Submitted to: Journal of Insect Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/4/2001
Publication Date: N/A
Citation: Interpretive Summary: The diamondback moth (DBM) is the most important insect pest of cruciferous crops (e.g. cabbage, broccoli, and mustard) worldwide. It costs growers an estimated $1 billion annually in crop losses and pest control. Growers typically rely on pesticides to manage this pest. To deal with the problems associated with pesticide application, such as pesticide resistance, environmental pollution and increasing control cost, scientists at the Center for Medical, Agricultural and Veterinary Entomology at Gainesville, FL are developing an integrated pest management program for DBM in cabbage. The program includes pheromones, natural enemies, trap crops and bio-rational pesticides such as Bt. A parasitic wasp, Diadegma insulare, has been colonized and released into cabbage fields for biological control of DBM. To better understand using this parasite, behavioral studies were conducted in flight tunnels. Results showed that cabbage plants damaged by DBM larval feeding produced chemical cues that attracted Diadegma insulare to DBM larvae if the parasite previously was exposed to these cues. This associative learning behavior was used to enhance natural control of DBM in cabbage in spring 1998. After experiencing plants damaged by DBM larvae, the Diadegma parasites searched for their hosts more efficiently. The scientists also found that cabbage plants damaged by non-host caterpillar species, such as cabbage looper and imported cabbageworm, also emitted chemical cues that attracted experienced Diadegma. When DBM larval populations are very low in cabbage fields, damage caused by non-host caterpillars probably stimulate parasites to continue their search for DBM larval hosts. The result is that the parasites are retained in the field longer, resulting in longer, better control of DBM.
Technical Abstract: A flight tunnel bioassay was used to evaluate attraction responses of female Diadegma insulare (Cresson), a host-specific parasitoid of 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 used to compare responses of the parasitoid to plants infested with host larvae versus those infested with non-host larvae [cabbage looper, Trichoplusia ni (Hubner), and imported cabbageworm, Pieris rapae (L.)]. No significant differences in responses were shown to plants infested with larvae of diamondback moth, cabbage looper, or imported cabbageworm. These results indicate that plants damaged by host and non- host caterpillars may release common chemicals that are attractive to D. insulare. The plant odors caused by non-host larval feeding may facilitate host-finding by this parasitoid. When host populations are low in fields, plant odors caused by generalist herbivore feeding may attract D. insulare parasitoids to the vicinity, thereby improving encounter chances of the parasitoid with diamondback moth larvae.