PLANT NATURAL ENEMY ASSOCIATION IN THE TRITROPHIC SYSTEM, COTESIA-RUBECULA-PIERIS-RAPAE-BRASSICEAE (CRUCIFERAE) .1. SOURCES OF INFOCHEMICALS

The role of airborne infochemicals in host selection by the parasitoid Cotesia rubecula (Marshal) (Hymenoptera: Braconidae) was examined in a wind tunnel. To elucidate the role of volatile chemicals in attracting C. rubecula to cabbage infested by the host [Pieris rapae L. (Lepidoptera: Pieridae)], the potential sources of volatiles related to P. rapae infestation on cabbage were tested individually. The responses of females to nonhost plant species, bean and geranium, as well as to frass of a nonhost lepidopteran were also examined. C. rubecula was attracted to cabbage previously infested by P. rapae and to frass and regurgitate of P. rapae. No attraction was observed to larvae of P. rapae alone. Females were also attracted to mechanically damaged cabbage, cabbage previously infested by Plutella xylostella L. (Lepidoptera: Plutellidae) (a nonhost lepidopteran herbivore), and cabbage previously infested by snails (a nonhost, noninsect herbivore). Intact cabbage, bean, and geranium plants elicited no attraction. A low frequency of attraction was observed to mechanically damaged bean and geranium. Attraction was also observed to frass of P. xylostella. Volatiles from cabbage related to damage, and volatiles from frass and regurgitate of the host seem to play an important role in guiding C. rubecula to plants infested by its host.