edges and pods, easily mistaken forfrost damage, nutrient deficiency or other stresses.In vegetable brassicas and lettuce, the peach–potatoaphid is a contaminant, can transmit viruses and, incases of severe infestation, may cause severedistortion of the plant.In sugar beet, beet yellowing virus symptoms arecharacterised by diffuse chlorotic patches on matureleaves, which expand and coalesce. Leaves may besubject to infection by secondary pathogens, such asalternaria. Leaves also become thickened and brittle,snapping crisply when broken.3© Dewar Crop ProtectionDifferent colours ofpeach–potato aphid© Dewar Crop ProtectionTurnip yellows virussymptoms65Pests: Bugs and aphidsPests: Bugs and aphids66

Peach–potato aphid (Myzus persicae)Peach–potato aphid (Myzus persicae)© The James Hutton InstitutePotato virus Y leafsymptoms© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightPotato leaf roll virussymptoms© BBROSymptoms of beetyellowing virus (top leaf)and beet mild yellowingvirus (bottom leaf)In potato, PVY infections caused by aphids result inleaf drop streak, where lower leaves develop blackstreaks on their underside veins and eventuallycollapse, hanging off the stem by a thread. Youngerleaves may develop necrotic spotting.Aphid-vectored PLRV infections result in the marginsof young leaflets rolling upwards and inwards, apattern more pronounced at the leaflet base. Infectedleaves may also develop a purple discolouration.Symptoms of secondary (tuber-borne) infections ofthese viruses may differ from the primary infectionsdescribed above.PVA infections usually cause mild mosaic symptoms.MonitoringAHDB Aphid News provides information on aphidmigration.There is a tool on the Potato Council website(www.potato.org.uk/online-toolbox) where you canbe alerted when the first peach–potato aphid is foundin a chosen region and when numbers exceed a giventhreshold.BBRO maintains a network of yellow water pans inthe sugar beet growing areas and records the numberof peach–potato aphids found weekly.ThresholdsFor sugar beet, apply a foliar insecticide when onegreen wingless aphid per four plants is found. Thisincreases to one green wingless aphid per plant onceat the 12 leaf stage.© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightPotato virus YsymptomsNo satisfactory thresholdsexist for other crops. Ifaphids are present, theyshould be assumed to becarrying virus.Non-chemical controlNatural enemies include parasitic wasps, ladybirds, predatory flies, spiders, groundbeetles, rove beetles, lacewings and insect-pathogenic fungi. Providing habitatsthat encourage the presence of these may help control aphid numbers. They maynot be effective in preventing virus transmission, as this can occur even at lowaphid densities.Using seed potato certified by the British Seed Potato Classification Schemereduces the virus risk and its subsequent spread by aphids. Potato varieties differ intheir susceptibility to aphid infestation and virus infection. Seek expert advice onwhich variety to choose if the crop is in a high-risk area.Early sowing of sugar beet can mean it is less likely to be affected, as older leavesare less palatable to the aphids.Insecticide resistanceThere are three different mechanisms of insecticide resistance in peach–potatoaphid in the UK. Neonicotinoid resistance has been discovered in southernmainland Europe but has not yet been detected in the UK.Chemical group ActivesOrganophosphates ChlorpyrifosDimethoateCarbamatesPyrethroidsPirimicarbBeta-cyfluthrinLambda-cyhalothrinAlpha-cypermethrinCypermethrinZeta-cypermethrinDeltamethrinEsfenvalerateTau-fluvalinateResistanceMechanism: elevatedcarboxylesterase.Resistance has fallen substantiallyfollowing a decline in the use oforganophosphates against aphids.Mechanism: modifiedacetylcholinesterase (MACE).Resistance is common andwidespread, with more than 80%of peach–potato aphids nowresistant.Mechanism: knockdown resistance(kdr).Two forms exist: kdr and amore potent variant termed superkdr.kdr resistance is currently rare;however, super-kdr resistance iscommon and widespread.The majority of peach–potatoaphids in the UK at present carryboth super-kdr resistance topyrethroids and MACE resistanceto pirimicarb.67Pests: Bugs and aphidsPests: Bugs and aphids68

Potato aphid (Macrosiphum euphorbiae)Crops affectedCerealsOilseeds✔ Vegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beans✔ Sugar beet✔ LettuceImportanceThe potato aphid is widespread most years and rarelyoccurs in epidemics. It is usually the commonestaphid species found on potato and can persist lateinto autumn.Yield reductions are caused as a result of sap-feedingand, especially, through the transmission of viruses,such as potato virus Y (PVY) and potato leaf roll virus(PLRV).On potato, this aphid tends to multiply on the flowersand shoot tips and even moderate numbers canproduce appreciable yield reductions.Potato aphid may infest vegetable brassicas andlettuce but it is generally a contaminant rather thancausing severe damage to plants. Sugar beet does not usually suffer from directfeeding damage but potato aphid can transmit beet mild yellowing virus (BMYV)and beet yellows virus (BYV), although less efficiently than peach–potato aphid.Risk factorsDamage in potatoes is greatest when aphid numbers peak after mid-July. Risk ofvirus transmission in sugar beet is greater in crops (without insecticide seedtreatments) that have fewer than 12 true leaves; older crops become unpalatable.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1Wingless adults and immature stages overwinteron weeds, potato sprouts, rose and protectedlettuce.2 Winged forms migrate to summer crops.3 Wingless forms feed and reproduce on the crop.41 2 4 51If heavy infestations occur, a further migration iscommon.5 A small autumn migration may occur.3© ADASAdult potato aphidPotato aphid (Macrosiphum euphorbiae)Identification and symptomsAdult potato aphids are large, relative to other aphid species, with wingless formsbeing 2.5–4 mm long. They have a pear-shaped green to pinkish-red body with adark stripe running down the back. They have long legs, a cauda (a finger-shapedstructure at the rear) and antennae at least as long as the body. Winged adults havea yellowish-brown head and green thorax.When infestations on potato are heavy, the feeding can result in ‘false top roll’symptoms (upper leaves roll). This can be distinguished from PLRV symptoms as itusually occurs earlier in the summer, has a patchy in-field distribution and is usuallyfound with the aphids or their cast skins.PVY infections caused by aphids result in leaf drop streak, where lower leavesdevelop black streaks on their underside veins and eventually collapse, hanging offthe stem by a thread. Younger leaves may develop necrotic spotting.Aphid-vectored PLRV infections result in the margins of young leaflets rollingupwards and inwards, particularly at the leaflet base. Infected leaves may develop apurple discolouration. Symptoms of secondary (tuber-borne) infections of theseviruses may differ from the primary infections described above.In sugar beet, beet yellowing virus symptoms are characterised by diffuse chloroticpatches on mature leaves, which expand and coalesce. Leaves may be subject toinfection by secondary pathogens, such as alternaria. Leaves also becomethickened and brittle, snapping crisply when broken.MonitoringAHDB Aphid News provides information on aphid migration. BBRO maintains anetwork of yellow water pans in the sugar beet growing areas and records thenumber of potato aphids found weekly.ThresholdsPotatoes: None established. Treat if aphid numbers start to increase rapidly onvarieties known to be susceptible to 'false top roll'.Non-chemical controlNatural enemies include parasitic wasps, ladybirds, predatory flies, spiders, groundbeetles, rove beetles, lacewings, and insect-pathogenic fungi. Providing habitatsthat encourage the presence of these may help control aphid numbers. They maynot be effective in preventing virus transmission, as this can occur even at lowaphid densities. Early sowing of sugar beet can mean it is less likely to be affected,as older leaves are less palatable to the aphids.Insecticide resistanceNone known.69Pests: Bugs and aphidsPests: Bugs and aphids70

Rose–grain aphid (Metopolophium dirhodum)Rose–grain aphid (Metopolophium dirhodum)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceWhere populations of this pest exceed thresholdlevels, their feeding can cause yield losses of up to4 t/ha but 0.25–1 t/ha is more usual.Rose–grain aphid is unimportant as a vector of barleyyellow dwarf virus (BYDV) because it spends thewinter as an egg on roses.Risk factorsAll cereals are at risk, although winter barley is lessaffected due to its earlier senescence.Drought-affected crops or those damaged by otherpests and diseases also suffer greater impact due tolower reserves of soluble stem carbohydrates.Increased risk is also associated with dry, settled weather during early grain filling.Rose–grain aphids tend to be a problem after hard winters when both grain aphidsand their natural enemies are scarce. The rose–grain aphid is susceptible to all thenatural enemies of the grain aphid. If the grain aphid and its natural enemies arepresent, it is more difficult for an infestation of rose–grain aphid to becomeestablished.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3 4 151 Eggs overwinter on wild and garden roses.2 Winged forms migrate to crops.3 Feeding on crops and grasses.4 Very frost-hardy eggs laid on wild and garden roses.5 Adults can overwinter on grasses.© ADASRose–grain aphid5Identification and symptomsThe rose–grain aphid is medium-sized and light greenor, rarely, pink. Green varieties have a dark, brightgreen stripe down the centre of their back.Rose–grain aphids are only ever found on the leavesand never on the ears.Only very severe infestations produce visiblesymptoms in crops. Infested leaves turn yellow andsenesce prematurely.MonitoringCheck for aphids on the lower leaves at about thetime the cereals are coming into ear. Individuals alsocollect on the top leaves in the later growth stages.They do not move to the ear.Refer to AHDB Aphid News for information onmigration.ThresholdsBefore GS61: Half of tillers infestedGS61 to two weeks before end of grain filling: Twothirdsof tillers infested from stem extension to flagleafemergence, or if more than 66% of tillers areinfested and numbers are increasing for the periodfrom flowering to watery ripe.Non-chemical controlAgri-environment habitats comprised primarily ofgrasses, such as buffer strips, can also provideharbourages for aphids; on the other hand, thesepopulations also help support their parasitoids throughthe winter. Wildflower strips with a more diversegrass mixture are less likely to harbour pests and willencourage parasitoids and hoverflies. Other naturalenemies include lacewings, ground beetles, soldierbeetles, rove beetles, ladybirds, spiders and fungaldiseases.Insecticide resistanceNone known.© Dewar Crop ProtectionRose–grain aphids© ADASRose–grain aphids© ADASRose–grain aphids71Pests: Bugs and aphidsPests: Bugs and aphids72

Tarnished plant bug (Lygus rugulipennis)Tarnished plant bug (Lygus rugulipennis)Crops affectedCerealsOilseedsVegetable brassicasPotatoes✔ CarrotsAlliumsPeasField beans✔ Sugar beet✔ LettuceLife cycle12Adults overwinter on evergreen foliage and inleaf litter.Adults emerge in March/April and begin feedingon plant tissues.3 Females lay eggs in plant tissue.4Nymphs develop through six instars and adultsare produced by July.5 Adults feed.6ImportanceThe tarnished plant bug is a type of capsid bug. Theadults and nymphs feed on leaves, buds and fruits ofsusceptible plants (carrot, celery, lettuce and othervegetables), seriously reducing marketability.It can also damage sugar beet, causing distortion ofthe growing point, multiple crowning and poorlyyielding plants.Other species of capsid may also cause damage.Risk factorsThe nature of the surrounding vegetation in terms ofprovision of alternative hosts and an overwinteringsite may be a risk factor.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 4 13 5Another generation is produced inAugust/September.6© BBROAdult capsid bugIdentification and symptomsAdult bugs are 5–6 mm long, oval-shaped andbrownish-green with dark markings. They usuallyappear to be ‘tarnished’. They have a small head witha pair of long, jointed antennae.Eggs are elongate and slightly curved. They areinserted into the tissues of terminal shoots, buds andfruits.The nymph is green with black spots on its thorax.Usually, the first signs of damage are small brownspots on young leaves. Because the area surroundingeach feeding site dies, affected plants fail to growproperly and plant parts become malformed.In summer, other species of capsid feed on the leafveins of older plants, causing puckering and yellowing.Close to the puncture site, the tissue is oftenblackened.MonitoringPheromone traps are available for monitoring adulttarnished plant bugs.Blue sticky traps are more effective than yellow stickytraps.ThresholdsNone established.Non-chemical controlTrap crops have been used successfully in strawberry,sometimes in conjunction with vacuuming the trapcrop to reduce infestations. Further research would beneeded to evaluate such approaches for fieldvegetables.Some variation in susceptibility between carrotcultivars was identified some years ago.Insecticide resistanceNone known.© Rothamsted Research LtdAdult capsid bug© Rothamsted Research LtdCapsid nymph© Rothamsted Research LtdCapsid bug damage© Rothamsted Research LtdCapsid bug damage73Pests: Bugs and aphidsPests: Bugs and aphids74

Willow–carrot aphid (Cavariella aegopodii ) Willow–carrot aphid (Cavariella aegopodii )Crops affectedCerealsOilseedsVegetable brassicasPotatoes✔ CarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceWillow–carrot aphid can affect carrot, celery, parsnipand parsley. Severe infestations can distort the foliageand stunt plants, killing them if they are very young.The aphid is also the vector of parsnip yellow fleckvirus and the two viruses that cause carrot motleydwarf disease. It can also transmit carrot red leafvirus, parsnip mosaic virus and celery mosaic virus.Risk factorsInsecticidal control of the aphids may have little impacton virus transmission. Willow–carrot aphid generallyoverwinters on willow trees. Dry sunny weather inlate May/June favours a large-scale migration to hostcrops but cold rainy weather inhibits it.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 4561Identification and symptomsThe adult wingless form is 1–2.6 mm long, green oryellowish-green, elongate oval and somewhatflattened. There are two tubes (siphunculi) at the rearend, which are swollen towards the tips. A smalloutgrowth is present above the tail. The winged formis darker and has a black patch on the upper surfaceof the abdomen.The aphids infest carrots at the cotyledon stage butcan also invade older plants. When many are present,the leaves may be discoloured, distorted andsometimes shiny from honeydew excretion. Theplants and ground below may become covered withcast skins.© University of WarwickWillow–carrot aphidsParsnip yellow fleck virus can cause stunted plants and blackening of the centralcore. Carrot motley dwarf disease produces a yellow mottling of the leaves andstunts the plants.Feeding damage may be confused with damage due to carrot fly and sometimesdrought stress, which produces similar foliage symptoms.1The aphid overwinters mainly as eggs, which arelaid around the buds of willow.2 Eggs hatch.3 The aphids feed and reproduce on the willow.453Winged forms are produced and migrate tocarrot and other host plants over a five to sixweek period, usually with a peak in early June.Late seasons can delay migration for two to threeweeks.Further winged generations disperse to wildhosts.© Dewar Crop ProtectionMonitoringAHDB Aphid News provides information on winged aphid migration.A day-degree forecast has been developed to predict the start of the migrationfrom willow to carrot and other host plants. More information is available in theHDC Pest Bulletin.ThresholdsNone established.Non-chemical controlThe mobile forms are attacked by a number of natural enemies, including ladybirds.Young aphids may be parasitised by certain species of wasp, whose larvaeeventually kill the aphid, which forms a hard gold-coloured ‘shell’ known as a‘mummy’. To date, biological control with natural enemies has not been evaluatedin the UK but the efficacy of several biopesticides is being evaluated.6Winged aphids migrate to willow to mate and layeggs.Winged willow–carrotaphidIn warmer locations, a small proportion of the population may overwinter asmobile stages on crops in field storage or on wild hosts and produce coloniesearly the following spring.Insecticide resistanceNone known.75Pests: Bugs and aphidsPests: Bugs and aphids76

Minor and/or emerging pestsMinor and/or emerging pestsPotato leafhoppers (Edwardsiana flavescens, Empoasca decipiens,Eupterycyba jucunda and Eupteryx aurata)Crops affectedCerealsOilseedsVegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beansSugar beetLettuceFour species of leafhopper commonly attack potatobut they seldom cause economic damage.Leafhoppers are around 5 mm long, with elongatedyellow or green bodies and they tend to fly or jumpaway when disturbed.The potato leafhoppers are common inhabitants ofhedgerows, moving into the crop in early summer tofeed on the underside of leaves. Pale, slender eggsare laid on stems and leaf veins. Several generationscan be completed in a year.Feeding causes pale speckling of the leaves, while theinjection of their saliva into the phloem causes'hopperburn', a yellowing/browning of the foliage.Severe cases can result in brown, wilting and dyingleaves.© Bayer CropScience © Bayer CropSciencePotato leafhopperPotato leafhopper77Pests: Bugs and aphidsPests: Bugs and aphids78

Further informationAlerts and bulletinsAHDB Aphid News: This alert service provides weekly updates on regional aphidactivity during key times of the year. www.hgca.com/pestsHDC Pest Bulletin: Sponsored by Syngenta and hosted on the Syngenta website,this bulletin aims to provide growers with topical and valuable agronomyinformation throughout the growing season.www3.syngenta.com/country/uk/en/AgronomyTools/HDCPestBulletinHDC PublicationsAvailable at www.hdc.org.ukHDC Factsheet 10/14: Cabbage whitefly (2014)HDC Factsheet 35/12: Minor pests of Brassicas (2012)HDC Factsheet 03/12: Pea aphid control (2012)HDC Factsheet 21/11: Virus diseases of carrots (2011)HGCA PublicationsAvailable at www.hgca.com/publicationsHGCA Information Sheet 32: Controlling aphids and virus diseases in cereals andoilseed rape (2014)HGCA Research Review 77: Implications of the restriction on the neonicotinoids:imidacloprid, clothianidin and thiamethoxam on crop protection in oilseeds andcereals in the UK (2013)Potato Council PublicationsAvailable at www.potato.org.uk/knowledge-hubGuidelines for preventing and managing insecticide resistance in aphids onpotatoes (2011)Information from other organisationsFera Plant Disease Factsheet: Aphid transmitted viruses of potato (2009)APHMON – National yellow water trap data www.aphmon.fera.defra.gov.uk79Pests: Bugs and aphids

Pests:Flies, thrips andsawflies

Contents – Pests: Flies, thrips and sawfliesSpeciesPageBean seed flies (Delia platura and Delia florilega) 81Beet leaf miner (Pegomya hyoscami) 83Brassica leaf miner (Scaptomyza flava) 85Brassica pod midge (Dasineura brassicae) 87Cabbage root fly (Delia radicum) 89Carrot fly (Psila rosae) 93Frit fly (Oscinella frit) 95Gout fly (Chlorops pumilionis) 97Leatherjackets (Tipula paludosa and Tipula oleracea) 99Onion fly (Delia antiqua) 101Orange wheat blossom midge (Sitodiplosis mosellana) 103Pea midge (Contarinia pisi ) 105Saddle gall midge (Haplodiplosis marginata) 107Swede midge (Contarinia nasturtii) 109Thrips 111Turnip sawfly (Athalia rosae) 117Wheat bulb fly (Delia coarctata) 119Yellow cereal fly (Opomyza florum) 121Minor/emerging pests 123Allium leaf miner (Phytomyza gymnostoma) 123Cereal stem sawfly (Cephus pygmaeus) and leaf sawflies 124Yellow wheat blossom midge (Contarinia tritici ) 124Further information 125

Flies (Diptera)Flies are, typically, the most numerous insects found on farmland and, although someare crop pests, others help perform important functions such as helping control croppests (see page 185), recycling organic matter and acting as food for farmland birds.Life cycleThere are four stages to the fly life cycleand the length of each stage willdepend on the species.HeadHaltere(balancer)WingPupaAdultLarvaEggsAntennaeThoraxMouthpartsLegsAbdomenDefining featuresFlies are defined by having only a singlepair of wings. Fly larvae are mostly leglessmaggots.ThoThrips (Thysanoptera)Thrips, commonly known as thunderflies, arenot true flies. They are tiny, slender insects withfringed wings.Sawflies (Hymenoptera: Symphyta)Sawflies are not true flies: they are relatedto bees, wasps and ants. The adults looksimilar to wasps but are distinguished bya broad connection between theabdomen and thorax (unlike the ‘waspwaist’ of other species of Hymenoptera).Sawfly larvaThoracic true legsAbdominal prolegsThe larvae look like caterpillars but havesix or more pairs of prolegs on theabdomen, whereas caterpillars have fivepairs or fewer with the first twoabdominal segments legless. Sawflylarvae also have a smooth head capsulewith distinct small black eyes.Butterfly larva (caterpillar)Pests: Flies, thrips and sawflies80

Bean seed flies (Delia platura and Delia florilega)Crops affected✔ CerealsOilseeds✔ Vegetable brassicasPotatoesCarrots✔ Alliums✔ Peas✔ Field beansSugar beet81Lettuce© University of WarwickBean seed fly adultLife cycle12Bean seed flies overwinter as pupae in thesoil.Flies start to emerge and, after feeding andmating, the female lays eggs just below thesoil surface, generally singly. They may layas many as 40 eggs in a day. There isgenerally a period of several days before afurther batch of eggs is laid.Pests: Flies, thrips and sawfliesImportanceDamage can be localised and sporadic, even thoughthe adult flies are common.In beans, the most serious damage is caused in thespring. Usually, the first sign of damage is the patchyemergence of seedlings and it is impossible to controlan infestation at this point.Seeds of other crops (eg alliums and sweetcorn) arealso vulnerable, especially if sown in later spring orearly summer.Risk factorsFemales prefer to lay eggs in freshly disturbed soil,especially where there are residues of vegetablematter or where farmyard manure has been applied.The presence of plants is not required for bean seedflies to lay eggs.Any factors that slow down the speed of germinationand shoot vigour increase the risk of damage, inparticular, low temperatures and excessively deepsowing. High levels of moisture are also thought toincrease the risk of damage.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec134In the absence of a suitablehost plant, the larva is ableto complete development byfeeding on decomposingorganic matter.The larvae pupate in the soilat varying depths.Bean seed flies can complete between three and six generations per year,depending on the ambient temperature.234Bean seed flies (Delia platura and Delia florilega)Identification and symptomsThe adult is a small greyish-black fly, 4–5 mm long. Theegg is white, elongated and about 1 mm long. Thelarva is a white maggot, which reaches 5–8 mm inlength when fully grown and the pupa is reddishbrownand about 5 mm long.The larvae feed on the buried seed or the cotyledonsof the seedling before sprouting. Damage to all cropsis manifested mainly as patchy emergence ofseedlings or seedling death. When runner or Frenchbeans are very severely attacked, the growing pointmay be lost, seedlings then emerge in a twistedcondition known as ‘snake head’ and soon die.Damage to onions may appear as poor emergence, since the larvae usually attackthe seedling between germination and emergence. Plants are often killed at the‘loop’ or ‘crook’ stage.Damage in cereals can be hollowed grains. Newly transplanted cucurbits may bedamaged soon after planting. The plants collapse completely, often within days ofbeing transplanted. Later attacks cause plants to wilt during dry weather. Onasparagus, the attacked spears are deformed, often split, and have a bitter taste.MonitoringAdult bean seed flies (both sexes) can be monitored using coloured sticky traps orwater traps. Yellow, blue and white traps are all effective but white traps and certaincolours of blue may be preferred. Water traps are also suitable for monitoring thisspecies.ThresholdsThere are no thresholds to relate the risk of crop damage to numbers of fliescaptured in traps but trap captures do indicate when bean seed flies are active andhow numbers change during the season.Non-chemical controlThe presence of organic matter in the soil is an important stimulus for egg laying.Properly burying any organic debris from previous crops should reduce risk.Natural controls are likely to include generalist predators, such as certain species ofbeetle, spiders, insect-pathogenic fungi and parasitoids (beetles and wasps). Twospecies of Aleochara (rove beetle, see page 178), which can be both pupal parasitoidsand predators of eggs and larvae, have emerged from bean seed fly pupae.Insecticide resistanceNone known.© University of WarwickBean seed fly lifestagesPests: Flies, thrips and sawflies82

