Responses of Diadegma insulare (Hymenoptera : Ichneumonidae) to caterpillar feeding in a flight tunnel

A flight tunnel bioassay was used to evaluate attraction responses of femal e Diadegma insulare (Cresson), a host-specific parasitoid of the diamondbac k moth, Plutella xylostella (L.), to collard plants (Brassica oleracea var. acephala L.) infested with host and nonhost caterpillars. Adult female was ps showed increased responses to odors of the plant-host complex after a br ief contact experience with host-infested collard leaves. Such an increase shows evidence of associative learning in this parasitoid to the odor relea sed from the larval-plant complex. The same experimental design was also us ed to determine responses of the parasitoid to plants infested with nonhost larvae-cabbage looper, Trichoplusia ni (Hubner), and imported cabbageworm, Pieris rapae (L.). The female wasps conditioned to the plants infested wit h host larvae also showed increased responses to plants infested with larva e of cabbage looper or imported cabbageworm. These results indicate that pl ants damaged by host and nonhost caterpillars may release general odors tha t are attractive to D. insulare. The general damage odors caused by host an d nonhost larval feeding may enhance biological control of the diamondback moth. Host-search ability of the parasitoid increases after experiencing ho st damage. When host populations are low in fields, plant odors caused by g eneralist herbivore feeding may also attract D. insulare parasitoids to the vicinity, thereby improving encounter chances of the parasitoid encounteri ng diamondback moth larvae.