Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/1998
Publication Date: N/A
Interpretive Summary: Diamondback moth (DBM) ranks high among the most destructive insect pests of cruciferous crops worldwide costing growers an estimated $1 billion dollars annually in crop losses and pest control. The struggle to manage this pest long has relied upon multiple applications of pesticides each growing season which has resulted in a very high incidence of resistance to omost insecticides including biologicals such as Bacillus thuringensis (Bt) Scientists at the Center for Medical, Agricultural, and Veterinary Entomology at Gainesville, Florida, are developing an integrated management program for DBM in Florida cabbage using a combination of tactics including pheromones, natural enemies, and biological pesticides such as Bt. One approach is to supplement the naturally occurring populations of DBM larval parasitoids, primarily Diadegma insulare, with timely releases of native and exotic parasitoids raised outdoors in field nursery cages strategically yplaced in and around cabbage fields. Two species of parasitoid, Cotesia plutellae and D. insulare, were reared outdoors in field cages from November 1996 to February 1997 to determine the feasibility of using this technique to supplement naturally-developing populations of D. insulare. Cotesia plutellae is an exotic species that has been shown to have some effect on DBM populations, but it does not survive year round in Florida. Both species attacked DBM larvae during winter, completed development in the host, and increased in numbers in field cages. Colonizing these two species in field cages would provide a good source for large numbers of C. plutellae and D. insulare to control DBM in cabbage. The procedure can be easily adopted by growers of commercial cabbage as the rearing facilities were inexpensive and required little labor input.
Technical Abstract: Two species of parasitoids, Cotesia plutellae (Hymenoptera: Braconidae) and Diadegma insulare (Hymenoptera: Ichneumonidae), of diamondback moth, Plutella xylostella, (Lepidoptera: Plutellidae), were colonized in cages in cabbage fields west of Bunnell, Florida, from November 1996 to February 1997. Two kinds of cages were used: large-screened cages and screened laundry hampers. Both parasitoids attacked their host during the winter, completed development within the host, and increased in numbers within field cages. Parasitism of diamondback moth larvae by C. plutellae was 36- 42% in laundry hampers, and 35-65% in large screened cages. The sex ratio of the emerging C. plutellae was 1:1-1.2 (female:male) in laundry hampers and 1:0.8-1.3 in large screened cages. Parasitism of diamondback moth larvae by D. insulare was 55-90%, parasitoid adults emerged from 89% of the cocoons, and the sex ratio was 1:1.4-2.1 (female:male) in large screened cages. The results showed that it is possible to rear these parasitoids in field nursery cages to provide parasitoid sources for release to control diamondback moth in cabbage in Florida.