Beet leaf miner (Pegomya hyoscyami)Beet leaf miner (Pegomya hyoscyami)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuceImportanceIn recent years, there has been an increase in theincidence of late beet leaf miner and control optionsare very limited. Extensive damage can affect theplant's photosynthetic ability. In large numbers, theycan almost defoliate whole plants.Risk factorsThe first generation is the most damaging, especiallyin late-sown crops with low leaf area. Latergenerations can be numerous but damage is lessserious because they inhabit outer leaves and oftencoincide with periods of rapid growth, offsettingeffects.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec123 541Identification and symptomsThe eggs are white, patterned and approximately1 mm long. They are found on the underside of beetleaves in groups of between two and ten.Larvae are translucent, whiteish to pale green and6–8 mm long. They are not generally seen but theirpresence can be detected by the appearance ofmines and blisters on the beet leaf. Symptoms ofheavy infestations can resemble those of bacterial leafblight.The pupae are brown, oval and approximately 5 mmlong.MonitoringEggs can readily been seen with the naked eye ingroups on the underside of leaves. If mines are seenin the leaves, they should be checked to see ifthresholds have been reached.Timing of sprays is critical for good control becausethe larvae are hard to kill once inside the leaf. Theoptimum timing is at egg hatch.© BBROBeet leaf miner eggs© Rothamsted Research Ltd1 Beet leaf miner overwinters in the soil as pupae.2 The first flies emerge throughout April. Aftermating, the females lay eggs on the underside ofbeet leaves.3 Eggs hatch after 3–10 days and the larvae enterthe leaf and feed between the two leaf layers. Themines join and blister as the larvae grow. Afterabout 10–15 days, the fully grown larvae leavethe leaf and fall to the ground, where theypupate.4 There can be another one or two overlappinggenerations.5 There can be another one or two overlappinggenerations.© Rothamsted Research LtdBeet leaf miner larvaThresholdsThe threshold for treatment is when the number ofeggs and larvae exceeds the square of the number oftrue leaves. For example, a plant with four true leaveswould need a population of 16 (4x4) or more eggs andlarvae to warrant treatment.Non-chemical controlThe third generation is most susceptible to predationby natural enemies, such as parasitic flies (eg Opiusnitidulator). The decision of whether to apply lateapplications of insecticide should balance thelikelihood of success against the risk of harming thesenatural enemies.Insecticide resistanceNone known.Beet leaf minerdamage© BBROBeet leaf minerdamage83Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies84

Brassica leaf miner (Scaptomyza flava)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© Dewar Crop ProtectionBrassica leaf miner lifestagesLife cycle1 Brassica leaf miner overwinters as pupae inthe soil.2 Adults are generally most abundant inSeptember, although local peaks of activitycan occur in July or August. Females lay eggsin punctures made within the lower surface ofthe leaf and can lay more than 300 eggs.85 Pests: Flies, thrips and sawfliesImportanceAlthough the brassica leaf miner is a native species of fly,it was not regarded as a pest of major economicimportance on vegetable brassicas until recently.Damage to brassica salad crops, such as rocket andtatsoi, has been particularly severe.Crop damage is caused by adult females, which puncturethe leaf surface with their ovipositor to lay eggs, and bythe larvae, which produce the characteristic white'corridor-blotch' mines when feeding between the upperand lower surfaces of the leaf.In oilseed rape, despite the unsightly mines, it is unlikelythese pests will ever justify insecticide treatment. Ingeneral, it is only the first developing true leaves that areinfested and these usually die during the winter.Oilseed rape can also be attacked by cabbage leaf miner(Phytomyza rufipes). This mostly mines the leaf petiolesand is often undetected. Since only the outer leaves areaffected and these usually die during winter, cabbage leafminer is not regarded as an economic pest and control isunnecessary.Risk factorsThere is no definitive information on the number ofgenerations completed by this species in the UKalthough, according to the literature, adults aregenerally most abundant in September.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12 1343 In the UK, mines are typicallyseen between July andOctober.4 Larvae usually drop to theground to pupate butsometimes a separatepupation mine is used.Brassica leaf miner (Scaptomyza flava)Identification and symptomsThe adult is pale brown with faint stripes on the thoraxand red eyes. The wings are about 50% longer thanthe head and thorax combined. It is about 3 mm longwith a wing span of 6 mm.Eggs (0.3–0.4 mm long, 0.2 mm wide) are laid singlybut quite close to one another.The larva is a cylindrical maggot, which becomesgreenish in colour and is 0.4–5 mm long.The pupa is brown, about 3 mm long, and is generallyfound in the soil.The hatching larva initially moves towards the mid-rib,creating a long corridor. Once at the mid-rib, the larvaforms a large irregular white/yellow blotch in the upperleaf surface with occasional excursions into the leafblade. Several larvae may be present in the samemine and, if the leaf is small, the entire leaf may beoccupied. In smaller leaves, the mine lies in the centreof the leaf and often touches the petiole, while inlarger leaves the mine is to one side of the mid-rib.Frass (droppings) is usually deposited in green clumpsnear the margin of the mine.MonitoringYellow water traps or white sticky traps can be used tomonitor adults. No forecasting systems have beendeveloped.ThresholdsNone established.Non-chemical controlVegetable brassicas could be protected by coveringthem with insect-proof netting at times when theadult flies are active and laying eggs.© University of WarwickBrassica leaf minerdamage© University of WarwickBrassica leaf minerdamageInsecticide resistancePopulations have recently developed resistance to pyrethroid insecticides and HDCfundedresearch (FV 376) suggested that brassica leaf miner has become a moreimportant pest of cruciferous crops as a result.Pests: Flies, thrips and sawflies86

Brassica pod midge (Dasineura brassicae)Brassica pod midge (Dasineura brassicae)Crops affectedCereals✔ OilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycle1 Larvae overwinter in the soil.2 Adults emerge.34ImportanceThe brassica pod midge lays its eggs in developingpods in the holes left by seed weevils (see page 19).Larvae feed within the pod, causing swelling and,eventually, pod burst. With damage greatest onheadlands and affected pods very conspicuous, theimpact of this pest on yield can be overrated.However, spring oilseed rape yields can be severelyreduced.Risk factorsThe largest yield losses often occur in small narrowfields. The adult midge is a weak flyer, so crops onheadlands are more exposed to immigrant midges.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 23Adults mate and fly to oilseed rape, where they lay eggs in cabbage seedweevil holes and damaged areas of the plant.4Larvae feed, pods swell and burst. Larvae drop to the soil. Some develop, togive second and third generation adults.1Identification and symptomsThe adults are small, dark orange midges that appearduring flowering. To lay eggs, the midge is dependenton the pod being previously damaged – usually by thefeeding and egg-laying punctures made by thecabbage seed weevil.Numerous minute eggs are laid in clusters inside thepod, giving rise to large numbers of larvae, which feedon the inner walls of the developing pods. At maturity,the larvae are white, with no legs or distinct head, and2 mm long, at which point they drop to the soil topupate.Infested pods yellow and split prematurely,occasionally becoming swollen and distorted (‘bladderpods’). This results in a complete loss of seed.MonitoringControlling cabbage seed weevil is the most effectivemeans of avoiding damage from the brassica podmidge.ThresholdsControl of brassica pod midge is dependent on thecontrol of cabbage seed weevil. Thresholds forcabbage seed weevil are 0.5 weevils per plant in thenorth of the UK and 1 weevil per plant elsewhere.See page 19.Non-chemical controlBlocking oilseed rape fields and rotating the croparound the farm helps reduce the impact of immigrantpests.Several wasp parasitoids, including Omphale clypealisand Platygaster subuliformis, may attack pod midge,killing up to 75% of larvae. Other natural enemiesinclude spiders, ground beetles, rove beetles andpredatory flies.Insecticide resistanceNone known.© ADASBrassica pod midgelarvae© ADASBrassica pod midgesymptoms© Image courtesy of The Food andEnvironment Research Agency (Fera),Crown CopyrightBrassica pod midgesymptoms87Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies88

Cabbage root fly (Delia radicum)Cabbage root fly (Delia radicum)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© Jon OakleyAdult cabbage root fly© University of WarwickImportanceCabbage root fly is present throughout the UK andcan cause damage to cabbage, cauliflower, broccoli,Brussels sprout, kale, Chinese cabbage, swede, turnipand radish. It can also attack oilseed rape but isgenerally considered a minor pest.If uncontrolled, almost 100% of plants may beinfested but yield losses will depend on the impact ofdamage on plant growth and quality. Good levels ofcontrol are particularly important where the root is themarketed crop (swede, turnip, radish).Plants with low levels of root damage usually survive,particularly if conditions are wet or irrigation is used,but this may affect uniformity within the crop,increasing the number of passes required at harvest(eg for cauliflower).In certain circumstances, cabbage root fly larvae mayalso infest broccoli florets, Brussels sprout buttonsand the foliage of Chinese cabbage.Risk factorsYoung plants are most likely to be killed by cabbageroot fly larvae, whereas older plants generally have asufficiently large root system to be able to toleratemoderate to high levels of infestation, depending onspecies. Newly emerged drilled crops and recentlytransplanted module-grown plants are, therefore, likelyto be most susceptible.Plants where the marketable part of the plant isdamaged (root crops, Brussels sprout buttons,broccoli florets, Chinese cabbage) may be at risk of‘cosmetic’ damage by one or more generations of thepest.In oilseed rape, crops that have emerged before theend of August are most at risk of attack.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 52 3 6 7 81 Pupae from late second and early third generations overwinter in soil.2 Adult flies emerge and feed/mate.3 Eggs are laid (first generation).4 Larvae feed.5 Pupae present in soil.6 Eggs are laid (second generation).7 Eggs are laid (late second generation, early third generation).8 Eggs are laid (third generation).The life cycle is driven by temperature, so activity will be earlier in warmyears/locations. In the UK, depending on temperatures, there are generally two tothree generations of adults in the south and only two generations in the north.There are some areas of the UK where a proportion of the cabbage root fliesemerge later in the spring than would be expected. These are called ‘late-emerging’flies and they are genetically different from ‘early emerging’ flies. Relatively largenumbers of late-emerging flies occur in some parts of Devon and south-westLancashire.41Cabbage root flydamage89Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies90

Cabbage root fly (Delia radicum)Cabbage root fly (Delia radicum)© University of WarwickCabbage root fly adult© University of WarwickCabbage root fly larvae© University of WarwickIdentification and symptomsThe adult flies are greyish-brown and resemble smallhouseflies. The male is 5–6 mm long and the female6–7 mm.The eggs are white, about 1 mm long and are laidmainly in the soil around the stems of brassica plants.The larva is more or less transparent, tapering andlegless with a reduced head. The mouthparts look likeblack hooks. Fully grown larvae are 5–8 mm long.The pupae are dark brown and barrel-shaped, withsmoothly rounded sides and most are found 8–12 cmbelow the soil surface.The larvae feed primarily on the roots of brassicaplants, although they sometimes feed on the aerialparts. Where most of the root system has beendamaged, the plants may wilt or even die. Whenplants have large root systems, damage may not beapparent until the plant is harvested. Damage to theaerial parts is generally not apparent until the plantsare harvested and damaged produce may be difficultto identify even at this stage.MonitoringAdult flies can be captured in yellow water traps ormore specialised traps that release a semiochemical(related to the distinctive chemical compoundsproduced by brassica plants).The soil around plants can be sampled to determinethe presence of eggs.A weather-based forecast for the timing of egg layinghas been developed with HDC/Defra funding andoutputs are available to UK growers via the HDC PestBulletin.ThresholdsThere are no current validated thresholds for cabbageroot fly. Most vegetable brassica crops need to betreated prophylactically as once larvae haveestablished they are very difficult to control.Non-chemical controlFine mesh netting (crop covers) has been usedsuccessfully to prevent egg laying by female cabbageroot flies on susceptible crops (eg swede). Femaleflies can lay their eggs on or through the netting if ittouches the crop but the incidence of this seems tobe low.Other physical and cultural approaches (companionplanting, vertical fences, trap crops) have beeninvestigated but control is not as effective as the useof currently available insecticides or fine mesh netting.A range of natural enemies contribute to controllingbackground levels. These include two parasitoids,spiders, ground and rove beetles, and predatory flies(Muscidae).To date, biological control with predators or parasitoidshas not been commercially viable. There is evidencethat the use of insect-pathogenic nematodes orinsect-pathogenic fungi may be effective in certainsituations.There is no host plant resistance available at presentbut some crop types are more susceptible thanothers.Insecticide resistanceNone known.© University of WarwickCabbage root flieskilled by a fungus© University of WarwickCabbage root flydamage on swedeCabbage root fly larva91Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies92

Carrot fly (Psila rosae)Crops affectedCerealsOilseedsVegetable brassicasPotatoes✔ CarrotsAlliumsPeasField beansSugar beetLettuceLife cycle12Carrot flies overwinter as pupae or as larvae,which continue to feed on overwintered cropsand then pupate the following spring.The first generation of adult flies emerges inApril–May and most eggs are laid during May.3 Larvae feed and pupae are formed.45ImportanceCarrot fly is present throughout the UK. The larvaefeed on the roots of carrot and other susceptiblecrops, making tunnels (mines) as they grow. Whenthe carrots are small, the plants are killed; largerplants are made unmarketable through the presenceof even a few relatively superficial mines.Risk factorsCarrot fly adults do not disperse over great distancesso crops that are most at risk are those close tofields that were infested previously with carrot fly.Damage is likely to be greatest at the edges offields.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 23Adults emerge from mid-July onwards toproduce the overwintering generation.In warm locations, a third generation of adultsmay emerge in October–November. It is believedthat the progeny of these flies do not developsufficiently before the winter to cause furtherdamage.Carrot fly adultThe rate at which the carrot fly completes its life cycle is dependent ontemperature and more generations will be completed in warm locations. In theUK, depending on temperatures, there are two to three generations of adults inthe south and only two generations in the north.415© University of WarwickCarrot fly (Psila rosae)Identification and symptomsAdult carrot flies are 6–8 mm long, with two pairs ofiridescent wings. The body is black and shiny, the headis reddish-brown and the legs are yellow. The whitecolouredeggs are elongate (0.2 mm diameter,0.6–0.7 mm long). The larva is creamy white in colourand is 8–10 mm long when fully grown. The brownpuparium is about 5 mm long and 1.5 mm in diameter.The larvae first feed on the lateral roots of carrotplants and then proceed to burrow into the tap root asCarrot fly damagethey grow. With young plants, where most of the rootsystem has been damaged, plants may wilt or even die. When plants have largeroot systems, damage may not be apparent until the plant is harvested.MonitoringAdult flies can be captured on yellow/orange sticky traps. Orientating the traps atan angle of 45˚ to the vertical makes them more selective for carrot flies, whichland on the lower surface.A weather-based forecast for the timing of egg laying has been developed with HDC/Defra funding and outputs are available to UK growers via the HDC Pest Bulletin.ThresholdsNone established. Treatment timing will depend on whether the insecticide used istargeted at flies or larvae.Non-chemical controlCrop rotation and the separation of new crops from sources of carrot fly is a veryeffective method of managing carrot fly populations. Where feasible, delayingsowing of susceptible crops until after the first generation has laid most of its eggswill also suppress populations.Fine mesh netting (crop covers) has been used successfully to prevent egg layingby female carrot flies on susceptible crops. Other physical and cultural approaches(companion planting, vertical fences, trap crops) have been investigated but controlis not as effective as the use of currently available insecticides or fine mesh netting.To date, biological control with predators or parasitoids has not been commerciallyviable. There is evidence that the use of insect-pathogenic nematodes may beeffective in certain situations. Some cultivars are less susceptible to carrot flydamage than others but none have complete resistance.Insecticide resistanceNone known.© Dewar Crop Protection93Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies94

Frit fly (Oscinella frit)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceFrit fly is usually most damaging to late-sown cerealsafter grass and spring-sown oats. There are threegenerations of frit fly per year. The first generation isdamaging to winter cereals, grasses, maize and latesownspring oats. The second generation lays eggs indeveloping oat grains and the third lays eggs ongrasses and winter cereals.Risk factorsWinter crops are at most risk of damage, while springcrops usually only suffer damage if sowing has beendelayed or if crop growth is checked for other reasons.The risk of frit fly attack is greatest after grass leys orin areas in which grass is a common crop.Crops are most susceptible to shoot damage up to the four-leaf stage.From late July, emerging adults lay eggs on oat husks, which can lead to seriousdamage to the ears of spring oats. However, as these are only susceptible for ashort time, sowing crops early or choosing those that develop rapidly can narrowthe period of risk.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 4 61Frit fly (Oscinella frit)Identification and symptomsThe frit fly adult is small (about 1.5 mm long), shiny andblack. It rests in cold, wet weather but is active in fineconditions. The larva is a small, white maggot, about3 mm long when fully grown. The larvae are usuallyfound inside the damaged shoot. The pupa is protectedby a reddish-brown casing.© Bayer CropScienceFrit fly damageDamage in cereals is most evident as ‘deadhearts’, where the central leaf of theplant turns yellow, withers and dies, often falling out completely. Very young plantscan be killed. Older plants can produce several tillers in response to the death of themain shoot, although these may also be invaded. This leads to plants with a largenumber of weak shoots which produce poor yield and later-ripening grain. In oats,deadhearts can be mistaken for stem nematode damage, in which the base of theplant is also swollen and the leaves are pale, stunted and twisted.Spring oats may be damaged prior to ear emergence, which can lead to blind,withered spikelets. Adults hatching in July lay eggs on the ears of oats. The hatchinglarvae burrow into the husk to feed on the kernels. Damage to oat ears is difficult todetect and the blackened, thinned kernels can only be seen by opening the grains.In maize, severe damage can be seen as ragged leaves that are often torn intostrips. Mild damage is evident as neat rows of holes across leaves.MonitoringA risk assessment for winter cereals can be made by sampling the grass or stubblefor frit fly eggs/larvae before ploughing. Key monitoring takes place after fullemergence (see Thresholds).3 51 Larvae feed slowly in shoots of cereals and grasses.2 First generation adults emerge and lay eggs ongrasses and young cereals.3 Larvae burrow into the central shoot of young cereals.4 Second generation adults emerge and lay eggsbeneath oat husks and grasses.5 Hatching larvae feed on oat kernels.6 Third generation adults lay eggs on grasses instubble and early winter cereals.Because there are three generations per year, damagecan occur to crops at different times of the year and todifferent parts of the plant (shoots and grain).© Bayer CropScienceAdult frit fly© Bayer CropScienceFrit fly larvaeThresholdsExamine plants soon after full emergence. If more than 10% are damaged, aninsecticide is recommended.Non-chemical controlTo minimise damage to winter cereals, plough grass and leave it at least fourweeks before sowing. If there is no live buried grass, the frit fly larvae will soon diefrom starvation. For spring oats, early sowing is the best method of avoiding attack.There is only a narrow window of opportunity to control frit fly in spring cerealsbefore they burrow into the crop. If damage is seen, it is too late to treat withinsecticides. Any husbandry, such as rolling, that encourages rapid establishmentand growth will help to minimise frit fly damage. Natural enemies include spiders,ground beetles, rove beetles, predatory flies and many parasitoid species.Insecticide resistanceNone known.95Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies96

Gout fly (Chlorops pumilionis)Gout fly (Chlorops pumilionis)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© ADASImportanceGout fly is present across the UK and is an occasionalminor pest of cereals. It can damage wheat, barleyand triticale. There are two generations per year. Thefirst lays eggs in May/June and the second lays eggsin late August/September.In autumn-sown crops, yield losses can range from0.25 tonnes/ha to, in exceptional circumstances, totalcrop failure if half or more of the crop is damaged.Winter damage kills affected tillers and any stilldependent on the mother plant. At lower levels ofincidence, unaffected tillers with developed crownroot systems can compensate for damage andsurvive.Shoots damaged by spring generations of gout flylose 30% of grain yield on average but this can rise toup to 50% yield loss in late-sown spring crops.Identification and symptomsAdult flies are yellow with black markings and4–5 mm long. Minute, creamy white torpedo-shapedeggs are laid on leaves close to the central shoots,usually one per shoot. Larvae are legless, translucentwhiteand lack a distinct head. When fully grown, theyare yellowish-white and 5–6.5 mm long, after whichthey form a somewhat flattened, brownish pupa.In autumn-sown crops, damage is visible as swollen,gouty and short tillers. This can kill the plant or result inother tillers producing weak ears in summer.In spring-sown cereals, if the attack occurs beforestem elongation, the tiller will be stunted, swollen andgouty and never produce an ear. If the plant is moredeveloped, damage will be less severe; a poorlydeveloped ear emerges with immature grains spoiledon one side, resulting in yield being halved.© Jon OakleyGout fly larva in springbarley© ADASAdult gout flyLife cycle1234Larvae overwinter in the centre ofthe plant, close to the root.Larvae pupate.Adult flies emerge and lay eggs onleaves close to the central shoots.Hatching larvae burrow into thecentre of the shoot.Risk factorsCrops emerged by the end of September are atgreatest risk from the autumn generation of flies.Late-sown winter and spring crops are at greatest riskfrom the spring generation. Crops at, or beyond, GS37by mid-May in southern England or late May in theMidlands usually suffer only minor damage. Oats andmaize are not affected.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec124 153 6 75 Larvae pupate.6 Adult flies emerge and lay eggs onleaves close to the central shoots onearly sown winter cereals, weedgrasses and volunteer cereals instubble. Eggs hatch in 7–10 days.7 If conditions are mild, adults mayremain active.MonitoringGout fly is sometimes seen near woodlands andhedgerows.Plants can be checked for the presence of eggs atGS12 in May and June and September/October. Thesecan be seen with the naked eye.ThresholdsLimited evidence suggests that treating winter cropsis economic if eggs are found on more than half ofplants at GS12.Currently, there is no threshold for spring-sown crops.Non-chemical controlSow winter wheat and barley after late September if insheltered fields near woodland. Sowing spring cropsas early as practical in high-risk areas will minimisedamage.Two parasitoid species are known.Insecticide resistanceNone known.Gout fly leaf damage© Jon OakleyGout fly eggs97Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies98

