Because of the potentially serious damage rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), can cause to apple fruit and branch development, prophylactic insecticides are often used for control. If biological control could be relied on, the amount of pesticide applied in orchards could be reduced. This study examined biological control of rosy apple aphid in eastern West Virginia and the potential for enhancement through conservation biological control, in particular, the effect of interplanting extrafloral nectar-bearing peach trees. By 20 d after first bloom, only 2% of fundatrices initially present survived to form colonies based on regression of data from 687 colonies. Exclusion studies showed that many of the early colonies were probably destroyed by predation; the major predator responsible seemed to be adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Mortality before apple bloom was most important in controlling rosy apple aphid population growth but by itself is not sufficiently reliable to prevent economic injury. Interplanting of extrafloral nectar-bearing trees did not increase biological control, and interplanting with 50% trees with extrafloral nectar glands reduced biological control. The number of leaf curl colonies in the 50% interplanted orchards was lower than in monoculture orchards, suggesting a preference of alate oviparae for more diverse habitats, supporting the resource concentration hypothesis but not at a level sufficient to prevent injury. Predation and parasitism after the formation of leaf curl colonies was not adequate to control rosy apple aphid populations.
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