BEHAVIORAL-RESPONSES TO HOST FOODPLANTS OF 2 POPULATIONS OF THE INSECT PARASITOID COTESIA-CONGREGATA (SAY)

To test the hypothesis that natural enemy populations differ in their behavioral responses to plants or to plant allelochemicals, we compare d two populations of the gregarious larval endoparasitoid, Cotesia con gregata (Say) (Hymenoptera: Braconidae) that differed in their histori cal and present exposure to tobacco. The major hosts for both populati ons were Manduca sexta L. and M. quinquemaculata (Haworth) (Lepidopter a: Sphingidae), but these hosts were typically encountered on tobacco by parasitoids in one population (Upper Marlboro) and on tomato by par asitoids in another population (Wye). Early in the season, Wye parasit oids preferred to oviposit in M. sexta on tomato rather than on tobacc o and Upper Marlboro parasitoids showed no preference; neither populat ion showed any preference later in the season. Neither of the strains originating from the two populations showed a landing preference for t obacco or tomato in flight chamber trials, but Upper Marlboro parasito ids searched longer on tobacco than on tomato, and Wye parasitoids sea rched longer on tomato. When nicotine solutions were applied to tobacc o leaf, searching re sponses of Upper Marlboro parasitoids were enhanc ed by 0.001-1.0% nicotine, and searching responses of Wye parasitoids were decreased by 0.01-1.0% nicotine. We speculate that population dif ferences in searching responses to tobacco and nicotine may explain th e differential parasitism responses found early in the season.