Leatherjackets (Tipula paludosa and Tipula oleracea)ImportanceLeatherjackets are the larvae of crane flies (daddylonglegs). They are soil-inhabiting pests that mainlyfeed on roots and the underground parts of the stem.Risk factorsAttacks frequently occur following a grass rotation.Larvae continue feeding in ploughed down turf,moving on to feed on the new crop when the turf rotsaway. This leads to damage suddenly appearing someweeks after crops emerge.Leatherjackets are usually most numerous afterprolonged damp conditions in late summer and earlyautumn. Dry September weather can reduce numbersconsiderably because eggs and young leatherjacketsare vulnerable to desiccation.Winter cereals, particularly those sown late, may be attacked in autumn and mildwinters (soil temperatures >0.5°C). Seedlings of spring-sown crops are mostvulnerable in April and May, when the leatherjackets are large and voracious.Cereal crops are less likely to suffer economic damage once they have tillered.99Crops affected✔ Cereals✔ OilseedsVegetable brassicasPotatoesCarrotsAlliums✔ Peas✔ Field beans✔ Sugar beetLettuceLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 Adults emerge and lay eggs.2 Eggs hatch.3 Larvae feed when soil >0.5°C.4 Main larval feeding period.5 Larvae pupate near soil surface.6 Pupae.3 5 6 14Pests: Flies, thrips and sawflies2© BBRO3Adult crane flyLeatherjackets (Tipula paludosa and Tipula oleracea)Identification and symptomsThe larvae (leatherjackets) are greyish-black and growto 40 mm. They have a tough skin and are plump andsoft.The adults (crane flies) have a long body (approx.25 mm), ungainly legs and narrow wings. Adultsemerge from August to September.Leatherjackets usually feed just below the soil onroots and stems but on warm, damp nights they mayfeed on the surface, making ragged holes in leavesand cutting off stems like cutworms.MonitoringLeatherjacket numbers can be assessed before ploughing by soil sampling using a10 cm diameter soil corer. A total of 20 cores are taken from an area not exceeding4 ha. The soil is then washed and sieved in a laboratory to extract theleatherjackets. Alternatively, a Blasdale apparatus can be used, which drivesleatherjackets into trays of water by heating the soil cores from above.An alternative method is to drive plastic pipes into the ground and fill them to nearthe brim with brine. Any leatherjackets will float to the surface. Proprietary brinebasedtesting kits are available.If damage is observed in established crops, leatherjacket numbers can beassessed by scratching soil either side of crop rows.ThresholdsSpring cereals: 50 leatherjackets/m 2 , or 5 in 12 pipes, or 5/m of row.Oilseeds: >50 leatherjackets/m 2 , or >5 in 12 pipes, >5/m of row.Non-chemical controlCultivations decrease the populations of this pest. Ploughing in July and earlyAugust (before the main egg-laying period) and ensuring the old sward is wellcovered by soil can largely prevent attacks but could increase the risk of wheat bulbfly in the east of the UK. If ploughing occurs later, thorough consolidation and agood tilth can enable a crop to grow away, minimising the period in which it isvulnerable.The larvae of the main pest species, T. paludosa, stop feeding by mid-June, soestablishing crops, particularly vegetable brassicas, later than this can avoiddamage to seedlings.Insecticide resistanceNone known.© Jon OakleyLeatherjackets (cranefly larvae)Pests: Flies, thrips and sawflies100

Onion fly (Delia antiqua)Onion fly (Delia antiqua)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrots✔ AlliumsPeasField beansSugar beetLettuceImportanceOnion fly is a very localised pest in the UK.Onion seedlings attacked by onion fly larvae quicklycollapse and die. Larger plants are renderedunmarketable by the damage caused by larvalfeeding.Risk factorsUsing implements that damage onion plants canincrease the likelihood of infestation by onion fly.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecIdentification and symptomsThe adult fly is pale grey, hairy and 5–7 mm long. Theegg is elongate (1 mm long) and white in colour. Eggsare laid in batches of up to 30 in soil adjacent to hostplants or in leaf sheaths. Females may lay 100–500eggs during their lifetime. The larva is a white maggotwhich reaches 9–10 mm in length when fully grown.The pupa is oval, reddish-brown to dark brown and6–7 mm long.Onion seedlings attacked by onion fly larvae quicklycollapse and die. When onion fly maggots are presentin large numbers this can lead to patchy crops. Olderplants wilt and then the foliage may discolour and thendry out or start to decompose. Larger bulb onionswithstand attacks but eventually the foliage will die.When bulbs are cut open, larval feeding damage isevident.© University of WarwickOnion fly damage© University of Warwick1 Onion flies overwinter as pupae in the soil.23The first generation of flies emerge in May/Juneand the first eggs are usually laid towards theend of May.Larvae move through the soil and burrow intothe bases of plants, where they feed on softtissue.4 Pupation occurs in the soil near to the host plant.51 412356The second generation of flies emerges inJuly/August.6 Second generation of larvae.© University of WarwickOnion fly life stagesThere are usually two generations per year but, in warm locations, there maybe a partial third generation.MonitoringColoured water or sticky traps can be used to monitoronion fly adults. White, blue and yellow traps havebeen used. There is no validated forecasting systemfor onion fly in the UK.ThresholdsThere are no established thresholds but trap capturesdo indicate when onion flies are active and hownumbers change during the season.Onion fly damageNon-chemical controlOnion fly is a very localised pest in the UK and crop rotation may be an effectiveway of reducing the risk of infestation.Natural controls are likely to include generalist predators, such as certain species ofbeetle, insect-pathogenic fungi and parasitoids (beetles and wasps).Irradiated sterile male onion flies are released annually into some onion cropsgrown in the Netherlands. If they mate with wild female flies, the eggs are sterile.Insecticide resistanceIn North America, onion fly populations have developed resistance to a number ofinsecticides, including the organophosphate chlorpyrifos.101Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies102

Orange wheat blossom midge (Sitodiplosis mosellana)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce103Pests: Flies, thrips and sawfliesImportanceOrange wheat blossom midge larvae feed on thedeveloping seeds, causing small, shriveled grains withpoor germination. Damage to the outer layer of thegrain (pericarp) allows water to enter, resulting insprouting in the ear and facilitating secondary attackby fungi causing fusarium and septoria. This affectsboth the yield and quality of grain harvested.Risk factorsPotentially damaging midge populations may be foundin any field where wheat has been grown over thepast four years. Larvae pupate in warm, moist soil,usually after heavy rainfall. Midges usually fly whenthe air temperature exceeds 15°C. On mild, sunnydays they will fly later in the evening.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec123451 2 3 5Larvae overwinter in a cocoon. They can survive inthe soil inside cocoons for ten years or more. Theypose a major threat for up to four years.Larvae emerge and move to the soil surface. If thesoil is warm (>13°C) and moist, the larvae pupate.If not, they return to the cocoon stage.Adults emerge, resting at the crop base during theday and laying eggs in the florets from dusk.Eggs hatch within 4–10 days and larvae feed on thedeveloping grain. Larvae that hatch after floweringdo not develop properly and cause little damage.Larvae feed on developing grain for about 2 weeks,then drop to the ground and burrow into the soil.4© Jon OakleyAdult orange wheatblossom midgeIdentification and symptomsAdult midges are orange and about 3 mm long. Males have long, featheryantennae. Females have a short ovipositor and lay cylindrical eggs. Larvae areorange and up to 3 mm long.1Orange wheat blossom midge (Sitodiplosis mosellana)MonitoringSusceptible crops should be monitored from the start of ear emergence (GS53–59).Pheromone traps provide the earliest warning of midge activity. Place two traps ineach field where the midge has been at damaging levels in the past two years,even if the current crop is not a cereal. Set traps at crop height at GS45 one weekbefore ear emergence and leave until flowering (GS61).Monitoring for adults laying eggs on ears during earemergence is usually best done from mid-eveningwhen the midges are more evenly spread. Part the cropand count the number of midges.Yellow sticky traps can also be hung at ear height at thestart of ear emergence and the presence of midges inspider webs is also a good indication that the pest is active.ThresholdsPheromone traps30 or more midges: General risk in the next week.Monitor crops for females.More than 120 midges: Very high risk. Treat wheat cropsin surrounding fields at susceptible growth stages(GS53–59) as soon as possible.Visual crop inspectionFor feed crops: 1 midge per 3 earsFor milling and seed crops: 1 midge per 6 earsOrange wheat blossommidge damageSticky trapsA catch of around 10 midges per trap indicates a significant risk.Non-chemical controlGrowing resistant varieties is a very effective way of minimising risk. Refer to theHGCA Recommended List for more information. In more sheltered fields, reducingthe frequency of wheat crops in the rotation can help reduce midge populations.This pest is attacked by a number of generalist predators but the most importantnatural enemies are small parasitic wasps, especially Macroglens penetrans, whichlay their eggs in the midge eggs. The resulting parasitoid larvae develop on themidge larva once it has overwintered, so crop damage is not immediately reduced.Parasitism levels can exceed 80%, however, so a useful level of control can beachieved.Insecticide resistanceNone known.© ADASOrange wheat blossommidge larvae© ADASPests: Flies, thrips and sawflies104

Pea midge (Contarinia pisi ) Pea midge (Contarinia pisi )Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliums✔ PeasField beansSugar beetLettuceLife cycle1 Larvae overwinter in soil in cocoons.23456ImportancePea midge attacks can result in loss of yield, whichcan be very serious where populations have built up inintensive pea-growing areas. Vining peas can be moresusceptible than combining peas and yields may besubstantially reduced.Risk factorsAttacks are generally more severe in areas wherepeas have been grown previously.Larvae pupate. Some may remain in the soil for ayear or more.First generation adults emerge and lay eggs onthe crop. Hatching larvae enter buds to feed.First generation larvae drop into the soil. Somepupate to create second generation while othersremain to overwinter.Second generation adults emerge and lay eggson the crop. Hatching larvae enter buds to feed.Second generation larvae drop into the soil tooverwinter.Crops are most susceptible at the early green budstage. From the Humber northwards, vining peas maynot be attacked until late June, so early crops mayescape serious damage.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 3 54 6© PGROPea midge adult© PGRO1Pea midge larvaeIdentification and symptomsThe adults are gnat-like flies with a yellow-grey bodyabout 2 mm long and six long legs. The head is dark,with a pair of very fine antennae. The semi-transparentwings are slightly longer than the body and are foldedtogether along its back when the midge is at rest.The eggs are approximately 0.3 mm long, oval with atail-like tip and have a translucent, jelly-like appearance.They are laid in batches of 20 or more on therudimentary buds and the leaves surrounding them.Pea midge damageHatching larvae enter the developing buds, where theyfeed at the base of the ovaries. They may also feed in the clustered leaves of theterminal shoot and the pods. After about ten days, larvae reach maturity and dropto the soil. At this stage, they are 2–3 mm long and a dirty white colour.Infested buds become swollen, gouty and do not produce pods, thereby directlyaffecting yield. Larval feeding can also cause the leading shoots to become deformed,limiting their extension growth and producing a "cabbage" or "nettle-head" appearance.Attacked pods become malformed and contain numerous white larvae. In wet periods,damaged tissue may also provide a site for infection by fungi such as Botrytis spp.MonitoringA monitoring system (Oecos Ltd) provides advance warning of adult emergence.The system comprises four sticky traps with pheromone lures. These should beplaced 10 m apart in the previous year’s pea field by the third week of May tomonitor emergence from overwintering sites. Traps should be inspected at leasttwice weekly and the sticky cards replaced each time.ThresholdsIf more than 500 midges are caught on one trap, susceptible pea crops in the nearvicinity should be examined for the pest. This should be done as late in the day aspossible, as the female midges fly into the crop in the afternoon.Non-chemical controlCultural controls include early spring sowing, the selection of early varieties, croprotation and deep ploughing to bury the overwintering larvae. Sowing peas on landadjoining previously infested land should be avoided.A number of parasitoids have been indentified and the bright red larvae of themidge, Lestodiplosis pisi, prey on the pea midge larvae.Insecticide resistanceNone known.© PGRO105Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies106

Saddle gall midge (Haplodiplosis marginata)Saddle gall midge (Haplodiplosis marginata)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceSaddle gall midge is a sporadic pest of cereals, whichusually persists at low population levels. In 2010 and2011, local epidemics were reported in centralEngland, particularly in continuous cropping or tightcereal rotations.Yield loss is caused by the constriction of the vascularsupply to the ears and also by lodging of gallweakenedstems in high winds.Risk factorsLarge populations are associated with heavy soils.Warm and damp soil conditions in May/June are idealfor adults to emerge and lay large quantities of eggswithin a short period.Crops are at most risk when larval feeding coincides with stem extension. Latesownwinter wheat and barley and spring-sown cereal crops are, therefore, atgreatest risk. Winter-sown oats attract adults for egg laying but are rarely seriouslydamaged.Overwintering larvae are able to delay pupation to subsequent years if soilconditions are unsuitable, ie very dry, so pest numbers have previously been ableto build up in continuous cereals.Life cycle1 Larvae overwinter in soil.2 Larvae pupate.345Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 35Adults emerge and lay eggs along the veins ofcereal and grass leaves.Hatching larvae move down the leaf to feed onthe stem underneath the leaf sheath. This feedingcauses a saddle-shaped gall.Mature larvae fall off the plant, into the soil tooverwinter.41© Dewar Crop ProtectionAdult saddle gallmidgeIdentification and symptomsAdult midges are red and up to 5 mm long. Blood-redeggs are laid in a chain or raft-like pattern along leafveins on either side of leaves. Hatching whitish-greenlarvae make their way down to the protection of theleaf sheath to feed on the surface of the stem. Bymaturity in mid-July, the larvae have developed into anorange-red colour.Larval feeding causes the formation of characteristicsaddle-shaped galls. They usually occur on the topthree internodes. The stem can be completelydestroyed if numerous galls fuse together. Galls areoften hidden beneath the leaf sheath. Symptoms maybe more apparent as uneven contours on the stemsurface.Larval feeding also restricts nutrient supply to the earand can result in white heads.MonitoringYellow water traps are effective at catching adultmidges and yellow sticky traps may also be used.Midge development in soil can be monitored by takingregular soil samples and extracting the developmentalstages by wet sieving.ThresholdsNone known.Non-chemical controlNon-cereal break crops in the rotation will allowpopulation levels to decline. The use of oats, which actas a trap crop may also reduce the risk. Early sowingin September can also reduce the risk of damage.Carabid beetles, staphylinid beetles and spiders maygive some control by preying on larvae in the soil.Some evidence of control by parasitoids has beenrecorded in Germany.Insecticide resistanceNone known.© Dewar Crop ProtectionSaddle-shaped galls onwheat under the leafsheath© Dewar Crop ProtectionSaddle gall midgelarvae© ADASSaddle gall midgeeggs107Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies108

Swede midge (Contarinia nasturtii)Swede midge (Contarinia nasturtii)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceThe larva of the swede midge attacks many types ofbrassica crop and leads to loss of yield and quality. Itis a sporadic pest in the UK. There is a suggestion thatoutbreaks may occur in years of high humidity andtemperature.Risk factorsWith multiple generations and a high reproductivepotential, swede midge populations can build up veryquickly under continuous production of a host crop.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecIdentification and symptomsThe adult is a tiny, greenish-yellow to light brown fly(1.5–2 mm), which is difficult to distinguish from otherclosely-related midge species. It has very hairy wings.The egg is very small (0.3 mm), transparent and thenturns creamy white as it develops.The larva is a small maggot, initially 0.3 mm in size andreaching a final size of 3–4 mm. Larvae are initiallytranslucent, becoming increasingly yellow until lemonyellowat maturity. The swede midge pupates in thesoil.Damage symptoms include swollen flowers, scarringin the growing point and on leaf petioles and flowerstalks, blindness and crinkled leaves. It often kills themain shoot, in which case the side shoots grow outcausing a many-necked plant.© Stina Andersson – HIR MalmöhusDamage due to swedemidge larvaeThere are usually three generations in a year. Duringperiods of drought, the larvae may enter a period ofdormancy but development resumes after rainfall.1231The larvae of the third generation overwinter inthe soil.These larvae pupate in the spring and adultsemerge.Each female lays 60–120 eggs in batches of 15–20on the younger parts of the plant, particularly theterminal bud. The larvae feed mostly on thegrowing point but can live on almost any part ofthe plant within an almost liquid environment.When fully grown, the larvae move to theground, form cocoons in the soil and pupate. Thepupa works itself out of the cocoon and moves tothe soil surface until the front end protrudes andthen the adult emerges.231© Stina Andersson – HIR MalmöhusAdult swede midge onsticky trapMonitoringPheromone traps are available; however, knowledge of insect identification and amicroscope are required to separate the male swede midges from other species offly that accidentally enter the traps.ThresholdsNone known.Non-chemical controlAnnual crop rotation is the single most effective way to reduce swede midgepopulations in the field.Crop covers might exclude swede midge, provided the mesh size is sufficientlysmall.Insecticide resistanceThere is no evidence of insecticide resistance in UK populations. It is believed thatthere is a risk of resistance developing in Canada, where it is becoming a seriouspest.109Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies110

ThripsCrops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrots✔ Alliums✔ Peas✔ Field beans✔ Sugar beetLettuceImportanceField thrips (Thrips angusticeps) attack pea and beancrops at early emergence, feeding inside the tightlyrolled leaves of the growing point, and continue tofeed throughout the growing season. They alsodamage sugar beet foliage.Pea thrips (Kakothrips pisivorus) attack pea cropsduring and after flowering, causing damage to thepods.Onion thrips (Thrips tabaci) are a pest of several cropsin the UK, particularly leek, salad onion, storedcabbage and sugar beet. Plants with obvious thripsfeeding damage are considered unacceptable for salein many cases and, therefore, the economic impact ofa thrips infestation can be severe.In addition to field thrips and onion thrips, sugar beet leaves are also damaged byCaliothrips fasciatus.Life cycle – Field thrips123Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2Field thrips overwinter in soil as short-wingedflightless adults.Field thrips emerge from soil to feed on youngcrops.Adult field thrips with normal-sized wings migrateto other crops.31© Rothamsted Research LtdThripsLife cycle – Pea thripsJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12 51341 Nymphs overwinter in soil.2 Nymphs pupate.3Winged adults emerge and move into crops. Eggs are laid in flowers and onpods. Hatching nymphs feed on the crop.4 Populations peak mid-June.5 Nymphs descend into soil.Life cycle – Onion thrips123Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1In the UK, onion thrips overwinters in the adult stage. Overwintered hostvegetable crops such as leek are preferred overwintering sites but they willoverwinter in other locations, such as overwintered cereal crops.Once temperatures rise in the spring, female thrips start to lay eggs, eitherafter dispersing to new hosts or on the overwintering host if this is still asuitable food source.Following egg hatch, there are two active larval stages and two inactivestages (pre-pupa and pupa).A generation (egg to adult) takes about 52 days at 12.5°C and 15 days at 25°C.231Thrips111Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies112

ThripsThrips© PGROField thrips© PGROField thrips damageRisk factorsField thrips and pea thripsAttacks are most severe during periods of slowgrowth, in cold, dry springs, and in particular on stonysoils. In good conditions, the crop will usually toleratedamage and grow away.Onion thripsOnion thrips populations thrive in warm and dryconditions, which not only promote fast larvaldevelopment but are ideal for flight. The crypticbehaviour of onion thrips means that they are a verydifficult target for insecticides that work by contactaction. This may be particularly true for the larvae,which do not move onto the higher and moreexposed parts of the plant.During the winter of 2006/07, there were a number ofreports of onion thrips damage to stored cabbage. Thewinter was exceptionally warm and it is likely that thisfavoured the continued development of thrips insidecabbage maintained in ambient stores.Identification and symptomsField thrips and pea thripsThe adult thrips are narrow-bodied, dark and shiny, andable to reach approximately 2 mm in length. Adultshave two pairs of wings, usually folded along theback, which they can use to migrate large distances.The two species are indistinguishable withoutmicroscopic examination.Minute, kidney-shaped eggs are embedded into thetissues of flowers and pods. The immature stages aresimilar in shape to the adults but have no wings andare bright yellow with a conspicuous black tip at therear end.Field thrips causes damage to the surface of leaves,resulting in mottled patches and distortions. It may bepossible to find these thrips by carefully unfolding theleaflets of affected seedlings. On beans, the leaves mayappear shiny and speckled with sooty black markings.The undersides of bean leaves develop a rusty browndiscolouration. On peas, field thrips cause the foliage tothicken and pucker, with a translucent spottingdeveloping on the surface of leaves. Pea thrips attacklater in the season and cause silvery blemishes on thesurfaces of pea pods.In many situations, peas and beans can outgrow theinitial attack, with no long term effects on the crop.However, occasionally, when the attack is severe, peasmay produce blind shoots that form no flowers, developmultiple secondary shoots and develop as small bushyplants. This is called ‘Pea Dwarfing Syndrome’ and plantswill not recover fully. Bean leaves may die off completelyand severely arrest the growth for a week or two.Onion thripsThe adult thrips are usually brown in colour and havetwo pairs of wings fringed with long hairs. They areapproximately 1 mm in length. The eggs are minute(0.3 mm long), kidney-shaped and white/yellow in colour.Larvae are yellow/cream in colour, starting around0.5 mm in length and feeding until they have reachedthe size of the eventual adult.Feeding by adult and larval thrips damages the hostplant via direct removal of cell contents. As individualplant cells are killed, scarring of the leaf in the form ofsilvering is observed. On cabbage, feeding by thrips canresult in small, brownish-grey growths on the leafsurface as well as silver-coloured lesions.Sugar beetOn sugar beet, thrips feed mainly on young leaves,causing superficial silvering, puckering or reddening.Attacks on heart leaves that are still curled can preventnormal growth and leaf expansion. Damage to thehypocotyl near the soil surface is hard to prevent andcan cause seedling death.© Joshua BurnstoneOnion thrips larva© University of WarwickOnion thrips damage© Rothamsted Research LtdThrips damage insugar beet113Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies114

