LEARNING TO DISCRIMINATE BETWEEN INFOCHEMICALS FROM DIFFERENT PLANT-HOST COMPLEXES BY THE PARASITOIDS COTESIA-GLOMERATA AND COTESIA-RUBECULA

Comparison of closely related species can elucidate adaptive differenc es in species characteristics. The present study compares the effect o f experience on the host-finding behaviour of two Cotesia (Hymenoptera : Braconidae) parasitoid species that differ in their degree of specia lization. After multiple experiences with host larvae, females of the generalist parasitoid Cotesia glomerata showed a clear preference for volatiles from Pieris brassicae-infested Brussels sprouts leaves over P. rapae-infested Brussels sprouts leaves in two-choice tests ('prefer ence learning at herbivore level?). A single experience with a host di d not lead to such preferences. Experience of adult C. glomerata with different P. brassicae-infested cabbage varieties or nasturtium (Tropa eolum majus L.) led to preferences for the experienced plant-host comp lex in most cases ('preference learning at plant level'). No effect of rearing plant (early adult learning) on plant preference was found. I n contrast to the,generalist C. glomerata, females of the specialist C . rubecula did not show preference learning at the herbivore level. At the plant level, experience with different P. rapae-infested cabbage varieties in no case resulted in a difference in preference between tr eatments. The results support the hypothesis that learning plays a mor e important role in searching in generalists than in specialist parasi toids. The behaviour of the generalist C. glomerata nta was more easil y changed by experience than that of the specialist C. rubecula.