The influence of plant species on attraction and host acceptance in Cotesia glomerata (Hymenoptera:Braconidae)

Females of the larval parasitoid Cotesia glomerata (L.) use plant-associated cues to locate their lepidopteran host, Pieris rapae L. In this study we investigated the influence of four-host plant species, Brassica oleracea var. acephala ('Vates' kale), Tropaeolum majus (nasturtium), Lunaria annua (honesty), and Cleome spinosa (spider flower), on two components of the host selection process in C. glomerata, namely, attraction and host acceptance. Choice tests in a flight tunnel showed that parasitoids were attracted to some host plant species more than to others in the absence of host larvae. B. oleracea was the most attractive plant species, followed by L. annua, T. majus, and C. spinosa. In previous studies it was shown that B. oleracea carries highly suitable hosts for C. glomerata and that, in the field, parasitization rates on this plant were the highest. When host larvae were reared on the four host plant species and then transferred to a common substrate (B. oleracea var. capitata, cabbage), plant species that had sewed as diet for the hosts did not have a significant effect on acceptance for parasitization. Thus, parasitoids were attracted to host plant species differentially, but they did not discriminate among host larvae based on the dietary history of their hosts. For C. glomerata, it appears that phytochemistry mediates host selection more by influencing parasitoid attraction than it does by affecting host acceptance.