Schlechtendalia chinensis

Lifecycle, Identification & Distribution

Fundatrices of Schlechtendalia chinensis induce horned galls on the Chinese sumac, Rhus chinensis. The galls are greenish-yellow or reddish green, densely covered with short, fine hairs, ovoid, becoming woody and irregular in shape with horn-like protrusions, from 1-6 cm long (see picture below). After several generations in the gall, emigrant alatae are produced in October and fly to found overwintering colonies on their secondary host, mosses such as Mnium and Plagiomnium.

Image above copyright Onidiras under a Creative Commons License.

Schlechtendalia chinensis aphids of all stages (except the newly hatched fundatrix) possess wax glands. The 56 wax gland plates are arranged in six parallel lines: two dorsal, two dorsolateral and two lateral. There are no wax glands on the dorsum of the newly hatched first instar fundatrix, but they do appear once the fundatrix enters its second instar (see Wei et al., 2020). The most heavily waxed individuals are those living inside the gall. The wax coating has several functions: it protects the aphids from predators and pathogens, and also from honeydew contamination resulting from the large number of aphids in the gall. The reason the first instar fundatrices lack wax is presumably twofold: firstly it reduces the energy investment needed by the non-feeding sexuales which produce the eggs from which fundatrices subsequently hatch; and secondly being waxless may improve mobility when the free-living first instar nymphs climb their tree to get to the young growth.

The emigrant alatae (not pictured) can be readily identified. The antennae are 5-segmented. The antennal terminal process is short and thick, much less than 0.5 times the length of the base of the last antennal segment. Antennal segment III is longer than the base of antennal segment V (cf. Schlechtendalia peitan, which has antennal segment III shorter than the base of antennal segment V). The antennae bear strap-like, annular secondary rhinaria. Antennal segments II-V each have at least partial separation of the sensoriated surface into smaller units. The pterostigma of the forewing extends in a curve around the tip of the wing. There are no siphunculi. The body length of emigrant Schlechtendalia chinensis alatae is about 1.5 mm.

For more pictures of the galls, and of the aphids inside the gall, see here.

Schlechtendalia chinensis is heteroecious (=host alternating) holocyclic, with an unusual one-year cycle. In early spring, aphid nymphs on the secondary host, mosses, develop into alate spring migrants, which are sexuparae. These sexuparae migrate to nearby primary hosts, Rhus chinensis trees, where they produce nonfeeding sexuales (=male and sexual female offspring) in the bark crevices. After mating, each female lives for about 3 weeks and then produces a single fundatrix ovoviviparously. The young fundatrix crawls up the trunk to feed on the new leaves, where it initiates gall formation. The fundatrix feeds inside the gall and produces numerous offspring. After several generations in the gall, winged migrants are produced in autumn which fly to mosses, their overwintering host. It is assumed all of their nymphs mature to sexuparae in the next spring (no wingless adults have been recorded on moss) and these spring migrants return to the primary host and begin a new cycle. The galls that Schlechtendalia chinensis produces on the primary host, known as Chinese gall-nuts, have been collected for many years. They have been used in tanning leather, in the preparation of dyes and for medicinal purposes. The species is found in China, Japan, Korea, Taiwan and Malaysia.

Other aphids on the same host

Primary host

Schlechtendalia chinensis has been recorded on 3 Sumac species (Rhus chinensis, Rhus japonica, Rhus punjabensis var. sinica).

• Blackman & Eastop list 11 species of aphid as feeding on Chinese Sumac (Rhus chinensis) worldwide, and provide formal identification keys (Show World list). Of those aphid species, Baker (2015) lists 2 as occurring in Britain (Show British list).

Secondary hosts

Schlechtendalia chinensis has been recorded from several species of moss.

• Its sexuparae have been recorded from 3 Mnium species (Mnium cuspidatum, Mnium maximoviczii, Mnium vesicatum). The only other aphids recorded on Mnium spp. are Muscaphis escherichi and Pseudacaudella rubida.

• It is the only species of aphid recorded from Plagiomnium maximoviczii (albeit that record is unconfirmed) but Jacksonia papillata, Muscaphis escherichi, & Muscaphis musci have been recorded from other Plagiomnium species.

• Blackman & Eastop list at least 16 species of aphid as feeding on mosses worldwide, and provide formal identification keys, but their is likely to be incomplete since Nurudea species, plus others in the genera listed, probably use mosses as secondary hosts. (Show World list). Of those aphid species, Baker (2015) lists 9 as occurring in Britain (Show British list).

Acknowledgements We are grateful to Onidiras for making his image of a Schlechtendalia chinensis gall available for use under a creative commons licence. We have used the account given by Wei et al. (2020) together with information from Roger Blackman & Victor Eastop in Aphids on Worlds Plants. We fully acknowledge these authors and those listed in the reference sections as the source for the (summarized) taxonomic information we have presented. Any errors in information are ours alone, and we would be very grateful for any corrections. For assistance on the terms used for aphid morphology we suggest the figure provided by Blackman & Eastop (2006).

Useful weblinks

References Wei, H. et al. (2020). Wax glands of the horned gall aphid, Schlechtendalia chinensis, at different stages. Arthropod Structure & Development 58 : 100976 Full text