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

A flight tunnel bioassay was used to evaluate attraction responses of female Diadegma insulare (Cresson), a host-specific parasitoid of the diamondback moth, Plutella xylostella (L.), to collard plants (Brassica oleracea var. acephala L.) infested with host and nonhost caterpillars. Adult female wasps showed increased responses to odors of the plant-host complex after a brief contact experience with host-infested collard leaves. Such an increase shows evidence of associative learning in this parasitoid to the odor released from the larval-plant complex. The same experimental design was also used 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 with host larvae also showed increased responses to plants infested with larvae of cabbage looper or imported cabbageworm. These results indicate that plants damaged by host and nonhost caterpillars may release general odors that are attractive to D. insulare. The general damage odors caused by host and nonhost larval feeding may enhance biological control of the diamondback moth. Host-search ability of the parasitoid increases after experiencing host damage. When host populations are low in fields, plant odors caused by generalist herbivore feeding may also attract D. insulare parasitoids to the vicinity, thereby improving encounter chances of the parasitoid encountering diamondback moth larvae.