Orientation of the parasitic wasp, Cotesia vestalis (Haliday) (Hymenoptera: Braconidae), to visual and olfactory cues of field mustard flowers, Brassica rapa L. (Brassicaceae), to exploit food sources

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Cotesia vestalis is a solitary endoparasitoid that attacks the larvae of the diamondback moth, Plutella xylostella, one of the most important pests of cruciferous crops. Since the female parasitoids do not exhibit host-feeding behavior, successful feeding on other items enhances the efficacy of the parasitoids as a biological control agent in agro-ecosystems, where sufficient amounts of food sources may not be available; however, there is little information on how they find and exploit food sources. Under laboratory conditions, we demonstrated that C. vestalis females lived significantly longer on Brassica rapa flowers than on water alone. In a dual-choice test, starved C. vestalis showed a significant preference for an inflorescence over an inflorescence stem with flowers removed. When the inflorescence and the stem were covered by clear bags to block only olfactory information, parasitoids preferred the inflorescence to the stem. Even when both were covered by brown porous bags to shut out only visual information, parasitoids preferred the inflorescence; however, non-starved parasitoids showed no significant preference between any tested sets. These results indicate that parasitoids orientate to flowers using visual and olfactory cues, respectively, depending on their own dietary state.