ThripsMonitoringField thrips and pea thripsFrequent examinations of the emerging crop should be made. In peas, this shouldbe from the first appearance of pods until the pods are full. Examining lateemergingbean crops is often unnecessary, as they usually escape damage.Onion thripsAdult onion thrips can be monitored using sticky traps. Blue and white areconsidered to be the preferred colours. It may be sufficient to trap thrips at one ortwo locations within a region, as the pattern of activity appears to be consistent inany year. Thrips infestations can also be monitored directly by examining the cropand it is probably easier to assess damage than to count thrips on plants. The bestapproach may be to assess the youngest leaves on allium crops: this will indicatethe current level of damage rather than old damage.ThresholdsField thrips and pea thripsTreatment in peas and beans is justified as soon as damage is seen. In beans, as mostdamage occurs while the crop is young, treatment after mid-May is not worthwhile.Onion thripsIn many cases, adult thrips have been captured on sticky traps before thrips werefound on allium plants, indicating that traps could be used to provide an early warningof colonisation. However, there seems to be little opportunity to use the actualnumbers of thrips captured on traps to predict the severity of infestation on plants.ThripsIrrigation to reduce thrips populations is employed by growers in many countriesand there appears to be a consensus that this is effective.There has been some success in controlling thrips species with predators,although this is mainly in protected crop environments and using augmentative orinundative techniques. This technique has not been evaluated outdoors in the UK.Entomopathogenic nematodes were investigated as a potential biological controlagent on leek in a Defra project. The nematodes appeared to survive for severaldays in water droplets at the base of the leaves of leek plants but did not do so onthe foliage and there was no evidence that they reduced thrips numbers. It is notknown whether nematodes trapped in the droplets are able to parasitise nearbythrips and there is the potential for further work in this area to determine whetherthey are effective either against the larval stages on the foliage or the pre-pupal andpupal stages in the soil. Identification of the susceptible stage would influence theapplication strategy that might be used.Insecticide resistanceInsecticide resistance to pyrethroid insecticides in field populations of onion thripsin the UK was confirmed in 2006. There is no evidence of resistance in the otherspecies.Non-chemical controlThrips are predated by spiders, ladybirds, predatory flies and lacewings.Field thrips and pea thripsFor field thrips and pea thrips in high-risk areas, sow late-emerging crops.Onion thripsVarietal resistance to onion thrips exists in some cultivars of onion and, in the USA,use of some resistant onion varieties was more effective in control of onion thripspopulations than application of insecticides. There has been no comprehensivesurvey of resistance in cultivars grown in the UK.Intercropping has been investigated as a method of thrips control in onion cropsand was found to reduce infestations by 50% or more. Similarly, undersowing withclover has shown excellent potential for the reduction of thrips populations in leek.With both approaches, competition between the crop and companion plants maylimit their usefulness, together with the additional costs of taking such anapproach.115Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies116

Turnip sawfly (Athalia rosae)Turnip sawfly (Athalia rosae)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoes© ADASCarrotsAlliumsPeasField beansSugar beetLettuceAdult turnip sawflyLife cycleImportanceThe turnip sawfly was considered a serious pest ofbrassicas in the 18 th and 19 th centuries but wasthought to have been eradicated early in the 20 thcentury. However, since the 1940s, sporadic, minoroutbreaks have been have been reported and, in2006, a major outbreak caused significant cropdamage in southern England. The larvae are generaland potentially severe feeders on the leaves ofbrassica plants.Risk factorsWarm conditions increase adult activity, as they onlyfly at temperatures above 18°C. Favourable windsincrease the possibility of mass immigrations frommainland Europe, where the pest is more common,meaning that southern counties are at greater risk.A third generation can occur after hot summers andthe arrival of the adults in oilseed rape then coincideswith the early stages of crop emergence.The ability of a crop to compensate for turnip sawflylarval attack is largely dependent on how quickly it isable to establish and grow away. Where cropsemerge slowly, there is a greater risk of significantdefoliation by virtue of the low green leaf area indices.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 25 73641 Pupae overwinter in soil.2 First generation of adults emerge and lay up to 300 eggs in the margin of host leaves.3 Eggs hatch in 6–8 days and larvae feed inside and then externally on theunderside of the leaf.4 At maturity, the larvae drop to the soil to pupate.5 Second generation of adults emerge and lay eggs.6 Third generation of adults emerge and lay eggs.7 Pupae overwinter in soil.Identification and symptomsThe adults are orange and black in colour, around7-8 mm in length. The abdomen is entirely orange,while the thorax is orange with two black ‘shoulderpads’ (other similar sawflies have an entirely blackupper surface to the thorax). Legs are orange withblack bands.The caterpillar-like larvae are greenish-black in colourwith a paler stripe along the side of the body, have ashiny black head and can grow to 18 mm long. Thelarvae feed gregariously on leaves, which can bequickly skeletonised.MonitoringAdult sawflies feed on pollen and nectar, so theirpresence in flowering hedgerows can give an earlywarning of imminent attack. Yellow sticky traps andwater traps can also be used to monitor the presenceof adults. Monitoring should begin in May andcontinue until September. The purpose of monitoringshould be to detect sudden increases in adult activity,which might indicate that a mass immigration hasoccurred. Turnip sawfly larvae should be easily visibleon damaged leaves or close to damaged plants.ThresholdsOilseed rape: 1–2 larvae/plant.Please note that this is a German threshold and littleinformation is available on its validity under UKconditions; it is, therefore, offered for guidance only.Non-chemical controlSpring-sown crops should be situated away fromknown overwintering sites (such as autumn-sownoilseed rape), wherever possible.High value, sensitive crops can be protected fromadults using covers, such as insect-proof mesh.Turnip sawflies are hosts for parasitic wasps and flies.Insecticide resistanceNone known.© Jon OakleyTurnip sawfly larvae© Dewar Crop ProtectionTurnip sawfly larva© University of WarwickTurnip sawfly larvaeand damage117Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies118

Wheat bulb fly (Delia coarctata)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceWheat bulb fly adult123456© ADASLarvae hatch and invade roots of wheat, barleyand rye.Larvae attack 3–5 further shoots.Larvae pupate at base of plants.Adult flies emerge and feed on saprophytic fungion host plant.Eggs laid on bare soil and between row crops.Overwinter as eggs.ImportanceWheat bulb fly is one of the most serious pests ofwheat in the UK, although it is not abundant everyyear.Yield loss depends on tiller density at the time ofattack. Crops at the single shoot stage in February aremost vulnerable and may be totally destroyed. Up to100 larvae/m 2 can be tolerated by a well-tillered cropwithout an economic impact on yield.Risk factorsAll cereals except oats are attacked, with autumn- orwinter-sown crops being most susceptible. Springwheat and barley are at risk if sown before March butexperience little or no damage if sown later.Eggs are laid on bare soil following fallows, set-asideor early harvested crops, such as vining peas, wherecultivation occurs between mid-July and mid-August.Adults will also lay eggs between row crops, such aspotatoes, sugar beet, celery and onions, under hot,dry conditions, especially if the foliage is wilting.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 3425© ADAS6Wheat bulb fly larvaWheat bulb fly (Delia coarctata)Identification and symptomsAdults are slightly smaller than, but similar inappearance to, house flies.Hatching larvae are legless, white, without a distincthead and are pointed at the front end and blunt at thehind end. Once a host has been found, the larvaebore into the plant at the base of the stem to feed.Between mid-April and early May, larvae leave theplant to pupate in the soil.Damage is seen as classic 'deadheart' symptoms. These symptoms may bedifficult to detect without careful examination until February or March.MonitoringEgg numbers can be estimated from soil samples. An HGCA-funded survey isdone by ADAS to aid decision-making on chemical control. Seewww.hgca.com/pests to see which regions and rotations have reached thresholdlevels. The timing of egg hatch can also be determined by soil sampling.When deadhearts are found, plant samples can be examined to determine thenumber of larvae present.Thresholds– Fewer than 100 eggs/m 2 : Seed treatment justified in spring-sown cereals– 100–249 eggs/m 2 : Seed treatment justified in late-sown and spring-sown cereals– 250–500 eggs/m 2 : Seed treatment justified in late-sown and spring-sown cereals;egg-hatch spray may be justified– More than 500 eggs/m 2 : Egg-hatch spray justified in early sown cereals; seedtreatment and egg-hatch spray justified in late-sown and spring-sown cerealsNon-chemical controlGround beetles and their larvae are the main predators of wheat bulb fly eggs.Wheat bulb fly larvae may be parasitised by small rove beetles, particularlyAleochara bipustulata, with up to 50% killed.The numbers of eggs laid can be reduced by opting not to cultivate from late Julyto early August. On bare fallows, a crop of mustard sown to cover the soil by mid-July will also reduce egg laying. The impact of the pest can be reduced by sowingearly with an increased seed rate, as the crop will have started to tiller before eggshatch and be able to tolerate attack.Insecticide resistanceNone known.© Dewar Crop ProtectionDeadheart symptoms119Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies120

Yellow cereal fly (Opomyza florum)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce1 Eggs overwinter.2 Eggs hatch.3 Larvae enter and feed on wheat shoots.4 Larvae pupate in the shoot or soil.5 Adult flies hatch.6 Adults spend the summer in woodland.7 Flies move to early sown wheat crops.8 Eggs are laid at the base of plants.ImportanceEach yellow cereal fly larva damages only a singleshoot, so economic impact is generally low. Mostcrops can withstand a considerable number of larvaeby producing compensating tillers.Risk factorsCrops at greatest risk are those with low plantpopulations and early sown crops in sheltered fieldsclose to woodland.Life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 4 5 712683© ADASYellow cereal fly adultYellow cereal fly (Opomyza florum)Identification and symptomsThe adult fly is small (5–5.5 mm long) with an orangebrownbody and black wing markings. Females layeggs on soil near host plants.Upon hatching, the larvae crawl up host plants, makingtheir way under the ensheathing leaves to the growingpoint. The larvae enter the shoot by making an incisionin the side or just above the first node. This can beseen as a clean, brown line encircling or spirallingaround the shoot (in contrast to the ragged hole left bywheat bulb fly). The larvae are yellow with pointedends and are thinner than wheat bulb fly larvae butsimilar to frit fly larvae (though occurring later in thewinter). At maturity, the larvae either pupate in theshoot or leave to do so in the soil, forming a hardbrown puparium.Larval feeding results in classic ‘deadheart’ damage,where the central shoot becomes yellow and dies.Symptoms are similar to frit fly damage (see page 95),particularly in winter wheat, but are not noticeable untilspring, long after frit fly attack has ceased.MonitoringIt is possible to dissect plants to determine the level ofpest infestation but the economic impact of yellowcereal fly is generally low, as it only infests a single tiller.ThresholdsNone known.© ADASYellow cereal fly larva© ADASEntrance holeNon-chemical controlGround beetles feed on soil-borne eggs and pupae. Ladybirds and soldier beetlesfeed on pupae.It should be possible to avoid economic damage by planting at least 200 plants/m 2in vulnerable situations.Insecticide resistanceNone known.121Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies122

Minor/emerging pestsAllium leaf miner (Phytomyza gymnostoma)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrots✔ AlliumsPeasField beansSugar beetLettuce© Tom Will, VCS (UK) LtdAllium leaf minerdamage© University of WarwickAllium leaf minerdamageThe allium leaf miner was first detected in the UK in2002, since when it has spread, particularly in theMidlands. While this species was initially a pest ofallotments and gardens, it has now been founddamaging commercial crops of onion, leek and garlic.Relatively little is known about the biology of this newpest. It is likely that it has two generations per year inthe UK: the first generation laying eggs in March/Apriland the second generation laying eggs inOctober/November.Before laying eggs on the stems or bases of leaves,the female flies feed by making punctures in theleaves and sucking up the exuding sap. This causesdistinctive lines of white dots on the foliage. Thelarvae make tunnels in the foliage, stems and bulbs.Pupation takes place mainly within the stems andbulbs but some pupae may end up in the soil,especially where plants have rotted off.Plants affected by allium leaf miner tend to rot due tosecondary infections from fungi and bacteria thatdevelop in the damaged tissues.Plants could be protected by covering them withinsect-proof netting at times when the adult flies areactive and laying eggs.Minor/emerging pestsCereal stem sawfly (Cephus pygmaeus) and leaf sawfliesCrops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceCrops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceThe cereal stem sawfly (Cephus pygmaeus) is seldomof importance; however, crop losses can occur insome years when there are large numbers of thepest. Winter wheat is usually attacked but damagecan sometimes be seen© Jon Oakleyin spring wheat andbarley.A number of species ofleaf sawfly also attackcereals, causing damagein early summer;however, this is rarelyeconomically important.There are severalparasitoid species thatattack cereal sawflies.Yellow wheat blossom midge (Contarinia tritici )Cereal stem sawflyadultYellow wheat blossom midge is less common thanorange wheat blossom midge and is rarely damaging.It follows a similar life cycle but is less persistent, withlarvae pupating within three years of entering the soil.Adults emerge at a similar time to orange wheatblossom midge but lay eggs slightly earlier (as theboot splits to reveal the ear).The larvae feed on thestigma, preventingpollination anddevelopment of the grain,and then on the anthers,which are retained withinthe floret. After two tothree weeks of feeding,they jump from the floretin wet weather. Somelarvae pupate inSeptember, forming apartial second generationthat feeds on couch grass.© Jon OakleyYellow wheat blossommidge adult123Pests: Flies, thrips and sawfliesPests: Flies, thrips and sawflies124

Further informationAlerts and bulletinsHDC Pest Bulletin: Sponsored by Syngenta and hosted on the Syngenta website,this bulletin aims to provide growers with topical and valuable agronomyinformation throughout the growing season.www3.syngenta.com/country/uk/en/AgronomyTools/HDCPestBulletinHDC PublicationsAvailable at www.hdc.org.ukHDC Factsheet 03/13: Bean seed fly (2013)HDC Factsheet 35/12: Minor pests of Brassicas (2012)HDC Factsheet 10/11: Leafminers of cruciferous salad crops (2011)HDC Factsheet 09/11: Control of thrips in Allium and Brassica crops (2011)HDC Factsheet 11/10: Turnip sawfly: biology and control (2010)HDC Factsheet 28/05: Swede midge control in brassica crops (2005)HGCA PublicationsAvailable at www.hgca.com/publicationsHGCA Information Sheet 15: Biology and control of saddle gall midge (2012)HGCA Topic Sheet 118: Wheat bulb fly: risk assessment and control (2012)HGCA G45: Orange wheat blossom midge – guidelines for assessment andcontrol (2009)HGCA Research Review 77: Implications of the restriction on the neonicotinoids:imidacloprid, clothianidin and thiamethoxam on crop protection in oilseeds andcereals in the UK (2013)125Pests: Flies, thrips and sawflies

Pests:Moths andbutterflies

Contents – Pests: Moths and butterfliesSpeciesPageCabbage moth (Mamestra brassicae) 127Cutworms (Noctuid moths) 129Diamond-back moth (Plutella xylostella) 131Garden pebble moth (Evergestis forficalis) 133Ghost moth (Hepialus humuli ) andSwift moth (Korscheltellus (Hepialus) lupulinus) 135Large white butterfly (Pieris brassicae) 137Leek moth (Acrolepiopsis assectella) 139Pea moth (Cydia nigricana) 141Silver Y moth (Autographa gamma) 143Small white butterfly (Pieris rapae) 145Minor/emerging pests 147Flax tortrix moth (Cnephasia asseclana) 147Further information 149

Moths and butterflies (Lepidoptera)Butterflies and moths can be important pollinators but their larvae (caterpillars) aresometimes pests.Life cycleMale and female moths usually find each other by scent. This means that pheromonetraps can be used to monitor them. For butterflies, the initial attraction is by sight.The outer skin of thelarva (caterpillar)cannot grow and so Pupamust be shed in aseries of moults as itgrows. When thelarva is fully grown, itturns into a pupa orchrysalis. This is anon-feeding stage,inside which the larvalbody is broken downand reassembled in the adult form.LarvaAdultEggsDefining featuresButterflies and moths aredistinguished from other insectsprimarily by the presence of scaleson the external parts of the body,particularly the wings.AntennaeHindwingForewingThe larvae, caterpillars, have atoughened head capsule and a softsegmented body with three pairsof true legs and up to five pairs ofabdominal prolegs.See page 80 for a comparison ofsawfly larvae and butterfly/mothcaterpillars.HeadProboscisLegsThoraxHeadThoraxAbdomenAbdomenSpiracle (openingof the respiratorysystem)True legsAbdominal prolegsPests: Moths and butterflies126

Cabbage moth (Mamestra brassicae)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceFeeding by the larvae of the cabbage moth can rapidlyskeletonise the outer leaves of large plants andsometimes destroy small plants. Large larvae mayalso bore into the hearts of plants such as headingcabbage. Frass (droppings) and the larvae cancontaminate fresh produce.Risk factorsWhile vegetable brassicas are the most susceptiblecrops, larvae will feed on a wide range of plantspecies, including potato and other vegetables(though without causing economic damage).Eggs may not be detected until damage has occurred.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12 43 51Cabbage moth (Mamestra brassicae)Identification and symptomsAdults are greyish-brown mottled with dark brown andthe forewings have a span of 35–50 mm. There is akidney-shaped marking with a white outline on eachforewing and an irregular white transverse line nearthe wing margin.Eggs are hemispherical (0.5–0.6 mm diameter) andwhite in colour, darkening close to hatching. They arelaid in batches of up to 50.© Peter ThompsonNewly hatched larvae are green and feed gregariouslyon leaves. As the larvae grow, their colouringAdult cabbage mothbecomes more variable and they may be green,brown or even almost totally black. Older larvae have a dusky dorsal stripe,speckled with white and a yellowish, light green or dusky brown stripe low downon the sides. The larvae are 40–50 mm long when fully grown and the larvapupates in a cocoon in the soil.MonitoringMale moths can be captured by pheromone traps. This information can be used totime crop walking to determine whether treatment is required.12345Cabbage moth generally overwinters as a pupa inthe soil, although it may also overwinter as alarva.Adult moths (1 st generation) emerge from pupaeand lay eggs.Larvae feed/pupae formed.Adult moths (2 nd generation) emerge from pupaeand lay eggs.Larvae feed/pupae formed.The second generation isthe most damaging tobrassica crops. Large larvaemay be found on cropsquite late in the season.© University of Warwick© University of WarwickCabbage moth eggs© University of WarwickThresholdsNone established.Non-chemical controlThis pest is attacked by a number of polyphagous predators. The eggs or larvaemay also be parasitised by certain species of wasp or fly, which eventually kill thelarva. The larvae continue to feed for some time after they are parasitised and socrop damage is not reduced immediately. Larvae may also be killed by viruses.Biological control with egg parasitoids (Trichogramma spp.) has been investigatedoverseas but not in the UK. Pesticides based on certain microbial control agents(fungi, nematodes, viruses) may be effective; however, care should be taken whenchoosing biopesticides based on Bacillus thuringiensis (Bt), as some strains arerelatively ineffective against this pest.There is no host resistance available in commercial cultivars at present. Sources ofresistance in brassicas have been identified in the past.Insecticide resistanceNone known.Cabbage moth larvaCabbage moth larvae127Pests: Moths and butterfliesPests: Moths and butterflies128

Cutworms (Noctuid moths, eg Agrotis segetum)Cutworms (Noctuid moths, eg Agrotis segetum)Crops affectedCerealsOilseeds✔ Vegetable brassicas✔ Potatoes✔ Carrots✔ Alliums✔ PeasField beans✔ Sugar beet✔ LettuceLife cycleImportanceCutworms are the larvae of certain Noctuid moths, inparticular the turnip moth. Older larvae feed underground,damaging plant roots and stems, sometimesso badly that the plant stem is severed. Althoughcutworms are sporadic pests, damage can be severe,leading to the loss of plants and reductions in quality.Young lettuce and leek plants are easily bitten throughby cutworms. Roots and onion bulbs can be renderedunmarketable by cutworm feeding.Risk factorsThe most vulnerable crops are lettuce, leeks and redbeet. Moderately susceptible crops include brassicas,carrot, celery, parsnip and sugar beet.The leastsusceptible crops are onion, potato, swede and turnip.Cutworm damage is most severe in light, sandy soils.The risk of damage is increased in hot, dry years.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec51 423 51 Adult turnip moths lay eggs on plants or on pieces© Tony Morrisof litter and debris in the soil.2 Eggs hatch in around 8–24 days, depending ontemperature and the young larvae seek out and feedon the aerial parts of plants.3 In a further 10–20 days, again depending ontemperature, the larvae go through their secondmoult, becoming ‘third instar’ caterpillars. It is atthis point that they adopt the cutworm habit,Adult turnip mothbecoming subterranean and feeding on roots.4 A second generation of turnip moths may emerge in late summer but thecaterpillars of this generation do not appear to be damaging.5 The pest overwinters as the larvae of the second generation, with pupae formingin April-May.The life cycles of other species may vary from this pattern. For example, Euxoanigricans (garden dart moth) lays eggs in the late summer, which hatch in the followingspring. The larvae feed on beet seedlings during April and May before pupating.Identification and symptomsAdult turnip moths have a wingspan of about 40 mm.The forewings are pale greyish-brown with darkbrown markings which include rings and lines.The eggs are globular, about 5 mm in diameter andwhite in colour, later turning cream with reddishyellowmarkings and an orange band.Fully grown caterpillars are greyish-brown and about40 mm long.Seedlings and young plants are severed from theirroots and die. Cutworms make cavities in stems,rhizomes, tubers and roots of large plants, similar toslugs. Cutworms may move along the rows of cropssuch as lettuce or leek, cutting plants off one afteranother. Damage to root crops may not be evidentuntil harvest.The potato stem borer attacks sugar beet, potatoesand other crops. In sugar beet, it tunnels inside thecrown and upper part of the root of young plants: theroots blacken internally and, externally, there may beblackening on the crown of the root.MonitoringMale moths can be captured by pheromone traps.The ‘cutworm model’ is a computer programme that uses weather data (airtemperature and rainfall) to predict the rate of development of turnip moth eggsand caterpillars. It then predicts the level of rain-induced mortality among the earlyinstar caterpillars and target dates at which to apply irrigation or insecticides.ThresholdsNone established.Non-chemical controlYoung larvae are very susceptible to irrigation while feeding above ground on plantfoliage and well-timed irrigation can be a very effective method of control. To date,biological control with predators or parasitoids has not been investigated in the UK.Pesticides based on microbial control agents (eg Bt) may be effective.Insecticide resistanceNone known.© University of WarwickCutworms© Rothamsted Research LtdCutworm damage tosugar beet129Pests: Moths and butterfliesPests: Moths and butterflies130

