POPULATION-DYNAMICS OF WOOLLY APPLE APHID (HOMOPTERA, APHIDIDAE) IN WEST-VIRGINIA APPLE ORCHARDS

Woolly apple aphid, Eriosoma lanigerum (Hausmann), populations were st udied in eastern West Virginia from 1985 to 1989. In an unsprayed orch ard, peak abundance of arboreal populations was 22-24 colonies per tre e in early June each year. Spraying the orchard with a pyrethroid thre e times during 1989 had little effect on the population behavior, demo nstrating the resilence of the woolly apple aphid and its natural enem y guild. Nearly 20% of the aphid colonies in June had syrphid larvae p resent and parasitism by Aphelinus mali (Haldeman) was >50% in July. A ge structure of arboreal woolly apple aphid colonies varied through th e summer with a significant reduction in first instars in July, signal ling a return of aphids to the edaphic from the arboreal environment a t the time. Samples of arboreal populations were not useful for predic ting year-to-year population abundance or the extent of root infestati ons in a managed orchard. Microhabitat preference of arboreal colonies during the spring was for wound sites and other protected feeding sit es on the tree branches and trunk. Leaf axils were the predominant mic rohabitat (51% of the colonies observed) from the end of May through A ugust. Cicada oviposition sites were also highly preferred, with one o rchard having 98% of the colonies in cicada oviposition scars. Woolly apple aphid colonies were observed more often in wounds and protected sites on branches in sprayed orchards and in high density populations than in unsprayed or low density populations. We suggest that these pr otected sites act as refugia for woolly apple aphid populations in app le orchards.