Why are these white stopper (Eugenia axillaris) fruits yellow and ribbed? It’s likely the handiwork of a gall midge. Not too much is known this tiny insect, long co-evolved with white stopper, that does not have a common name. Its scientific name is Dasineura eugeniae, and you can see how the species name references this intimate relationship.
“Normal” white stopper fruits are small round drupes (fruits with a single seed) that ripen from golden to reddish to blue-black …
This specialized gall midge deposits an egg in a ripening fruit, and the developing larva dramatically disfigures the fruit …
An adult gall midge will exit the fruit to repeat the cycle. You can see an exit hole in the photo above.
Most gall-makers are specific not only to a particular species of plant but to a particular part of the plant like the fruits, leaves, branches, stems, flowers, flower buds, or roots. Gallmakers include midges, aphids, scale insects, plant lice, special wasps, mites, fungus, and nematodes. Galls come in a variety of shapes and sizes.
This and other species of gall midges were trapped during routine mosquito surveillance efforts by the Keys Mosquito Control District. Key’s Research Entomologist Dr. Larry Hribar, a former post-doc at the Florida Medical Entomology Laboratory and former employee of the Indian River Mosquito Control District, described some of the gall midges he encountered in light trap collections in the Florida Scientist in a paper titled, Collection records for some gall midges from the Florida Keys (Diptera: Cecidomyiidae).
Another gall midge, Stephomyia eugeniae, that does not have a common name, is associated with the underside of the leaves of white stoppers, as its species name also reflects …
Often large populations will cluster on the underside of a leaf as seen above. Closer up each individual gall is boot -shaped and covered with white hairs. After pupating, a “new” gall midge emerges from the toe of the boot-shaped gall. Thanks to Will Jones (Class of 2008) for the photos below of Stephomyia eugeniae galls engulfing a white stopper leaf …
Enjoy the Oslo Riverfront Conservation Area 