Feeding and egg distribution studies of Heringia calcarata (Diptera: Syrphidae), a specialized predator of woolly apple aphid (Homoptera: Eriosomatidae) in Virginia apple orchards.

Predation by the aphidophagous syrphid fly Heringia calcarata (Loew) on woolly apple aphid, Eriosoma lanigerum (Hausmann), was studied in the laboratory and in Virginia apple orchards. Feeding studies compared the prey suitability of three temporally sympatric aphid pests of apple: spirea aphid, Aphis spiraecola Patch; rosy apple aphid, Dysaphis plantaginea (Passerini); and woolly apple aphid. Significantly more H. calcarata larvae survived and completed development on a pure diet of woolly apple aphid than on rosy apple aphid, and none survived on spirea aphid. Final larval weights were significantly greater, and the larval developmental period was significantly shorter on woolly apple aphid than on rosy apple aphid, but neither the duration of pupal development nor adult weight differed between diets. H. calcarata larvae consumed an average of 105 woolly apple aphids during their development. Naïve, neonate larvae given access to all possible pair combinations of woolly apple aphid, rosy apple aphid, and spirea aphid consumed significantly more woolly apple aphids in all pairings that included woolly apple aphid. When given a choice of rosy apple aphid and spirea aphid, significantly more rosy apple aphids were consumed. Weekly counts of syrphid eggs found in woolly apple aphid, rosy apple aphid, and spirea aphid colonies collected from apple trees showed that two generalist hover fly predators, Eupeodes americanus (Wiedemann) and Syrphus rectus Osten Sacken, were present in colonies of all three aphid species and that E. americanus was the most abundant syrphid predator in A. spiraecola and D. plantaginea colonies. H. calcarata eggs were found only in woolly apple aphid colonies and were more abundant there than E. americanus and S. rectus. These data suggest that H. calcarata is a specialized predator of woolly apple aphid in the apple ecosystem in Virginia.