Learning as a mechanism for local adaptation to plants in an insect parasitoid

Optimally, parasitoids should locate most quickly and make the greatest reproductive investment in hosts encountered on the parasitoid-host-natal plant yet retain flexibility to exploit hosts that may be present on alternative hostplants. To test this hypothesis, we quantified the effects of sequentially learned plant cues on searching responses and ovipositional decisions of the braconid wasp, Cotesia congregata (Say), a gregarious larval endoparasitoid of the solanaceous specialist, Manduca sexta L., and other specialized sphingids. Newly-emerged parasitoids received a postemergence experience (“early adult learning”) with M. sexta and tobacco or M. sexta and tomato, or with M. sexta and novel parsley or arugula, followed by ovipositional experience with the same or alternative plant. Parasitoids had no other contact with plants. Hosts were reared on a laboratory diet. Effects of the two learning experiences were additive and differed between host and novel plants. Experience with hostplants induced an increased searching response to the plant(s) experienced and the proportion of females allocated per brood but had no effect on clutch size. In contrast, experience with novel plants induced an increased searching response to the plant(s) experienced and mixed effects on clutch size but had no effect on sex ratios. Results demonstrate the role of both inherent and learned plant cues on ovipositional decisions, and suggest a mechanism for local adaptation to host/hostplants.