Innate responses of the parasitoids Cotesia glomerata and C. rubecula (Hymenoptera: Braconidae) to volatiles from different plant-herbivore complexes.

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.