Field evaluations of the contribution of predators and the parasitoid, Aphelinus mali, to biological control of woolly apple aphid, Eriosoma lanigerum, in Virginia, USA

Abstract

A series of experiments in Virginia, USA apple orchards evaluated the temporal effects of natural enemies on Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) colonies on potted and mature apple trees. Exclusion cage studies using potted trees resulted in increasing colony numbers on fully caged trees and declining colony numbers or colony extinction on trees exposed to natural enemies. Closer examination of the fate of individual colonies on potted trees produced a similar result and revealed that syrphids oviposited in colonies within two days of tree deployment. Heringia calcarata (Loew) (Diptera: Syrphidae) was the predominant predator and had a greater and more rapid impact on colonies than did the parasitoid Aphelinus mali (Haldeman) (Hymenoptera: Aphelinidae). The fate of cohorts of naturally-occurring E. lanigerum colonies on mature trees was examined over two seasons and confirmed that H. calcarata and A. mali were most strongly associated with colony demise.