Diamond-back moth (Plutella xylostella)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© University of WarwickDiamond-back mothadultLife cycleImportanceDiamond-back moth may infest crops throughout theUK and the larvae can cause damage to the foliage ofcabbage, cauliflower, broccoli, Brussels sprout, kale,Chinese cabbage, swede, turnip, oilseed rape andradish. Large infestations can cause damage to up to100% of plants but yield losses will depend on theimpact of damage on plant growth and quality. Goodcontrol is particularly important where the marketablepart of the plant is damaged (cabbage, cauliflower,broccoli, Brussels sprout). Plants with low levels ofdamage usually survive but this may affect uniformitywithin the crop.Risk factorsInfestations are sporadic, so control may not benecessary in every crop in every year.Weather that favours migration from continentalEurope increases the risk of infestation, as thediamond-back moth does not overwinter in the UK inlarge numbers at present. The moths are relativelypoor flyers but may be transported long distances bythe wind.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12 1Relative risk of egg laying and damage: 1 Low. 2 High.The rate of development of diamond-back moth is dependent on temperature, somore generations will be completed in warm locations. In the UK, depending onwhen moths arrive, there may be two to three generations per year. Eggs mayhatch within 2–3 days of being laid and a complete generation takes about 5weeks at 15°C.Identification and symptomsAdult moths are about 6 mm long. They are brownish and have three light brown towhite triangular marks on the trailing edge of each forewing. When the adults areat rest, the triangular marks on the forewings meet to form diamond shapes.Diamond-back moth (Plutella xylostella)The eggs are yellow and laid singly or in small groups,mainly alongside the mid-rib or leaf veins.The larva is light green and has a tapering body that iswidest in the middle. Larvae that are disturbedwriggle violently. Fully grown larvae (15 mm) constructa flimsy cocoon on the leaf surface before developinginto a pupa about 9 mm long.The larvae destroy the foliage of most types ofbrassica crop. They generally eat almost all leafmaterial except the upper epidermis, which makes theleaves appear as if they are covered by lots ofwindows. Large infestations will destroy the leavesentirely. They will damage plants of any age.MonitoringMale moths can be captured by pheromone traps.This information can be used to time crop walking todetermine whether treatment is required.ThresholdsThere are no current validated thresholds for diamondbackmoth in the UK, although thresholds have beendeveloped in the USA and elsewhere. Such thresholdswould need to be dependent on plant type and size.Non-chemical controlFine mesh netting (crop covers) has been tested as amethod of preventing egg laying by female moths buteggs were laid on the mesh and the larvae crawled© University of WarwickDiamond-back mothlarvae on cauliflowerleaf© University of WarwickDiamond-back mothlarval feeding damagethrough onto the crop. Other physical and cultural approaches (companion planting,trap crops) have been investigated but are not as effective as the use of currentlyavailable insecticides.To date, biological control with predators or parasitoids has not been investigated inthe UK. Pesticides based on microbial control agents (Bt and viruses) can be effective.Insecticide resistanceThe diamond-back moth is an important pest worldwide, particularly in tropicalregions. Over the years, populations in these areas have developed resistance toalmost all of the insecticide groups to which they have been exposed repeatedly.There is no evidence at present that the moths migrating into the UK each year arehighly resistant to the actives approved in the UK for diamond-back moth control.131Pests: Moths and butterfliesPests: Moths and butterflies132

Garden pebble moth (Evergestis forficalis)Garden pebble moth (Evergestis forficalis)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceFeeding by the larvae of the garden pebble moth cancause damage to plant foliage. Larvae sometimesmine into the hearts. Frass (droppings), larvae and silkwebbing can contaminate fresh produce.Garden pebble moth tends to be a localised pest.Risk factorsThe larvae hide themselves within plant foliage andinfestations may not be detected until damage hasoccurred.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 2 4 11 Pupae overwinter in the soil.2 Adults (1 st generation) emerge and lay eggs.3 Larvae feed/pupae formed.4 Adults (2 nd generation) emerge and lay eggs.The second generation is the most damaging tobrassica crops.3© Jamie McMillanAdult garden pebblemothIdentification and symptomsAdults have a wingspan of 25–30 mm. The forewingsare yellowish-white, with brown veins, and coveredwith a series of oblique brown lines and shaded areas.Eggs are laid in batches of about 20 on the undersidesof leaves. They are shiny, oval and flattened and areinitially translucent before becoming yellow.Young larvae are yellowish-green but later becomeglossy pale green with yellowish mid-dorsal and lateralstripes. A fully grown larva is 18–20 mm long with arow of black spots along each side. Larvae feed onthe underside of leaves, frequently as a group withinleaf folds and beneath protective silk webbing. Thelarvae pupate in cocoons in the soil.MonitoringMale moths can be captured by pheromone traps.This information can be used to time crop walking todetermine whether treatment is required.ThresholdsNone established.Non-chemical controlThis pest is attacked by a number of polyphagouspredators. The eggs or larvae may also be parasitisedby certain species of wasp or fly, which eventually killthe larvae. The larvae continue to feed for some timeafter they are parasitised and so crop damage is notreduced immediately.To date, biological control with predators or parasitoidshas not been investigated in the UK. It is not clearhow susceptible the larvae are to products based onBacillus thuringiensis (Bt).Insecticide resistanceNone known.© University of WarwickYoung garden pebblemoth larva© University of WarwickGarden pebble mothlarva© University of WarwickGarden pebble mothdamage133Pests: Moths and butterfliesPests: Moths and butterflies134

Ghost moth (Hepialus humuli ) andSwift moth (Korscheltellus (Hepialus) lupulinus)Ghost moth (Hepialus humuli ) andSwift moth (Korscheltellus (Hepialus) lupulinus)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoes✔ CarrotsAlliumsPeasField beansSugar beet✔ LettuceImportanceThe larvae cut off plants just below ground level ortunnel into roots or stems.They are minor and localised pests.Risk factorsThe ghost moth, or ghost swift moth, is common ingrassland, so any crop following a grass ley is liable toattack.Lettuce is especially liable to damage from the swiftmoth, or garden swift moth.© Peter Thompson © Peter ThompsonIdentification and symptomsAdult swift moths have a wingspan of 30–40 mm withdark brown forewings with white streaks meeting tomake a 'v' shape. The hindwings are plain brown. Asignificant proportion of individuals of both sexes areplain buff or brown with no pattern. The larvae arewhite and the head is orange-red and well protected.They reach 30–40 mm when fully grown.Adult ghost moths have a wingspan of 40–65 mm.The male is silvery white and the female is pale buffwith a series of pale pink markings on the forewing.The eggs are oval and shiny white. The larvae aresimilar to those of the swift moth.MonitoringThere are no recognised ways of monitoring thesepests. Infestations may not be detected until damagehas occurred.© Ray HoldenAdult swift moth© David Kennard PhotographyMale ghost mothFemale ghost mothThresholdsNone established.Swift moth life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec123 4 3Ghost moth life cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec123 43Non-chemical controlLarvae may be killed by cultivation.These pests are attacked by a number of polyphagouspredators, including birds and moles. The larvae mayalso be parasitised by certain species of wasp whicheventually kill the larvae. The larvae continue to feedfor some time after they are parasitised and so cropdamage is not reduced immediately. Larvae may alsobe killed by a fungal disease.To date, biological control has not been investigated in the UK.Insecticide resistanceNone known.Swift moth larva1 Moths. 2 Eggs. 3 Larvae. 4 Pupae.Swift moths emerge in late May/early June and females lay about 200 eggs. Theeggs are dropped singly while the female moth is flying. Young larvae feed in thesummer and autumn but severe damage occurs only during the late autumn andspring of the following year, especially in February/March. The larvae of the ghostmoth usually feed for two years before pupating.135Pests: Moths and butterfliesPests: Moths and butterflies136

Large white butterfly (Pieris brassicae)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceLife cycleImportanceFeeding by the larvae of the large white butterflydamages foliage and can skeletonise leaves,particularly on field margins. Frass (droppings) and thelarvae can contaminate fresh produce.Risk factorsThe larvae hide themselves within plant foliage andinfestations may not be detected until damage hasoccurred. Eggs are usually laid in large numbers ononly a few plants, so these can be severely damagedwhile other plants escape. This species is not such asignificant problem as the small white butterfly,whose larvae are well camouflaged and widelydistributed in the crop.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 Pupae overwinter.2 Adults (1 st generation) emerge from pupae andlay eggs.3 Larvae feed/pupae formed (1 st generation).4 Adults (2 nd generation) emerge from pupae andlay eggs.5 Larvae feed/pupae formed (2 nd generation).The second generation is the most damaging tobrassica crops.© University of Warwick1 241© University of Warwick3 5© Dewar Crop ProtectionLarge white butterflylarvae© University of WarwickLarge white butterfly (Pieris brassicae)Identification and symptomsAdults are white butterflies with a wingspan of60–70 mm. The tips of the forewings are black andthe female has large black spots on the upper surfaceof each forewing.Eggs are yellow and flask-shaped (1.5 mm high and0.6 mm at their base) and laid in batches of 20–100 onthe undersides of leaves.Young larvae are pale green initially but soon becomemottled blue-green. When fully grown, a larva is25–40 mm long and has three yellow longitudinalstripes along the body. It is covered with blackmarkings and has groups of short, stiff white hairs that arise from fleshyprotuberances along the body. When fully grown, the larva leaves the plant andfinds a sheltered site to pupate on a vertical or overhanging surface. The pupa isgrey-green in colour and is attached by a silken girdle.MonitoringAdult butterflies can be captured in yellow water traps or on yellow sticky traps.ThresholdsNone established.© Peter ThompsonAdult large whitebutterflyNon-chemical controlThis pest is attacked by a number of polyphagous predators, including some birdsand large beetles.Natural mortality of larvae can be high, due to a species of parasitic wasp (Cotesiaglomerata) and also as a result of infection by a baculovirus. The small, bright yellowcocoons of the parasitic wasps can often be seen clustered alongside dead ordying larvae from which they have emerged. The larvae continue to feed for sometime after they are parasitised and so crop damage is not reduced immediately.The larvae can be controlled with products based on Bacillus thuringiensis (Bt). Thepossibility of control by inundative releases of egg parasitoids (Trichogramma spp.)has been investigated overseas, as has the use of fungal pathogens but neitherapproach has been evaluated in the UK.Because the eggs are laid in batches and the larvae feed gregariously, it is relativelyeasy to spot plants damaged by large white butterfly and either control the pest byhand-picking them or avoid the affected plants at harvest.Large white butterflyeggsYoung large whitebutterfly larvaeInsecticide resistanceNone known.137Pests: Moths and butterfliesPests: Moths and butterflies138

Leek moth (Acrolepiopsis assectella)Leek moth (Acrolepiopsis assectella)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrots✔ AlliumsPeasField beansSugar beetLettuceLife cycle123ImportanceLeek moth larvae (caterpillars) make ‘shot holes’ infolded leaves and this damage and associated decayrender leeks unmarketable.Risk factorsLeek moth may be more of a problem in warmlocations towards the south of the UK.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec6Adult moths emerge in April and lay eggs (up to100 per female) singly on foliage towards thebase of the plant.The larvae feed during May and June. At first,they mine the leaves, leaving the epidermis intactbut then they bore through the folded leaves tofeed near the centre.The larvae pupate in flimsy silken cocoonsattached to the host plants.4 Adults (2 nd generation) emerge and lay eggs.5 Larvae (2 nd generation) feed.6 Pupae overwinter.1234 6Adult leek mothThere are likely to be two generations in the UK, with the second generationlarvae feeding in August and September.5© Paul KitchenerIdentification and symptomsThe adult moth has a wingspan of 15 mm. Theforewings are slender and narrow and have a variablebrown colour, with paler scales near the apices. Thereis a conspicuous white triangular mark halfway alongthe rear margin of each forewing. The rear margins ofthe forewings are fringed with pale-coloured hairs.The egg is oval-shaped, white, iridescent and about0.4 mm in diameter.The larva is 13–14 mm long when fully grown and hasa brown or yellow head and a yellowish-green bodywith inconspicuous grey-brown patches, especiallyaround the spiracles, and yellow plates on the firstand last segments. The pupa is about 6 mm long andbrown.Mining of the leaves of leeks by young larvae leads topatches of papery, necrotic tissue. Older larvae make‘shot holes’ in folded leaves. Severely damaged leavessometimes rot and if the rotting is extensive the plantwill die.MonitoringMale moths can be captured by pheromone traps.This information can be used to time crop walking todetermine whether treatment is required.ThresholdsThere are no validated thresholds for the UK.Non-chemical controlCrop rotation and locating new crops away frompreviously infested soil are necessary to preventreinfestation. Crop debris can be destroyed to killpupae. Leek moth larvae can be attacked by naturalenemies, including parasitic wasps. Biopesticidesbased on Bacillus thuringiensis can be used to controlthe larvae. The use of insect-pathogenic nematodeshas also been evaluated experimentally and appearsto be effective.Insecticide resistanceNone known.© University of WarwickLeek moth larva© University of WarwickLeek moth damage© University of WarwickLeek moth damage139Pests: Moths and butterfliesPests: Moths and butterflies140

Pea moth (Cydia nigricana)Pea moth (Cydia nigricana)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliums✔ PeasField beansSugar beetLettuce© PGROPea mothLife cycleImportancePea moth is one of the most damaging pests of peasin the UK. The larvae feed on peas inside the pod,with the resulting economic damage largely due tocontamination and reductions in quality.In vining peas, the presence of damaged peas, whichcannot be removed mechanically, can result in croprejection.In combining peas for premium markets, includinghuman consumption and for seed, damaged peas areremoved by the merchant and the price paid to thegrower is reduced in proportion. Reductions in yieldare rarely significant and the presence of damage inpeas for animal feed compounding is not important.Risk factorsAny pea crop in flower or in pod in June or July isliable to attack to a greater or lesser degree.Risk of economically damaging infestations is fargreater where damage in previous crops has beensevere and control may only be justifiable in thesecases.Identification and symptomsThe moths are dull grey-brown with markings at the tipof each forewing. They are approximately 6 mm long,with a wingspan of around 15 mm. The eggs are smalland flattened and are laid singly or in small groups onleaves and stipules of pea plants.The caterpillars are pale yellow with black head and legsand are approximately 10 mm long when mature. Theyhave a brown ring on the prothorax, with eight browndots on the following segments. Each pea pod rarelycontains more than two caterpillars. Overwinteringcocoons are found about 10 cm below ground, whilespring cocoons can be found at the soil surface.Damage from the pest occurs within the seed pods.Damaged pods may appear yellow and ripen early.Opening the pods will reveal one or two caterpillars,partially eaten seeds and frass (droppings).© PGROPea moth larva© University of WarwickPea moth larvaMonitoringPheromone traps that attract males have been developed. Traps are placed withincrops by the middle of May and are examined for moths at two-day intervals. Thetraps are used to time sprays so that larvae are targeted from the time of hatchingto the point at which they enter the pods. This is done with the aid of a computermodel, which helps predict egg development using daily minimum and maximumtemperatures. See www.pgro.org for the latest pea moth alerts.1 Overwinter in cocoon underground.2 Caterpillar emerges to form a second cocoon at soil surface. Pupation occursupon leaving this cocoon.3 Moths emerge in late May/early June and lay eggs on pea plants from earlyJune until mid-August.4 Hatched caterpillars enter young pods to feed.6Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec132 4Fully fed caterpillars bite their way out of their pod and descend to the soil toform a cocoon underground.51ThresholdsDry harvested peas for human consumption: Ten or more moths caught in trapson two consecutive occasions.Vining peas: Traps are used to determine if moths are present. Growers should beguided by the factory fieldsman: even very small infestations can lead to rejection.Non-chemical controlLarge pea moth populations can develop where pea crops are left in the field to fullmaturity. Therefore, areas where combining peas are grown are likely to be areservoir of the moths. In other situations, unharvested green peas should beploughed in before the larvae have left the dried pods. Early maturing and early orlate-sown peas may miss the moth flight period, so may be unaffected. Fourspecies of parasitic wasp and a pathogenic fungus attack the pea moth.Insecticide resistanceNone known.141Pests: Moths and butterfliesPests: Moths and butterflies142

Silver Y moth (Autographa gamma)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoes✔ CarrotsAlliums✔ Peas✔ Field beans✔ Sugar beet✔ LettuceLife cycleThis species cannot survive the winter in the UK.Spring migrants use fast-moving airstreams to travelnorth to colonise host plants in northern Europe fromwinter breeding sites in North Africa and the MiddleEast. Migration patterns vary widely from season toseason, so there is no consistent, predictable patternto population development in much of Europe.It is estimated that 10–240 million immigrants reachthe UK each spring, and that summer breedingresults in a fourfold increase in the abundance of thesubsequent generation of adults, all of whichemigrate southwards in the autumn.ImportanceFeeding by the larvae (caterpillars) of the silver Y mothcan cause damage to plant foliage. Frass (droppings)and the larvae can contaminate fresh produce.Risk factorsLettuce is one of the most susceptible crops. Theeggs are laid singly on susceptible host plants andinfestations may not be detected until damage hasoccurred.Silver Y moth is a migratory pest, so crops in thesouth and east may be more at risk. Large numbersof moths can arrive in crops quite suddenly.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec12 36 145 71 Overwinter overseas.2 Immigrant moths may arrive.3 Peak period of immigration.4 Eggs laid.5 Larvae feed.6 Pupae formed.7 Moths migrate southwards.© Peter ThompsonAdult silver Y mothDepending on when they arrive in the UK, silver Y moths may be able tocomplete more than one generation in some years.Silver Y moth (Autographa gamma)Identification and symptomsAdults are grey to greyish-brown in colour and theforewings have a span of 35–40 mm. There is adistinct silver Y mark on each forewing.Eggs are usually laid singly on foliage. They are oval(0.5–0.6 mm diameter) and white in colour, darkeningclose to hatching. Female moths can lay up to 1,500eggs but usually lay an average of 150–650 eggs.The larvae are 24–40 mm long, green (varying frombright green to very dark green) and have a dark greendorsal line edged with white. A light yellow line runsover the sides. The caterpillars ‘loop’ as they walk.When fully grown, the larva pupates on a leaf within aloose web-like cocoon.MonitoringMale moths can be captured by pheromone traps.Traps sometimes capture very large numbers of malemoths.Moths are also caught in light traps run by mothenthusiasts. In 2013, the first silver Y moths capturedby light traps in Dorset were caught on 26 April (a coldspring). In 2012, which had a warmer spring, the firstsilver Y moths were caught there on 28 March.ThresholdsFor vining peas, the threshold is reached when thecumulative catch (pheromone traps) exceeds50 moths by the first pod stage (GS204).For sugar beet, the threshold is five caterpillars per plant.Non-chemical controlThis pest is attacked by a number of polyphagous predators. The larvae may alsobe parasitised by certain species of wasp or fly, which eventually kill the larvae. Thelarvae continue to feed for some time after they are parasitised and so cropdamage is not reduced immediately. Larvae may also be killed by viruses.To date, biological control with predators or parasitoids has not been investigated inthe UK. Pesticides based on microbial control agents (eg Bt) may be effective.Insecticide resistanceNone known.© Peter ThompsonAdult silver Y moth© Dewar Crop ProtectionSilver Y moth larva143Pests: Moths and butterfliesPests: Moths and butterflies144

Small white butterfly (Pieris rapae)Small white butterfly (Pieris rapae)Crops affectedCerealsOilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuceImportanceFeeding by the larvae of the small white butterfly cancause damage to plant foliage. Frass (droppings) andthe larvae can contaminate fresh produce.Risk factorsThe eggs are laid singly on susceptible host plants,the larvae hide themselves within plant foliage andinfestations may not be detected until damage hasoccurred.The second generation usually causes more damagethan the first.Identification and symptomsAdults are white butterflies with a wingspan of50 mm; the forewings have conspicuous black tips.The female has two small black spots on the uppersurface of each forewing, while the male has oneblack spot in the middle of each forewing.Eggs are yellow and bottle-shaped and laid singly onthe undersides of leaves.The larvae have a green velvety appearance, with adorsal yellow line and elongate yellow patches alongtheir sides and are solitary. When fully grown, a larvais 25 mm. When fully grown, the larva usually pupateson the plant, to which it is attached by a silken girdle.© Peter ThompsonAdult small whitebutterflyLife cycleJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 Pupae overwinter.1 22 Adults (1 st generation) emerge and lay eggs.3 Larvae feed/pupae formed (1 st generation).4 Adults (2 nd generation) emerge and lay eggs.5 Larvae feed/pupae formed (2 nd generation).Adult butterflies of the second generation emerge inAugust and this generation is the most damaging tobrassica crops.34 15© Peter ThompsonAdult small whitebutterfly on kaleMonitoringAdult butterflies can be captured in yellow water trapsor on yellow sticky traps.ThresholdsThere are no current thresholds for small whitebutterfly in the UK.Non-chemical controlThis pest is attacked by a number of polyphagouspredators, including some birds and small beetles.Natural mortality of larvae can be high due to speciesof parasitic wasp. The larvae continue to feed forsome time after it is parasitised and so crop damageis not reduced immediately.The larvae can be controlled with products based onBacillus thuringiensis (Bt). The possibility of controlwith other biopesticides is being evaluated in the UK.© University of WarwickParasitised small whitebutterfly larva© University of Warwick© University of Warwick© University of WarwickInsecticide resistanceNone known.Small white butterflyeggSmall white butterflylarvaSmall white butterflypupa145Pests: Moths and butterfliesPests: Moths and butterflies146

Minor/emerging pestsMinor/emerging pestsFlax tortrix moth (Cnephasia asseclana)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliums✔ PeasField beans✔ Sugar beet✔ LettuceThe caterpillar of the flax tortrix moth ties together theupper leaves of pea plants with a fine web and feedswithin the bunched leaves.Damage can be observed in spring, just beforeflowering, but is not severe and will not cause yieldloss.Caterpillars have usually pupated and the newgeneration of moths left the crop before harvest, sono control is necessary.© PGROFlax tortrix mothdamage147Pests: Moths and butterfliesPests: Moths and butterflies148

Further informationAlerts and bulletinsHDC Pest Bulletin: Sponsored by Syngenta and hosted on the Syngenta website,this bulletin aims to provide growers with topical and valuable agronomyinformation throughout the growing season.www3.syngenta.com/country/uk/en/AgronomyTools/HDCPestBulletinHDC PublicationsAvailable at www.hdc.org.ukHDC Factsheet 04/12: Silver Y moth in vining peas and green beans (2012)149Pests: Moths and butterflies

Pests:Nematodes

Contents – Pests: NematodesSpeciesPageBeet cyst nematode (Heterodera schachtii ) 151Free-living nematodes (eg Trichodorus spp. and Longidorus spp.) 153Potato cyst nematode (Globodera pallida and Globodera rostochiensis) 155Stem nematode (Ditylenchus dipsaci ) 157Minor and/or emerging pests 159Cereal cyst nematode (Heterodera avenae) 159Pea cyst nematode (Heterodera goettingiana) 160Root knot nematode (Meloidogyne spp.) 160Further information 161

Nematodes (Nematoda)Unlike the species in the first four sections, nematodes are not insects, they are adiverse group of slender worms.Life cycleIt is estimated that more than half of nematode species are parasitic. Some, likethose described here, are damaging to plant health. Other species are predatory andmay be purchased as a form of pest control.Defining featuresNematode species are difficult to distinguish and most are too small to be seenwithout magnification.© ADAS© ADASMale stubby root nematodeStubby root nematode headregion, showing curved spearused to penetrate plant roots© ADAS© Rothamsted Research LtdRoot lesion nematodeFree-living nematodePests: Nematodes150

