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To determine and compare innate preferences of the parasitoid species Cotesia glomerata and C. rubecula for different plant-herbivore complexes, long-range (1-m) foraging behavior was studied in dual-choice experiments in a wind tunnel. In this study we tested the hypothesis that naive females of the specialist C. rubecula should show more pronounced preferences for different plant-herbivore complexes than females of the generalist C. glomerata. The herbivore species used were the pierids Pieris brassicae, P. rapae, P. Napi, and Aporia crataegi and the nonhosts Plutella xylostella and Mamestra brassicae. All herbivore species feed mainly on cabbage arid wild crucifers, except Aporia crataegi, which feeds on species of Rosaceae. Both parasitoid species preferred herbivore-damaged plants over nondamaged plants. Neither C. rubecula nor C. glomerata discriminated between plants infested by different caterpillar species, not even between plants infested by host- and nonhost species. Both parasitoid species showed preferences for certain cabbage cultivars and plant species. No differences were found in innate host-searching behavior between C. glomerata and C. rubecula. The tritrophic system cabbage-caterpillars-Cotesia sp. seems to lack specificity on the herbivore level, whereas on the plant level differences in attractiveness to parasitoids were found.

Comparison of closely related species can elucidate adaptive differences in species characteristics. The present study compares the effect of experience on the host-finding behaviour of two Cotesia (Hymenoptera: Braconidae) parasitoid species that differ in their degree of specialization. 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 (preference learning at herbivore level). A single experience with a host did not lead to such preferences. Experience of adult C. glomerata with different P. brassicae-infested cabbage varieties or nasturtium (Tropaeolum majus L.) led to preferences for the experienced plant-host complex in most cases (preference learning at plant level). No effect of rearing plant (early adult learning) on plant preference was found. In 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 treatments. The results support the hypothesis that learning plays a more important role in searching in generalists than in specialist parasitoids. The behaviour of the generalist C. glomerata was more easily changed by experience than that of the specialist C. rubecula.

To determine and compare innate preferences of the parasitoid species Cotesia glomerata and C. rubecula for different plant-herbivore complexes, long-range (1-m) foraging behavior was studied in dual-choice experiments in a wind tunnel. In this study we tested the hypothesis that naive females of the specialist C. rubecula should show more pronounced preferences for different plant-herbivore complexes than females of the generalist C. glomerata. The herbivore species used were the pierids Pieris brassicae, P. rapae, P. Napi, and Aporia crataegi and the nonhosts Plutella xylostella and Mamestra brassicae. All herbivore species feed mainly on cabbage arid wild crucifers, except Aporia crataegi, which feeds on species of Rosaceae. Both parasitoid species preferred herbivore-damaged plants over nondamaged plants. Neither C. rubecula nor C. glomerata discriminated between plants infested by different caterpillar species, not even between plants infested by host- and nonhost species. Both parasitoid species showed preferences for certain cabbage cultivars and plant species. No differences were found in innate host-searching behavior between C. glomerata and C. rubecula. The tritrophic system cabbage-caterpillars-Cotesia sp. seems to lack specificity on the herbivore level, whereas on the plant level differences in attractiveness to parasitoids were found.