Beet cyst nematode (Heterodera schachtii)Beet cyst nematode (Heterodera schachtii)Crops affectedCereals✔ Oilseeds✔ Vegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuce© BBROImportanceBeet cyst nematode (BCN) is one of the mostimportant pests of sugar beet. It also infests cropsrelated to sugar beet, such as spinach, mangold,fodder and red beet, and can complete its life cycle onsome brassica crops, such as oilseed rape, cabbageand Brussels sprouts.In sugar beet, the nematodes damage the roots andstunt the plants through direct feeding, causing wiltingduring periods of drought. Yield reductions of 30% to60% have been reported, depending on the level ofinfestation.In parts of northern Europe, the yellow cyst nematode(Heterodera betae) is also found. It has not, so far,been found in the UK.Identification and symptomsThe juveniles of these nematodes have slender,transparent bodies and are too small to be seenwithout magnification, measuring 0.5 mm in length.The cysts are lemon-shaped (0.5 x 1 mm) and areinitially white but turn brown as they mature. They canbe seen on the roots of beet from the seedling stageuntil harvest. They can sometimes be seen with thenaked eye but can easily be confused with grains ofsand. It is easier to see them if the roots have beengently washed and magnification is used.Crop damage is usually evident as patches of stuntedbeet, which wilt easily in dry periods. Affected plantsproduce many lateral roots in response to the rootdamage: an effect known as 'bearding'.© BBROBeet cyst nematodedamage© BBROCysts of beet cystnematodeRisk factorsCysts can be spread in soil attached to beet roots,farm machinery or footwear. They are most commonin sandy or peaty soils. Cysts can also be spread byfloodwater.Oilseed rape and other brassica seed crops areparticularly efficient hosts of BCN and can lead to aquick build-up of the pest. BCN is most likely to befound on sites with close rotations of beet and/orbrassica crops and where host weed species, such ascharlock and fat hen, are not controlled.Life cycleCysts in the soil can hatch with or without the presence of hosts but rootstimulants produced by host plants encourage additional hatching and attract thelarvae to the roots.The juveniles move through the roots. After developing into adults, the malesreturn to the soil. The females remain within the root and, after mating, begin toswell, forming cysts. Initially white, the cysts containing eggs and larvae turnbrown and can fall off into the soil to repeat the cycle. Cysts can remain viable inthe soil for many years and each cyst contains up to 600 eggs.The life cycle is affected by soil temperature and is completed in 300 degree-daysabove a base temperature of 10°C. In northern Europe, it can complete two orthree generations per year, depending on weather conditions.151Pests: NematodesMonitoringThe level of BCN infestation in the soil can bedetermined by soil sampling and services are offeredby a number of companies.ThresholdsThresholds vary widely across Europe. In the UK,latest results show an economic benefit from usingBCN-tolerant varieties above two eggs and larvae pergram of soil.Non-chemical controlThe number of cysts in the soil can be reduced bywidening the rotation. Oilseed rape and other brassicaseed crops should not be used as break crops forcereals in rotations that include sugar beet.Nematode-resistant brassica catch crops, such as white mustard and oil radish, aregrowing in popularity. Sown in the autumn, they encourage eggs to hatch but areresistant to colonisation by the juveniles, preventing an increase in inoculum for thefollowing beet crop.Nematode-tolerant sugar beet varieties have been developed for use in the UK andthere are a number on the recommended list. While yields are improving, they arecurrently still lower yielding than conventional varieties in the absence of nematodes.Insecticide resistanceNone known.Bearding symptoms dueto beet cyst nematode© BBROBeet cyst nematodesymptomsPests: Nematodes152

Free-living nematodes(eg Trichodorus spp. and Longidorus spp.)Free-living nematodes(eg Trichodorus spp. and Longidorus spp.)Crops affectedCerealsOilseedsVegetable brassicas✔ Potatoes✔ CarrotsAlliumsPeasField beans✔ Sugar beetLettuce© Rothamsted Research LtdStubby root nematodedamage to sugar beetseedlings© Bayer CropScienceCarrot 'fanging' causedby nematodesImportanceFree-living nematodes (FLN) are important as virusvectors and also reduce crop quality and yield byfeeding on the roots. Stubby root nematodes(Trichodorus spp. and Paratrichodorus spp.) and needlenematodes (Longidorus spp.) are generally consideredthe most damaging free-living species.Stubby root nematodes transmit tobacco rattle virus(TRV) to potato, producing an internal disorder of thetubers called spraing. This reduces tuber quality butdoes not affect yield. In some seasons, this can resultin severe losses, as affected tubers are unacceptablefor sale. Although FLN can also transmit TRV to sugarbeet, its effects are less serious than the damagecaused by the nematodes.Yield reductions can occur in most crops if sufficientnematodes are present but are most common inpotatoes, carrots, parsnips and sugar beet. Yieldlosses of up to 17 t/ha have been estimated in sugarbeet. The quality of root crops can also be reduced bynematode feeding. Root 'fanging' is particularlyimportant in carrots, parsnips and sugar beet.Risk factorsFLN are generally most numerous in sandy and otherlight, open-textured soils. Depending on the species,needle nematodes can be found in soils ranging fromlighter soils in the north of the UK to heavier soils inthe south but they tend to favour relativelyundisturbed conditions.Wet growing seasons and regular irrigation canincrease the incidence of spraing, as the nematodesrequire adequate soil moisture to move betweenplants. Damage in sugar beet is reported to be moresevere in years with heavy rain in May.In potatoes, most infections occur soon after tuberinitiation. Some potato varieties show spraingsymptoms more readily than others.Life cycleStubby root nematodes have an extremely high rate of reproduction when soiltemperatures are between 15°C and 30°C. They feed on a range of crop and noncropspecies throughout the year.Needle nematodes multiply relatively slowly on a range of crop and non-crop species.Several generations occur each year, so both adults and juveniles occur together.Identification and symptomsIn many crops, the feeding of stubby root nematodes causes a proliferation ofthickened, ‘stubby’ roots. This causes poor top growth and reductions in yield, andcan make the plant more susceptible to drought stress and mineral deficiencies.Spraing can be recognised as chestnut-brown arcs, circles or lines through thetuber. Spraing-affected tubers usually produce healthy plants but these can haveshort stems with crinkled, malformed and discoloured leaves, known as stemmottle. The tubers these produce can also contain brown flecks.FLN feeding on tap roots can cause the root tip to die, causing lateral roots to takeover. In carrots, parsnips and sugar beet, this feeding can cause multiple tap rootsto form, known as 'fanging' (in carrots and parsnips) or 'Docking disorder' (in sugarbeet). Affected plants in the field are stunted and healthy plants are often seen nextto stunted plants, a symptom known as 'chick and hen'.MonitoringThe number of FLN in soil can be determined by soil extraction. This service isavailable from a number of accredited laboratories. Some also offer a service to detectthe whether stubby root nematodes are carrying TRV. Soil samples for extractionshould be transported very carefully, as the nematodes are easily damaged.ThresholdsIn sugar beet, it has been suggested that severe symptoms often occur in soilswith Trichodorus populations of more than 1,000 nematodes per litre of soil or withLongidorus populations of more than 100 nematodes per litre of soil.Non-chemical controlIn potatoes, choice of healthy certified seed or propagating stock can help preventintroducing nematodes to a field. In areas of greater risk from spraing, usingvarieties with a lower susceptibility to TRV is recommended. Rotating potatoeswith non-host crops and lengthening the rotations (growing potatoes at least oneyear in six) will help reduce nematode populations. Weeds can act as alternativehosts and a source of TRV.Insecticide resistanceNone known.153Pests: NematodesPests: Nematodes154

Potato cyst nematode(Globodera pallida and Globodera rostochiensis)155Crops affectedCerealsOilseedsVegetable brassicas✔ PotatoesCarrotsAlliumsPeasField beansSugar beetLettuceSASA © Crown CopyrightPCN cysts(G. rostochiensis)Pests: NematodesImportancePotato cyst nematode (PCN) is the most importantpest of potatoes in the UK. There are two species:Globodera pallida (white PCN) and G. rostochiensis(yellow PCN). They damage the roots of potatoes,which can result in poor growth, wilting during periodsof water stress, early senescence and a reduction intuber yield by as much as 80%.Risk factorsThe nematode is mainly spread by the movement ofcysts in soil attached to potato tubers, farm machineryor footwear. Cysts can also be spread by wind andfloodwater.Cultivars vary in their tolerance to PCN, with some stillable to produce an acceptable yield in the presence ofPCN. Varieties resistant to G. rostochiensis areavailable and will help to minimise the build up of PCNbut there is only partial resistance to G. pallida.Life cycleIn the presence of the crop, large numbers of eggshatch in April/May and juveniles infest crop roots.In the absence of the crop, smaller numbers hatch inApril/May and these will die unless they find a host.Nematodes continue to hatch and invade crop rootsover the summer and white/cream coloured cysts canbe seen on the crop roots.Mature cysts become detached from the roots at harvest and can remain in thesoil for up to ten years. Each cyst contains hundreds of eggs.Identification and symptomsThese nematodes have slender, transparent bodies, reaching approx. 1 mm in length.As the females mature, they swell, forming spherical cysts 1 mm in diameter,which are initially white or cream coloured. At this stage, they can usually be seenattached to the roots. As the females mature and die, the cysts develop a reddishbrownhard skin. If infested plants are lifted carefully, the mature cysts cansometimes be seen attached to the roots but usually become detached at harvest,remaining in the soil as a source of infection for future potato crops.The nematodes damage the roots and affect yield, even when no symptoms areevident in the haulm. Roots may be killed with severe infections, resulting inPotato cyst nematode(Globodera pallida and Globodera rostochiensis)stunted, often chlorotic plants with a patchydistribution.MonitoringThe level of PCN infestation in soil can be determinedby soil extraction. This service is available from anumber of accredited laboratories. The need fornematicide treatment is related to the number of PCNeggs/g soil.Under EU Directive 2007/33/EC, seed potatoes orpotatoes for export must only be planted on land thathas been found to be free from PCN infestationfollowing an official soil test. This test must beundertaken by a Plant Health and Seed Inspectorate(PHSI) inspector. The growing of ware potatoes will be PCN cysts (G. pallida)permitted, subject to the implementation of a ControlProgramme (see www.fera.defra.gov.uk/plants/plantHealth)ThresholdsThe Potato Council PCN Model is a support tool that assists in developing anintegrated PCN control plan. To manage PCN population levels (eggs/g) andspecies, varieties, rotation and cultural control methods must be taken intoconsideration and advice sought from an agronomist.– Low – 1–10 eggs/g – Nematicide use is recommended– Medium – 10–20 eggs/g – Nematicide treatment is highly recommended– High – >20 eggs/g – Take into account all factors and, if appropriate, considerother groundNon-chemical controlVarious measures can be adopted to reduce or prevent the risk of nematodesaffecting crops. These include selecting resistant or tolerant cultivars (see theBritish Potato Variety Database, maintained by the Potato Council), using PCN-freecertified seed (in seed crops or potatoes for export), and extending the intervalbetween potato crops and rotations using non-host crops. Volunteer potatoes areprobably unlikely to have a significant effect on high PCN infestations but may helpto maintain infestations at a low level from one crop to the next. Effective controlwill minimise this risk. In the absence of the crop, nematode numbers willgradually decline.Insecticide resistanceNone known.SASA © Crown CopyrightPests: Nematodes156

Stem nematode (Ditylenchus dipsaci ) Stem nematode (Ditylenchus dipsaci )Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrots✔ AlliumsPeas✔ Field beans✔ Sugar beetLettuce© Christine A. Hoepting, Cornell UniversityCooperative Extension Vegetable ProgramStem nematodedamage in garlic (top),with a healthy bulb(bottom) forcomparisonImportanceStem nematode is a destructive pest of a range ofplants. Infested seedlings or young plants becomedeformed.Risk factorsThe spread of nematodes is passive, as they do notmove more than a few centimetres each year. Theymay be transferred in soil or host plants, includingseed. The nematodes may also be spread by rain,flood water and wind. There is a risk of infesting cleanfields by planting or sowing infested plant material.Life cycleStem nematodes live as parasites within plant tissues,where both males and females can occur in largenumbers. Their feeding causes the breakdown of cellwalls. Females lay up to 500 eggs and there are atotal of four moults.The stem nematode can survive, mainly as desiccatedfourth-stage juveniles, for several years. These tend toaggregate at the surface of heavily infested planttissue to form clumps of ‘nematode wool’. Thenematodes become active again when the wool ismoistened. In wet soil, they can live in the absence ofhost plants for more than a year.Identification and symptomsStem nematodes are internal parasites of plants. Theyare slender and colourless and impossible to seewithout magnification. The adult body is just over2 mm long and tapers at each end.The problem is usually identified because of plantsymptoms.Onions: Infested seedlings or young plants becomeswollen at their bases and have malformed andtwisted leaves. Infested tissue has a loose puffytexture and the epidermis is dull in appearance(known as ‘bloat’). Rotting then occurs at soil level, sobadly infested plants can be pulled to leave their rootsin the soil. Eventually, infested plants die.Slight infestations may not be noticed but may hastenthe deterioration of stored bulbs.Sugar beet: The tissues of infested seedlings becomeswollen and spongy, galls may be formed and thegrowing points may become deformed or killed. Newgrowing points then develop, leading to multiplecrowns and small distorted leaves. In the autumn, thedamaged crown may rot, encouraging secondarypathogens. Usually, relatively few plants are affected inany one field.Beans: Damage usually shows as stemdiscolouration.MonitoringSoil testing for the presence of nematodes could beconsidered. Dissection of plant tissue and immersionin water can be used to confirm the presence of thepest. This is only likely to be done by a laboratory.ThresholdsThere are no validated thresholds for stem nematode.The presence of stem nematodes in soil usuallymeans the land is avoided for cropping with onions.Non-chemical controlRaces of stem nematode are highly host-specific, soemploying a three-year crop rotation can deprive thenematodes of a suitable host and starve thepopulation.Because some weeds serve as hosts for nematodes, controlling weeds in fieldsdecreases the number of susceptible hosts and the ability of the nematodes tosurvive and spread.Insecticide resistanceNone known.© Rothamsted Research LtdStem nematodedamage to sugar beet© PGROStem nematodedamage to bean plant157Pests: NematodesPests: Nematodes158

Minor and/or emerging pestsCereal cyst nematode (Heterodera avenae)Crops affected✔ CerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beansSugar beetLettuce© Bayer CropScienceCereal cyst nematode is the main nematode pest ofcereals. In the UK, it is more damaging to oats than toother cereals.Intensification of barley growing from the 1960sonwards led to fears that cereal cyst nematode mightbecome a serious problem in this crop. After initialincreases, however, infestations declined (mainlybecause of fungal parasites of the nematode that arefavoured by intensive cereal growing).Infected crops show patches of stunted plantssometimes tinged with red or purple. Infected oatshave a typical bushy root system. Significantinfestations of cereal cyst nematode are relatively rare.© Bayer CropScienceMinor and/or emerging pestsPea cyst nematode (Heterodera goettingiana)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliums✔ Peas✔ Field beansSugar beetLettuceThe pea cyst nematodeattacks the roots of peaand bean crops, with thelatter rarely showingsymptoms. The pest is notubiquitous and incidencevaries from year to year.© PGROSymptoms begin to appearin early summer before Pea cyst nematodeflowering, with areas of cysts on rootthe crop becoming paleand stunted. Plants yellow, have an uprightappearance, small leaves and may flower prematurely.Pods often fail to develop and plants may dieprematurely. Root systems are often poorly developed and will contain tiny, white,lemon-shaped cysts containing nematode eggs, which later turn brown and canremain viable for up to 20 years.Crops in areas that have a long history of frequent pea cultivation and those onlighter, sandier soils tend to be at greatest risk. Yield losses can be sustained withsoil populations of 5 eggs per gram of soil.Cereal cyst nematode eggs and larvaeCereal cyst nematode damageRoot knot nematode (Meloidogyne spp.)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuceThis is an important plantnematode pest,worldwide. Of the 50described species, only afew infest sugar beet.The life cycle is similar tothat of the beet cystnematode (p. 151) andinfested plants are stuntedand tend to wilt in warm© Rothamsted Research LtdRoot knot nematodesymptomsweather. Root knot nematodes cause galls to form onthe lateral roots of plants. Where early infestations aresevere, plants may be killed.Control methods include the use of granularnematicides, trap cropping, lengthening the rotationand control of weed hosts.159Pests: NematodesPests: Nematodes160

Further informationPotato Council informationPCN calculator: www.potato.org.uk/online-toolboxPotato Council Research Review 276: Free-living nematodes and spraing (2006)HGCA PublicationsAvailable at www.hgca.com/publicationsHGCA Student Report 21: Integrated management of cyst nematodes in oilseedrape (2013)HGCA Student Report 13: New cyst nematode threats to cereals in the UK (2009)Information from other organisationsInformation from Fera is available at www.fera.defra.gov.uk/plants/plantHealthFera Plant Pest Factsheet: Potato cyst nematodes (Fera, 2009)Fera Plant Disease Factsheet: Spraing disease of potato (2009)Information from SRUC is available at www.sruc.ac.ukSAC Technical Note 631: Potato tuber pests (2010)SAC Technical Note 603: Soil dwelling free-living nematodes as pests of crops(2007)161Pests: Nematodes

Pests:Others

Contents – Pests: OthersSpeciesPageSlugs 163Soil pest complex 167Minor and/or emerging pests 169Globular springtails (Sminthurus spp. and Bourletiella spp.) 169Two-spotted spider mites (Tetranychus urticae) 170Further information 171

Slugs (Gastropoda)Unlike the species in the first four sections, slugs are not insects, they aregastropod molluscs. The word “slug” is generally applied to any species ofterrestrial gastropod mollusc that has no (or a very reduced or internal) shell.Life cycleUnlike insects, the juveniles emergingfrom the eggs are very similar to theadult slugs. They do not undergometamorphosisDefining featuresSlugs are legless, unsegmented andboneless. The body of a slug is mademostly of water and, without a shell,they are prone to desiccation.They generate protectiveTailmucus and are usually mostactive on still nights when thesoil is wet and the atmosphereis humid (particularly just afterrain). They hide in damp placesduring drier periods and windand heavy rain can decrease their activity.AdultsJuvenilesMantleFoot fringe Foot Pneumostome(respiratory opening)Soil pest complex(millipedes, subterranean springtails and symphylids)EggsOpticaltentaclesSensorytentaclesWhile not related, these species are grouped together because they can appear atthe same time and cause similar types of damage by feeding on roots, causingseedlings to collapse and die.Life cycleThe life cycle varies foreach species, see p. 167.Defining featuresThese creatures liveunderground and havevariable numbers of legs.Being subterranean, theyare generally white orpale in colour.SubterraneanSpringtailMillipedeSymphylidPests: Others162

SlugsCrops affected✔ Cereals✔ Oilseeds✔ Vegetable brassicas✔ Potatoes✔ Carrots✔ Alliums✔ Peas✔ Field beans✔ Sugar beet✔ Lettuce© ADASGrey field slugsImportanceSlugs can cause damage all year round, wheneverweather and temperature conditions are suitable, butare particularly damaging in autumn crops andpotatoes.Early stages of most affected crops and tubers inpotatoes are most vulnerable. In cereals, seedhollowing is a particular problem. Both cereals andoilseed rape are susceptible to leaf grazing until thefour-leaf stage. In potatoes, slugs affect crop qualityby mining the tubers and providing an entry point forfungal pathogens. Potatoes are most vulnerable at theearly stages of tuber bulking. For vegetables, attack inthe early stages can cause plant loss and, at laterstages, feeding can lead to cosmetic problems.Risk factorsSlug activity, survival and reproduction are dependenton moisture. The optimum temperature is 17°C.Slugs are most abundant in heavy soils with high clayor silt content with open, cloddy seedbeds allowingeasy movement.Damage is much greater after leafy crops. Cropresidues or applications of manure, especially in theautumn, as well as weeds and volunteers, provideslugs with a source of food and shelter.Lack of nutrients, poor drainage and weedcompetition can all result in slow crop growth,prolonging the vulnerable period of establishment.SlugsLife cycleSlugs can be active all year round but the main breeding periods of the grey fieldslug and garden slug are shown below.Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec1 Peak breeding (field slugs).2 Peak breeding (garden slugs).1 2 1All slug species are hermaphrodite (each individual isboth male and female). While some species are selffertile,most mate before laying eggs in batches of 10to 50 in soil cavities, between clods, under stones orat the base of plants.Up to 500 eggs per slug may be laid over severalweeks. Eggs develop slowly in the winter but willhatch within a few weeks when the temperaturestarts to rise.In their lifetime, slugs will travel only a few metresfrom their hatching site, in a circular route, in search offood. They are active and feed throughout the year,whenever conditions are suitable (see risk factors).© ADASSlug eggs© ADAS © Image courtesy of The Food and Environment Research Agency(Fera), Crown Copyright© Jon Oakley © University of WarwickSlug damage in oilseed rape Slug damage in potatoSlug damage to grain Slug damage to lettuce163Pests: OthersPests: Others164

Slugs165© ADASGrey field slug© Jon OakleyGarden slug© Jon OakleyKeeled slug (Milaxbudapestansi)Pests: OthersIdentification and symptomsThe key pest species are:– grey field slug (Deroceras reticulatum and otherDeroceras spp.)– garden slug (Arion hortensis and Arion distinctus)– keeled slug (Milax, Tandonia and Boettgerilla spp.)Grey field slugs are the most common and injuriousspecies. They are usually grey or fawn and adults are35–50 mm.Garden slugs are usually smaller than field slugs, witha dark upper body and a yellow to orange underside.Keeled slugs are generally the largest pest species(50–75 mm) and are grey to dark-brown or black witha ridge down the centre of the back.Slug feeding causes seed hollowing, leaf shreddingand tuber damage. Leaf shredding produces irregularshapedholes in leaves and can be especiallydamaging to seedlings. Slugs scrape a hole in a seedcoat and hollow it out, often resulting in the removalof the cereal germ before it can germinate. Feedingon potato tubers causes ragged holes on the surfaceand larger cavities within the tuber.MonitoringMonitoring is most effective when soil is moist andtemperatures range from 5–25°C. Sampling is bestdone using refuge traps. Traps consist of a cover suchas a an empty sack, carpet square or a tile, with anon-toxic bait, such as chicken layers mash, to assessslug activity. Do not use slug pellets to bait traps.Put slug traps out before cultivation, when the soilsurface is visibly moist and the weather is mild. Ineach field, nine traps (13 in fields larger than 20 ha)should be set out in a 'W' pattern, concentrating onareas known to suffer damage. Leave the trapsovernight and examine early the following morning.Crops should also be monitored regularly for slugdamage. The critical control periods will varydepending on the crop. See the publications listed inthe Further information section for more details.SlugsThresholdsThe following represent potential risk of damage when soil and weather conditionsfavour slug activity:Winter cereals: 4 slugs per trapOilseed rape: 4 slugs per trap in cereal crops or 1 slug per trap in cereal stubbleVegetables: No thresholds establishedOther crops: 1 slug per trapNon-chemical controlPloughing can reduce slug populations but even minimum tillage gives aconsiderable reduction in slug damage compared to direct drilling. A fine,consolidated seedbed is important and will protect seeds and prevent slugsaccessing seedlings before emergence. Increase the sowing depth of wheat to4–5 cm if the seedbed is cloddy.Damage in potato crops is partly related to tuber maturity, even occurring under dryconditions. Lifting the crop as soon as possible can limit damage by minimising thetime the potatoes are exposed to feeding.Phasmarhabditis hermaphrodita is a parasitic nematode that attacks slugs and,unlike pellets, can target soil-dwelling slugs and not just those active on the soilsurface.Natural enemies include ground beetles, rove beetles, parasitoids, birds,amphibians and hedgehogs, so providing habitats for these may help control slugpopulations.Insecticide resistanceNone known.© ADAS © Rothamsted Research LtdSlug infected with PhasmarhabitishermaphroditaSlug damage to sugar beetPests: Others166

Soil pest complex(millipedes, subterranean springtails and symphylids)Soil pest complex(millipedes, subterranean springtails and symphylids)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuce© Rothamsted Research LtdFlat millipede© Rothamsted Research LtdSpringtail© www.aphotofauna.comSymphylidImportanceRarely occurring as a single species, the soil pestcomplex can attack from germination onwards,causing feeding damage to the roots and stem belowthe soil.Damage can sometimes be severe, causing seedlinggrowth to slow and killing some seedlings, leading tobare patches in the field in the spring.Symphilids may also attack crops such as potatoes,tomatoes and lettuce.Risk factorsThe risk is higher in cold, wet springs. The complex ismore common in fields with plenty of fresh organicmatter or an open soil texture.Life cycleMillipedes breed in spring and summer, laying eggsin 'nests' in the soil. The young have three pairs oflegs and add more segments, each with a pair of legs,until they are fully grown after two to three years.Springtails have two breeding peaks per year: one inlate spring and the second in the autumn/winter.Symphylids lay eggs throughout the year in batchesof up to 20. Young symphilids have three pairs of legsand they go through a series of moults, adding a pairof legs each time until they have 12 pairs in total. Thisprocess takes three months and symphylids can livefor several years.Identification and symptomsMillipedes (Blaniulus spp., Brachydesmus spp.,Polydesmus spp. and other species) occur in twotypes: snake and flat millipedes. All have a body withmany segments and each segment has two pairs oflegs. They are approximately 1 mm in diameter andbetween 10 mm and 20 mm in length.Subterranean springtails (Onychiurus armatus andFolsomia fimetaria) are white and have an elongatedbody and, on average, are 1 mm in length.Symphylid (Scutigerella immaculata) adults areactive, with a slender body 5–7 mm in length. Theyare white and shiny, with two long antennae and 12pairs of legs.Some feeding damage is superficial but some can bedeeper, causing pits in the roots, especially beforeemergence. Grazing of the root stem and root hairscauses the seedling to collapse and die. Sites wheredamage has occurred can be prone to secondarypathogenic fungi.MonitoringBare patches in the field may suggest damage by thesoil pest complex. Millipedes and symphylids may beseen in soil samples with the naked eye butmagnification is needed to see springtails.ThresholdsThere are no thresholds to relate numbers to crop damage. Yield loss is due to lossof plants and crops with very low populations may need to be re-drilled withinsecticide-treated seed.Non-chemical controlPlants are less susceptible to attack by millipedes once they are beyond the fourtrue leaf stage.Insecticide resistanceNone known.© Rothamsted Research LtdSpotted snakemillipede167Pests: OthersPests: Others168

Minor and/or emerging pestsGlobular springtails (Sminthurus spp. and Bourletiella spp.)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuceIn contrast to the soil-living springtails, thesespringtails live above ground. They have a globularbody and are light green or purplish in colour.They feed on cell contents through puncture woundson the cotyledons or true leaves, causing superficialdamage, and they are not a serious pest.On the leaf, however, green-coloured springtails mayeasily be mistaken for green aphids. They are readilydistinguished from aphids because they jump whendisturbed.Minor and/or emerging pestsTwo-spotted spider mites (Tetranychus urticae)Crops affectedCerealsOilseedsVegetable brassicasPotatoesCarrotsAlliumsPeasField beans✔ Sugar beetLettuceTwo-spotted spider mites are small, round, yellowishbrownin appearance and have two dark spots on theabdomen.They invade crops from their overwintering hosts onparachutes of silken threads blown in the wind. Assuch, they generally appear first on headlands.Symptoms are yellow spots on the leaf surface and adark colouration underneath often with webs visible.They are visible with the naked eye. Damaged leavesdie and defoliation can occur in severe infestations.Two-spotted spider mites are favoured by warm dryweather. Control is usually by natural predators andthere are no effective treatments against them.© Rothamsted Research Ltd © Rothamsted Research LtdSpider mite and eggSpider mite damage under surface© Rothamsted Research Ltd © Rothamsted Research LtdSpider mite damage early symptomsSpider mite damage severe symptoms169Pests: OthersPests: Others170

Further informationAHDB PublicationAvailable at www.hgca.com/publicationsAHDB Information Sheet 02: Integrated slug control (2013)HDC PublicationsAvailable at www.hdc.org.ukHDC Factsheet 02/09: Slug control in field vegetables (2009)HGCA PublicationsHGCA Research Review 79: Implications of not controlling slugs in oilseed rapeand wheat in the UK (2014)HGCA Research Review 77: Implications of the restriction on the neonicotinoids:imidacloprid, clothianidin and thiamethoxam on crop protection in oilseeds andcereals in the UK (2013)171Pests: Others

Naturalenemies

Contents – Natural enemiesSectionPageUtilising and enhancing natural enemies: the ‘SAFE’ approach 173Beetles (Coleoptera) 175Ground beetles (Carabidae) 175Rove beetles (Staphylinidae) 177Soldier beetles (Cantharidae) 179Ladybirds (Coccinellidae) 180Bugs (Hemiptera) 181Flower and pirate bugs (Anthocoridae) 181Damsel bugs (Nabidae) 182Assassin bugs (Reduviidae) 183Centipedes (Chilopoda) 184Flies (Diptera) 185Robber flies (Asilidae) 185Long-legged flies (Dolichopodidae) 186Balloon and dagger flies (Empididae) 187Dance flies (Hybotidae) 188Dung flies (Scathophagidae) 188Gall midges (Cecidomyiidae) 189Hoverflies (Syrphidae) 190Lacewings (Neuroptera) 191Green lacewings (Chrysopidae) 191Brown lacewings (Hemerobiidae) 191Sawflies, wasps, ants and bees (Hymenoptera) 192Bees, true wasps and ants (Apocrita-Aculeata) 193Parasitic wasps/parasitoids (Apocrita-Parasitica) 194Spiders and mites (Arachnida) 197Money spiders (Linyphiidae) 198Wolf spiders (Lycosidae) 198Predatory mites (Phytoseiidae) 198Further information 199

Natural enemiesNatural biological controlLevels of both major and minor crop pest infestations vary between fields andyears but are frequently regulated by their natural enemies (beneficial insects).Pesticides are only needed when the pests escape this control.To encourage robust control at all times and locations, it is essential that a widerange of natural enemies are present, capable of controlling each of the pest's lifestages. Different species may also work together (act synergistically), for example,parasitic wasps may cause aphids to fall to the ground, where they aresubsequently predated by ground-foraging natural enemies.To maximise pest control, it is important to encourage not only the species playinga major contribution, such as hoverflies (page 190) and parasitic wasps (page 194),but also overall levels of natural enemies providing background levels of control thatprevent pests reaching outbreak levels.Encouraging natural enemiesOn some farms, a diverse landscape with many existing hedgerows and flower-richgrassland provides natural enemies with adequate habitat. Elsewhere, especially inopen simple landscapes and where there are large fields, extra provision is needed.Appropriate management will encourage populations of natural enemies withincrops. Adopting integrated pest management (IPM) principles will ensure thatinsecticide inputs are only applied when necessary, helping to reduce spray costs,preserve natural enemies and prevent insecticide resistance developing.Attributes of an effective natural enemyA suite of regulating organisms, such as invertebrate natural enemies, insectpathogenicfungi, nematodes and other microorganisms, will contribute to thecontrol of a crop pest during each life stage.Effective natural enemies share some common characteristics:– Their primary prey or hosts are pest species– Ability to seek out prey using visual or chemical cues– Can vary their reproductive capacity in response to prey abundance or adversefarming practices– Sufficiently mobile to penetrate the largest fields and reinvade after detrimentalagricultural operations– Consistent densities and ability to survive adverse farming practicesThe main invertebrate orders and families containing the most important naturalenemies of field crops are described here. The level of information available variesbecause some have been studied in more detail than others.Natural enemies172

Utilising and enhancing natural enemies:the ‘SAFE’ approachUtilising and enhancing natural enemies:the ‘SAFE’ approachNatural enemies require appropriate resources to help keep pests in check:SShelter© J M HollandHedgerows, associated margins and othershrubby areas protected from insecticidesand intensive tillage provide habitats thatenable beneficial insects to repopulatenearby crops. Strips of tussocky grasses and flowerrichgrassland support high densities of some species.Natural enemies that only live for part of the yearwithin a crop need other habitats in which to forage,breed or survive dormant periods. Provide shelter for natural enemies by:– managing hedges to create different structures with varied plant species– re-sowing degraded hedge bases covered in noxious weeds, eg ragwort orthistles, with a flower-rich grass mix– protecting natural vegetation along hedge bases and fence lines, frominsecticide and herbicide drift– ploughing two furrows together to form a raised 'beetle bank', creating drierconditions favoured by insects and dividing larger fields – sow with tussockforminggrassesAAlternative preyPests often occur sporadically during thegrowing season. They have shorter lifecycles than natural enemies. Other foodsources (alternative prey) within andoutside fields are needed to maintain natural enemypopulations and can be provided by:– other crops© Dewar Crop Protection– uncropped areas, such as field margins, woodland and less intensivelymanaged grasslandMinimum tillage and application of– undersowingorganic manures are especially– weeds (uncompetitive)valuable in providing suitableconditions for detritus-feeding– minimum tillageinvertebrates which serve as– organic manuresalternative prey for predators.FFlower-rich habitatPollen and nectar are essential for somegroups of natural enemies, especiallyparasitic wasps and hoverflies, and areimportant foods for many other naturalenemies.Woodlands, hedges, margins, crops and agrienvironmenthabitats containing wild flowers, annualarable plants or flowering wild bird seed plants cansupply pollen and nectar. These flower-rich areas alsosupport alternative prey.Flower-rich areas can be created using either a mix ofwild flowers and grasses or legumes. Mixes thatprovide both complex and simple flowers are themost beneficial as these support both short- andlong-tongued insects.EEnvironmentInsect natural enemies thrive in diversevegetation that has not been treated withinsecticides, such as field margins. Allapproved insecticides affect them to somedegree, so it is important to minimise usage byadopting integrated pest management and onlytreating when thresholds are reached. Otherpesticides may adversely affect natural enemies,directly or indirectly, for example, removal of weedyhabitats.© Helen Martin, Rothamsted Research© John Holland, GWCTCorrect management will help create a habitat structure providing naturalenemies with cover and a suitable microclimate. The first step to maximisebenefit from natural enemies is to manage habitats so that they:– are spread across the farm – some natural enemies tend to remain close tomargins– are diverse – this encourages a range of natural enemies providing robustbiological control173Natural enemiesNatural enemies174

Beetles (Coleoptera)Beetles occur in all types of habitats and are among the commonest insects onfarmland. Larvae usually live in the soil or in dead wood. Most adult beetles can fly,although they spend the majority of their time on vegetation or on the ground.There are many beneficial beetle species that feed upon crop pests or contribute topollination but also some pest species (pages 16 to 41). They are also important inthe diet of farmland birds and some mammals.Ground beetles (Carabidae) – 350 speciesIdentificationEggs are ovoid and usually laid singly in or under thesoil.Larvae are elongated with biting mouthparts, threepairs of legs, each of which has six segments withtwo claws at the end and ten abdominal segments.They can be confused with rove beetle larvae butground beetle larvae have more flattened heads.Adult ground beetles are of variable size (2–25 mm),typically black or brown, often with metallic sheens;some are brightly coloured. They have bitingmouthparts and are normally seen running on theground. Most are flightless and they are usuallynocturnal.Life cycleWithin the ground beetles, there are varying lifehistories breeding either in the summer/autumn andthen overwintering as larvae, or breeding in the springand overwintering as adults. Others have flexiblebreeding times according to the weather, while somehave prolonged resting periods as adults. The life cyclecan last from one to several years, with between twoand five larval stages. Larvae are carnivorous with theexception of Harpalini which feed upon seeds. Adultsusually overwinter outside of the crop in field marginsor woodland, whereas larvae are also foundoverwintering within fields at densities of up toone million/ha.© Jon OakleyCarabid larva© Kevin McGeeThe generalistpredator, Poeciluscupreus© Kevin McGeeA seed-feeding beetle,Ophonus ardosciacusGround beetles (Carabidae) – 350 speciesBenefitsApproximately 20–30 species are important forbiocontrol; 5–10 are abundant on farmland. Beetlesoverwintering outside of the crop reinvade in thespring to help control pests but most remain within60 m of the edge and, consequently, coverage oflarge fields may not be achieved.Ground beetles are regarded as generalist predators,providing a background level of control for a widerange of pests such as aphids, fly eggs and larvae,moth/butterfly eggs and larvae, slugs and weedseeds. They also act synergistically with other naturalenemies, for example, consuming pests droppingfrom the crop as they try to escape other predators orparasitoids.StatusAlthough still abundant on farmland, numbers havedeclined with the advent of intensive farming. Theyare killed by most foliar-applied insecticides andintensive soil tillage.How to encourageTechniques to encourage ground beetles include:– dividing large fields (>15 ha) with beetle banks toensure a more even coverage– having field margins containing tussock-forminggrasses– reducing the intensity of soil cultivations (minimumtillage)– using spray thresholds to reduce insecticideapplications– allowing uncompetitive weeds to survive within thecrop: low levels of weeds within crops also helpsupport ground beetles by providing cover andalternative food (insects and seeds)© Jon OakleyThe common, grounddwellinggeneralistpredator, Pterostichusmelanarius, whichoverwinters as larvaein fields© Jon OakleyThe climbing predator,Demetrias atricapillus,which overwinters infield margins© Kevin McGeeThe ground-dwellingpredator, Agonummuelleri175Natural enemies: BeetlesNatural enemies: Beetles176

Rove beetles (Staphylinidae) – approximately 1,000 speciesRove beetles (Staphylinidae) – approximately 1,000 speciesIdentificationEggs are white and either round or pear-shaped.Larvae are elongate with three pairs of legs, each ofwhich has five segments with one claw.Adults are of variable size (1–25 mm), elongate withflattened bodies, typically with short wing cases thatdo not cover the abdomen, although this is not uniqueto this family. Some have distinctive colours, usuallyred and black, and are easy to recognise (seeTachyporus hypnorum) but most are black andindistinguishable. Most species can fly and climb well.They can be confused with earwigs.Life cycleThe breeding period of rove beetles varies betweenspecies, smaller ones breed earliest from Februaryonwards and continue through to winter. For mostspecies, adults emerge between May and August.Depending on the species, they overwinter either aslarvae or adults. Larval stages are typically short: afew days to weeks but the adults are longer-lived.BenefitsThe huge diversity of species has resulted in a broaddietary range and includes species that arescavengers, generalist and specialist predators, fungalfeeders, leaf and flower feeders and parasitic (seeAleocharinae box on the following page).Approximately 40–50 species are important forbiocontrol, 5–10 are abundant on farmland.In agricultural crops, the commonest species areomnivorous. The insect prey is frequently the eggsand larvae of flies, moths, butterflies, springtails andaphids. Rove beetles are in turn consumed by otherinsects, amphibians, reptiles, birds and bats.© Josef DvorakTachyporus hypnorumfeeds on insects andfungi and overwintersat base of tussockygrasses© Kevin McGeePhilonthus cognatus,one of the largerfarmland rove beetles,overwinters in fieldsStatusOnce numerous on farmland, numbers have declined sharply in recent decades,especially fungal-feeding species, such as the Tachyporinae, possibly due tofungicide use. Rove beetles are especially vulnerable to insecticide sprays appliedin the spring and autumn. Ploughing may not directly reduce numbers but rovebeetle abundance and species diversity is higher with minimal tillage, due toindirect effects (more surface litter, weeds, soil moisture, fungi and detritivores).How to encourageThey occupy most habitats, including crops, grassland and woodland. Rove beetlesoverwinter outside the crop in sheltered places, such as under rocks and bark or ingrassy tussocks, or as larvae in the soil at densities of up to 0.5 million per hectare.The same methods used to encourage ground beetles will also favour rovebeetles, especially reduction of all pesticide inputs as they are considered moresensitive.For high value nursery crops, Atheta coriaria can be reared and released for thecontrol of sciarid and shore flies and potentially western flower thrips.AleocharinaeTheir life cycles are highly variable according totheir food. Many are generalist predators living onor in the soil but some are known to predate orparasitise crop pests or feed on fungi, such asmildew, on cereals.This is a very diverse group of insects, common inmost habitats, including farmland. Most are small,3–5 mm, although they range in size from

Soldier beetles (Cantharidae) – 41 speciesIdentificationLarvae are dark brown or grey, sometimes with avelvety appearance, highly segmented, almost wormlike.Narrow elongated beetles (2–15 mm) with soft bodieswhose name arose from the similarity of the redcolouredspecies to military uniforms. The wing-casesare long, thin and covered with short dense hair thatgives them a dull, matt appearance. The adults can bebrightly coloured either yellow or red (as in RedSoldier beetles), or are dark–brown or black (known asSailor beetles) sometimes with yellow tipped wingcases.Adults are good flyers and larvae are capable ofmoving from margins into fields.Life cycleOne or two generations are produced each year.Adults feed predominantly on nectar, pollen andhoneydew but can be carnivorous, feeding on live anddead soft-bodied insects, such as caterpillars, spidermites and aphids. They are often seen on flowerheads of umbellifers at mating time.BenefitsLarvae feed on vegetation but are rarely pests and,when larger, prey on fly larvae, caterpillars andearthworms.Adults are carnivorous and feed on other flowervisitors.Five species are important for biocontrol, three areabundant on farmland.© Jon OakleyRhagonycha fulva istypically seen matingon cow parsley andhogweed flowers© Kevin McGeeThe adults and soilactivelarvae ofCantharis livida arepredatoryLadybirds (Coccinellidae) – 53 speciesIdentificationEggs are easily recognisable, usually elongate, ovalshapedand laid end up in batches. Their colour variesbetween species varying from light yellow to darkorange.Larvae are brightly coloured and have a distinctiveappearance. They are commonly seen feeding onaphids in crops.Adults (1–10 mm) are, typically, brightly coloured(yellow, orange or scarlet), usually with patterned (spots,bands or stripes) wing covers, domed bodies and short,club–shaped antennae.Life cycleThe life cycle usually lasts about one year, occasionallythere are two generations per year. Eggs are laid inspring to early summer, close to their larval prey.Pupation occurs mid-summer and adults emergemid–late summer. With sufficient food and warmth,larval development is faster and two generations peryear are possible. They overwinter as adults in shelteredplaces, such as in leaf litter, grass tussocks, barkcrevices and buildings. They emerge in spring and seekout mates.© Jon OakleyBenefitsTheir most common food is aphids and scale insects,although a few species feed on fungi and the 24-spotfeeds on plants. Five species are considered importantfor the control of aphids on cereals, potatoes and sugarbeet. Ladybirds are good flyers; however, adultdispersal is random and it is only when they settle on aplant that more systematic searching occurs aided by olfactory cues.The larva of the nonnative,invasiveHarlequin ladybird© Jon OakleyLarva of the 7-spotladybird© S Nygaard © G San MartinLeft: Adult 7-spotladybirdRight: Adult creamspot ladybirdpreparing to flyStatusAbundant in meadows and flower-rich field margins, they are frequently observedvisiting umbellifer flowers, for example, cow parsley.How to encourageLarvae prefer dense vegetation and cover crops in winter may encourage larvaeinto arable fields from field boundaries. Flower-rich habitats, especially thosecontaining umbellifers, will attract adults.StatusThreatened by the invasion of the non-native Harlequin ladybird, which competesfor food and consumes the larvae of native ladybirds.How to encourageAdults are attracted to simple open flowers, for example, wild carrot, angelica andyarrow, where they feed on nectar and pollen. The use of broad spectruminsecticide sprays should be avoided.179Natural enemies: BeetlesNatural enemies: Beetles180

Bugs (Hemiptera)Bugs include true bugs (Heteroptera), aphids and whiteflies (Sternorrhyncha) andhoppers (Auchenorrhyncha).Natural enemies are only found in the Heteroptera; their contribution to pestcontrol is unknown. Of the carnivorous families, only Anthocoridae and Nabidae,occasionally Reduviidae, occur on farmland.Flower and pirate bugs (Anthocoridae) – 33 speciesIdentificationFlower and pirate bugs are difficult to identify tospecies level. They are small (2–6 mm) and generallyflattened, oval or long with a head with a parallel-sidedsnout. The end antennal segment is coloured.Life cycleThere are one to three generations per year and theyoverwinter as adults. Eggs are laid singly just beneaththe surface of their prey's host plant. Each femaletypically lays 50 or more eggs and there are fivenymphal stages, reaching adulthood in about 50 days.BenefitsNymphs are predatory and can consume up to 240aphids. Most adults are highly mobile and seek outtheir prey, making them effective predators. They aremost commonly found on trees and shrubs, wherethe larvae and adults feed on eggs, immature andadult stages of immobile insects, such as thrips,aphids, mites and whiteflies. Some are specialisedand are capable of feeding on leaf-mining caterpillars.© Koppert Biological SystemsAdult flower bug(Anthocoris nemoralis)© Jon OakleyFlower bug nymphDamsel bugs (Nabidae) – 12 speciesIdentificationAll species are brown, slender with long legs and afour-segmented beak. They are approximately6–12 mm long.Life cycleDamsel bugs have one generation per year, althoughthey are capable of producing hundreds of eggs laid inrows of 5–10 on plant stems. They have either four orfive nymphal stages, overwintering either as eggs oradults.BenefitsThe adults are frequently flightless but they are stillmobile, aggressive predators that feed on a widerange of insects. They are found on plants on theground and in margins, shrubs and trees.StatusUnknownHow to encourageThey may benefit from floristically diverse fieldmargins and non-crop habitats that contain alternativeprey.© Kevin McGeeMarsh damsel bug(Nabis limbatus)© J K LindseyDamsel bug (Nabisrugosus)© Jon OakleyStatusUnknown© Koppert Biological SystemsHow to encourageThey may benefit from floristically diverse fieldmargins and non-crop habitats that contain alternativeprey.Adult flower bug(Orius insidiosus)feeding on thripsDamsel bug nymph(Himacerusmirmicoides)181Natural enemies: BugsNatural enemies: Bugs182

Assassin bugs (Reduviidae) – 8 speciesCentipedes (Chilopoda) – 57 speciesIdentificationAssassin bugs can be large (4.5–18 mm) and have ashort, curved rostrum.© Roger KeyIdentificationCentipedes are not insects but belong to themyriapods, meaning ‘many legs’.© Jon OakleyLife cycleThey have one to two generations per year, althoughthey sometimes take more than one year to reachmaturity. Assassin bugs overwinter as eggs, larvae oradults.They have a variable number (always odd) of flattenedsegments, each bearing a pair of legs. The first pair oflegs are modified to form a pair of pincers that injectvenom into their prey. They are typically a drab browncolour and 30–60 mm long.BenefitsLarvae and adults are predators of immature and adultstages of flies, beetles and caterpillars. They inject alethal saliva for extra-oral digestion. They may also bitehumans.StatusUnknownHow to encourageThey may benefit from floristically diverse fieldmargins and non-crop habitats that contain alternativeprey.Thread-legged bug(Empicorisvagabundus)In contrast, millipedes are vegetarians and have twopairs of legs on each segment.Life cycleEggs are laid singly or in batches and are cared for bysome species. The larvae develop through a series ofmoults into adults. Generation time is usually one yearbut adults may live for several years.BenefitsMost are predatory, living in the soil, dead wood orleaf litter and predating any soft-bodied insects andearthworms.StatusUnknown.Variegated woodlandcentipede© J McMillanHow to encourageUnknown.Western yellowcentipede183Natural enemies: BugsNatural enemies: Centipedes184

Flies (Diptera)The diptera is a very diverse order, with just over 7,000 species. Flies occureverywhere and are commonly known on farmland, where they may be pests(pages 80 to 125), pollinators or natural enemies.Although there are numerous predatory species that are very common onfarmland, relatively little is known about their ecology and contribution to pestcontrol, except for the hoverflies (page 190). Likewise, many species may pollinateflowers but their overall importance for pollination is poorly understood. They alsocontribute to nutrient recycling of dung and vegetation.Robber flies (Asilidae) – 29 speciesIdentificationAdults are of variable size, 3–50 mm (typically9–15 mm) and vary in shape from long and slender toshort and stout. Likewise, colourings are variable,sometimes with yellow or orange markings on thebody, similar to the markings of wasps and bees(warning signs). They are relatively rare on farmland.Life cycleThe number of generations per year varies from oneto several, depending on the species.BenefitsThe larvae predate the larvae of other insects, eitherin the soil or in decaying wood. Adults are agile flyers,capable of catching other insects on the wing andspiders. They are found in most types of uncroppedland on farmland. Two species are consideredimportant for biocontrol.© Kevin McGeeRobber fly (Dioctriabaumhaueri) with prey© Ian AndrewsLong-legged flies (Dolichopodidae) – 287 speciesIdentificationAdults are small, 1–9 mm, with long slender legs.They generally have metallic green bodies, althoughthey can be yellow, brown or black. The wings areopaque or with dark areas towards the tips.Life cycleLarvae develop in the soil, on dead organic matter orin crevices on trees and are predatory or are leafminers. The number of generations per year isunknown. The adults are strong flyers.BenefitsLarvae may predate small soil-inhabiting insect pests.Adults are very common in field margins and crops,predating small invertebrates including pest aphids,midges, thrips and other fly larvae or adults or onlyfeed on floral resources. Six species are important forbiocontrol.StatusUnknownHow to encourageTechniques to encourage long-legged flies include:– providing field margins with a diverse range of flowering shrubs and herbaceousplants– avoiding cutting in the summer– preventing pesticide drift into margins© Jon OakleyLong-legged fly(Dolichopus sp.)© Kevin McGeeLong-legged fly(Poecilobothrusnobilitatus)StatusUnknownHow to encourageRobber flies favour open, sunny habitats, comprisinggrassland and shrubs or hedgerows.Robber fly (Dioctriarufipes)185Natural enemies: FliesNatural enemies: Flies186

Balloon and dagger flies (Empididae) – 208 speciesDance flies (Hybotidae) – 175 speciesIdentificationBalloon and dagger flies are distinguished by theirsmall round head, large eyes and humpbacked thorax.Shapes vary from slender to robust and they vary insize from tiny to large (1–12 mm).Life cycleThe life cycle of these flies is poorly understood. Thereis probably one generation per year.BenefitsLarvae are predatory on other insects in the soil ordead wood or are aquatic.Adults are typically predatory, with strong, piercingmouthparts and predate aphids, psyllids, whiteflies,coccids, midges, thrips and mites, although theircontribution to pest control has not been quantified.Adults of some species feed on pollen and nectar buttheir contribution to pollination is unknown.Six species are considered important for biocontrol.StatusBalloon and dagger flies are very abundant in fieldboundaries and some crops.How to encourageTechniques to encourage balloon and dagger fliesinclude:– providing field margins with a range of floweringshrubs and herbaceous plants– avoiding cutting margins in summer– preventing pesticide drift into margins© Jon OakleyBalloon and dagger fly(Empis entomophthora)© Jon OakleyBalloon and dagger fly(Empis sp.)© Jon OakleyBalloon and dagger flywith preyIdentificationDance flies are small (1–6 mm) and their shapes varyfrom slender to robustly built. They have a humpedthorax and are very similar to Empididae but smaller.Life cycleA dance fly completes one or two generations per year.Dung flies (Scathophagidae) – 54 speciesIdentificationColour varies from dullish yellow-brown to black and/or yellow.The shape varies from slender to robust and the size from smallto large (3–12 mm). The flies have bristly bodies and legs.Life cycleDung flies have a diverse range of life cycles, depending onlarval feeding habitats. The number of generations per year isunknown.BenefitsLarvae feed on plant leaves and flowers, detritus, dung or eggsof aquatic insects. Adults are predatory on soft-bodied insects,often associated with dung. Six species are consideredimportant for biocontrol.Status Unknown© Jon OakleyDance fly (Platypalpussp.) with orange wheatblossom midgeBenefitsAdults are mostly predatory on small insects, such as aphids and midges, incereals and oilseed rape. The larvae are predatory and live in the soil, dead wood ororganic detritus. Four species are considered important for biocontrol.StatusDance flies are often highly abundant along field boundaries and within fields.How to encourageTechniques to encourage dance flies include:– providing field margins with a range of flowering shrubs and herbaceous plants– avoiding cutting margins in summer– preventing pesticide drift into margins© J k LindseyAdult dung fly© S. RaeHow to encourageDung flies are favoured by mixed farming systems where dung is available.187Natural enemies: FliesNatural enemies: Flies188

Gall midges (Cecidomyiidae) – 620 speciesIdentificationMidges are hard to identify to species, although thefamily can be distinguished by their broad, round,often fringed wings. They are minute to tiny(0.5–3 mm).Life cycleTwo to three generations per year are typical. Adultsonly feed on nectar or honeydew. Overwinteringoccurs in the soil.BenefitsThe pest midge species and those that form galls aremore commonly known; however, at least fivespecies have larvae that feed on aphids and otherspredate mites.Of the aphidophagous species, each female can lay50–150 eggs close to the aphid colony; each larvaecan consume up to 80 aphids.Adults of some species are also predatory.StatusUnknownHow to encourageField margins with a diverse range of flowering shrubsand herbaceous plants provide a source of nectar foradults.A few species are reared and released for biocontrolprogrammes in protected crops, strawberries andornamentals; for example, Aphidoletes aphidimyza foraphid control and Feltiella acarisuga for spider mitecontrol.© Koppert Biological SystemsGall midge larvafeeding onpeach–potato aphids© Dan LeederGall midge larvaefeeding on aphidsHoverflies (Syrphidae) – 274 speciesIdentificationEggs are ovoid and laid singly or in groups depending onthe species.Predatory larvae are coloured unlike other fly larvae,which are white or dirty yellow.Pupae can sometimes be found attached to leaves.A wide range of colours is found in adults, althoughspecies with predatory larvae are black with white oryellow spots or bands similar to bees and wasps.Shapes vary from slender to stout and size varies fromsmall to very large (3.5–35 mm). They are characterisedby their ability to hover.Life cycleA highly diverse group with wide-ranging life histories.Generation time is, typically, one or several per yearalthough it can be longer. Adults are highly mobile,capable of migrating hundreds of miles.BenefitsThey are highly effective predators because of theirmobility and short generation time, capable ofpreventing aphid outbreaks. Aphids are the predominantprey of species with predatory larvae and each canconsume up to 1,200 aphids. The larvae are largelynocturnal, so rarely seen on plants. Larvae of otherspecies feed upon fungi, plant parts, detritus or areaquatic. Adults feed upon pollen and nectar of simpleopen flowers, usually white or yellow, such as© Jon OakleyHoverfly larva and peaaphid© Jon OakleyHoverfly (Episyrphusbalteatus) pupa© Jon OakleyHoverfly (Episyrphusbalteatus) adultumbellifers and daisies, and assist with pollination. Six species are important forbiocontrol, two of which are very abundant.StatusNumbers are declining, especially of those species with one generation per year.How to encourageAdults can be attracted into a locality by planting appropriate flower-rich habitats butwill only remain if suitable densities of aphid prey are available. Hoverflies feed onthe flowers of annual arable plants (eg cornflower, chickweed, knotweeds andshepherd’s purse) and hedgerow plants (wild carrot, cow parsley, hogweed andwhite campion). In addition, flower strips can be established specifically for hoverfliesin and around fields containing coriander, buckwheat, phacelia or alyssum.189Natural enemies: FliesNatural enemies: Flies190

Lacewings (Neuroptera) – 69 speciesIdentificationEggs are laid in groups, attached to vegetation. Larvaehave distinct arrow-shaped brown bodies with largepincers. They sometimes attach remains of their preyto their backs as camouflage. Adults have large,translucent wings that are held roof-like above theirbodies. Their wings are longer than their bodies.Life cycleLacewings are capable of producing several generations per year. Eggs can developin 6–30 days and are followed by three predatory larval stages. Larvae may alsofeed on extrafloral nectaries. Pupation occurs in a cocoon on plants andoverwintering can occur in this stage or as adults.BenefitsThe prey of larvae and adults is usually soft-bodied insects, especially aphids,although adults may also consume nectar, yeasts, pollen and honeydew.Lacewings are capable of responding to chemical cues associated with aphids. Thenumber consumed by each larva varies but can exceed 1,500. Their effectiveness incontrolling aphid outbreaks is, however, uncertain.StatusUnknown© Jon OakleyLacewing larvaHow to encourageAdults may be attracted by flower-rich areas and plants supporting aphids. They areknown to be attracted to strips of buckwheat. There are two important families forpest control (shown below).Green lacewings (Chrysopidae) – 20 species– Green bodies and golden eyes– 20–25 mm long– Females lay 150–600 eggs each© Jon OakleyChrysopa perlaSawflies, wasps, ants and bees (Hymenoptera)This order of insects is the largest, comprising 57 families, and encompassesinsects with very different life forms and biologies.The order is divided into three suborders:Apocrita-Aculeata– Stinging insects– Slender-waisted– Includes social insects, such as bees, wasps andants– Also includes some solitary predatory wasp speciesApocrita-Parasitica– Parasitic wasps– Slender-waisted– In many situations, the most important group ofnatural enemiesSymphyta– Sawflies and woodwasps, some of which are pests– Plant-feeding– No obvious waist© Jon OakleyHornet© Jon OakleyParasitoid wasp(Stenomalus micans)© Peter ThompsonWhite-tipped sawfly,Taxonus terminalisBrown lacewings (Hemerobiidae) – 31 species– Brown or grey bodies– 6–25 mm long– Less noticeable than green lacewings– Females lay 600–1,500 eggs each191Natural enemies: Lacewings© Jon OakleyHemerobius nitidulusAdult hymenoptera require proteins for egg development and most feed onhoneydew, nectar or other plant secretions.Adults of some species are carnivorous (eg ants, vespid wasps and some sawflies).The feeding habitats of the social insects are more complicated and may involve thecollection and storage of plant and animal food or culturing of fungi and other insects.Natural enemies: Sawflies, wasps, ants and bees192

Bees, true wasps and ants (Apocrita-Aculeata)Within this suborder there are some parasitic species but in these cases the eggsare laid near the host and the larvae attack the host from the outside.Solitary wasps(Crabronidae) – 118 species– Adult females will take other insects, including othernatural enemies, to feed their young in nests– Their contribution to biocontrol is unknownBethylid wasps(Bethylidae) – 22 species– Ectoparasites of beetle (including stored productpests), moth and butterfly larvaeAnts(Formicidae) – 60 species– Some species are predatory, while others `farm’aphids– Confined to uncultivated landTrue wasps(Vespoidae) – 7 species– Feed their young on other insects– Very powerful jaws– Notched crescent-shaped eyes, wings foldedlengthwise at rest– Eat pollen but do not have nectar - sucking mouthparts193© S. RaeNatural enemies: Sawflies, wasps, ants and beesCrabronid wasp(Nysson spinosus)© T. RansomBethylid wasp© Jon OakleyBlack bean aphidsattended by ants(Myrmica sp.)© Jon OakleyCommon wasp (Vespavulgaris)Parasitic wasps/parasitoids(Apocrita-Parasitica) – over 6,000 speciesIdentificationMost adult parasitoid insects are small and theiridentification is difficult and requires magnification.In some cases, it is possible to identify when the hosthas been parasitised, for example, mummified aphidnymphs and adults or by changes in egg colouration.Such changes can be used to gain an insight into theproportion of parasitised pests and whether chemicaltreatments are needed.Life cycleGiven the huge number of parasitoid species, it is notsurprising that there is a diverse array of differentways in which parasitoids have evolved to coexist withtheir hosts.The larvae of parasitic hymenoptera are usuallyendoparasites (the egg is laid on or inside the hostand the larvae consume it, usually killing it) and suchinsects are called parasitoids. There are also examplesof ectoparasites, which feed outside of the host'sbody, and some that parasitise plants (eg gall wasps).In a few cases, there are species with plant-feedinglarvae (eg Agaonidae and Cynipinae) or with predatorylarvae.Adults feed on nectar, pollen and honeydew, althoughfemales of at least 17 families also feed on theirhosts, consuming body fluids. The amount and qualityof adult food can, in some cases, extend the adult'slifespan and increase fecundity.Adult parasitoids often emerge in areas devoid of theirhosts, so they first locate their host's habitat usingchemical and physical parameters. Once in the righthabitat, the adults search systematically for their hostsusing chemical cues originating from their host. This isthen followed by a process to determine hostsuitability and acceptance.Parasitoids overwinter within their host, eithercoinciding their development with that of the host, oraltering the host's development for their ownpurpose.© Jon OakleyMummified potatoaphid© Jon OakleyParasitoid wasp(Macroglens penetrans)Natural enemies: Sawflies, wasps, ants and bees194

Parasitic wasps/parasitoids(Apocrita-Parasitica) – over 6,000 species195© Koppert Biological SystemsParasitoid laying eggs in an aphidBenefitsAlmost every life stage of each insect species is parasitised by one or more wasps;even the parasitic wasps can be parasitised by hyperparasitoids. Each parasitoidspecies, typically, attacks a specific host species or closely related group ofspecies. They have developed venoms to immobilise their host and an ovipositorthat can place eggs very precisely within or on the host.Parasitoids are important in the control of most pests, with those from theIchneumonidae and Braconidae (superfamily Ichneumonoidea) being the mostimportant, comprising over 3,000 species. The other common superfamily inagricultural crops is the Chalcidoidea, most of which are parasitoids, often of eggs.Parasitoids can control the sex of their offspring and, consequently, the number offertile females and infertile males. Some species can also produce eggs thatcontinue to divide after laying, producing more than one larva. These attributes givethem the ability to respond to their environment by controlling their reproductiveoutput.Natural enemies: Sawflies, wasps, ants and beesParasitic wasps/parasitoids(Apocrita-Parasitica) – over 6,000 speciesStatusCereal pestsCereal aphids 8Number ofimportant parasiticspecies (abundant)Orange wheatblossom midge 4 (3)Yellow wheatblossom midge 3Frit fly 91 (2)Gout fly 2Yellow cereal fly 0Wheat bulb fly 2Cereal leaf beetle 3Cereal groundbeetleunknownWirewormunknownCereal stem sawfly 2Leatherjackets 2Slugs 10–20How to encourageParasitoids are, in some cases, capable of providingsufficient control to prevent pest outbreaks alone,although it may be necessary to adopt specific cropmanagement practices to ensure this occurs.Given their small size, dependence on pests as hostsand preference for floral resources that are usuallylocated on the top of the canopy, parasitoids are veryvulnerable to the direct and indirect effects ofpesticides. Only spray when thresholds are exceededand avoid drift into uncropped areas.Parasitoids may benefit from supplies of nectarprovided by simple open flowers, such as those onbuckwheat and umbellifers. Alternative host speciesmay be needed outside the crop growing season.Parasitoids are weak flyers and for the species that overwinter in the soil(parasitoids of pollen beetle), adopting minimum tillage and planting crops nearbyto the previous year's location will improve parasitism rates.Natural enemies: Sawflies, wasps, ants and beesOilseed rape Number ofpestsimportant parasiticspecies (abundant)Cabbage aphid 3Peach–potato aphid 2Brassica pod midge >20 (2)Cabbage root fly 2Cabbage stemflea beetle 8 (1)Cabbage flea beetle 4Rape winterstem weevil 4 (2)Seed weevil >20 (3)Cabbage stemweevil 6 (1)Rape stem weevil 3 (1)Pollen beetle 9 (3)Turnip sawfly 2Slugs 10–20© Jon OakleyParasitoid wasps oncow parsley196

Spiders and mites (Arachnida)IdentificationSpiders are arachnids, not insects; they have four pairs of legs, no wings and noantennae. They have only two body regions. Harvestmen are most likely to beconfused with spiders. In harvestmen, the two parts of the body are broadlyjoined, whereas in the spiders the body is clearly divided into two parts joined by anarrow stalk. Harvestmen have only two eyes, whereas spiders have six to eight.Spiders and harvestmen are generalist predators and, consequently, may alsocapture other pest natural enemies. They provide background levels of control butthe more mobile species only settle in locations with sufficient prey so exhibitsome response to prey densities.Life cycleThe generation time varies hugely between species, from short-lived species withmultiple generations per year to those that produce one generation per year andlive for several years. Eggs are laid in clutches inside a silk sac and emerge asspiderlings, which in some species are cared for by the female. Spiderlings passthrough several moults before reaching adulthood. Some spiders are capable ofdispersing over large distances by spinning a long thread on which they are carriedby air currents, known as ballooning.BenefitsSpiders are carnivorous and are unique in having a spinner near the hind end of theabdomen that produces silk. Some spiders spin webs which are used as snares.Others do not spin webs but instead lie in wait for their prey or actively hunt. Webspinningspiders are more effective predators because their webs can continue tocatch prey after they have been abandoned. Spiders and harvestmen can be animportant component of bird diets.Spiders and mites (Arachnida)Money spiders(Linyphiidae) – over 270 species– Largest European family– Highly abundant, especially cereal crops– Small grey or black bodied spiders, 1.2–7.2 mm long– Hunting or web building– Drift through air on strands of silkWolf spiders (Lycosidae) – 36 species– Hunting spiders, mostly at ground level butoccasionally on low vegetation– Mostly brownish, but attractively marked andclothed in dense hairs, 3.5–18 mm long– Most abundant in field headlands– Good runners and can jump– Females conspicuous from May/June onwards withbrown or greenish-blue egg sacs© Jon OakleyAbove: Erigone sp.Below: Linyphiid sp.© Jon Oakley© Jon OakleyWolf spider(Pardosa sp.)StatusUnknown.How to encourageFor web-spinning species, vegetation or a soil surface with a diverse architectureprovide more opportunities to build webs. Leaving trash on a more cloddy surfacehelps retain spiders within fields in the autumn, while the presence of arableweeds provides a suitable structure in the spring and summer.Wolf spiders occur predominantly along field margins and penetrate less than 60metres into fields. Splitting fields using beetle banks or similar vegetative strips canhelp improve coverage within fields.Spiders are highly vulnerable to pyrethroid insecticides.Predatory mites (Phytoseiidae) – 34 species– Highly effective predators of spider mites due totheir voracity (20 spider mites per day), shortgeneration time (1 week) and high fecundity(40–60 eggs per female)– Some species are reared and released for biologicalcontrol– Also may feed on other small insects, honeydewand pollen, the latter boosting their reproductivecapability– More susceptible to insecticides than their spidermite prey© Koppert Biological SystemsAdult predatory mite(Phytoseiuluspersimilis)197Natural enemies: Spiders and mitesNatural enemies: Spiders and mites198

Further informationHGCA PublicationsAvailable at www.hgca.com/publicationsHGCA G51: Enhancing arable biodiversity through the management of uncroppedland: an HGCA guide (2011)Information from other organisationsFor guidance on IPM, habitat creation and biological control, seewww.gwct.org.uk/research/habitats/farmlandAcknowledgementsThis publication was funded by the three crop divisions of the Agriculture andHorticulture Development Board (HGCA, HDC and Potato Council). It waswritten by Dr Steve Ellis and Dr Sacha White, ADAS; Dr John Holland andDr Barbara Smith, Game and Wildlife Conservation Trust; and Dr RosemaryCollier and Andrew Jukes, Warwick Crop Centre. Additional information wasprovided by Becky Ward, PGRO; Dr Gillian Champion, BBRO; and CarolineNicholls, Dr Jon Knight and Chris Steele, Agriculture and HorticultureDevelopment Board.AHDB is grateful to many people who have commented on draft versions of thisencyclopaedia, including: Rosie Atwood, Sue Bleach, Anna Farrell, Dr VickyFoster, Fiona Geary and Jason Pole, Agriculture and Horticulture DevelopmentBoard; Dr Mark Stevens, BBRO; Dr Alan Dewar, Dewar Crop Protection Ltd;Dr Stephen Foster, Insecticide Resistance Action Group; Prof. Rod Blackshaw,University of Plymouth; John Humphreys and Keith Norman, HGCA Committeemembers.Edited by Dr Emily Boys, Agriculture and Horticulture Development Board.Photographs courtesy of ADAS, Ian Andrews, Stina Andersson (HIR Malmöhus),www.aphotofauna.com, Bayer CropScience, BBRO, Christoph Benisch, JoshuaBurnstone, Alan Dewar, Josef Dvorak, Fera, Emily Graham, Christine Hoepting,Ray Holden, John Holland, David Kerfoot, Roger Key, Paul Kitchener, KoppertBiological Solutions, Dan Leeder, J K Lindsey, Helen Martin, Robert McBride,Kevin McGee, Ian F G McLean, Jamie McMillan, Tony Morris, S Nygaard,Jon Oakley, PGRO, Frank Porch, T Ransom, S Rae, Rothamsted Research,G San Martin, Science & Advice for Scottish Agriculture (SASA), Syngenta, TheJames Hutton Institute, Peter Thompson, University of Warwick and Tom Will.While the Agriculture and Horticulture Development Board seeks to ensure that the informationcontained within this document is accurate at the time of printing, no warranty is given in respectthereof and, to the maximum extent permitted by law, the Agriculture and Horticulture DevelopmentBoard accepts no liability for loss, damage or injury howsoever caused (including that caused bynegligence) or suffered directly or indirectly in relation to information and opinions contained in oromitted from this document.Reference herein to trade names and proprietary products without stating that they are protecteddoes not imply that they may be regarded as unprotected and thus free for general use. Noendorsement of named products is intended, nor is any criticism implied of other alternative, butunnamed products.Autumn 2014© Agriculture and Horticulture Development Board 2014. All rights reserved.199Natural enemies

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