Submitted to: Florida Entomologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/21/1997
Publication Date: N/A
Citation: Interpretive Summary: The diamondback moth (DBM) is the most serious pest of cruciferous crops worldwide. In Florida, DBM has become such a serious pest that many growers have abandoned cabbage production in favor of sometimes less profitable crops. Scientists at the Insect Attractants, Behavior, and Basic Biology Research Laboratory, Gainesville, FL, are investigating ways to manage DBM with less reliance upon conventional pesticides. Cotesia plutellae, an exotic parasitic wasp of DBM larvae, was systematically released for several weeks during spring of 1993 and 1994 at rates of 200 to 600 per ac in cabbage fields ranging in size from 20-30 ac. C. plutellae wasps only sting very small larvae and once parasitized they cease feeding. Parasitism by C. plutellae ranged from 5-15% and generally was related to numbers release per ac and the frequency and kind of pesticides applied. Diadegma insulare, a naturally-occurring parasitic wasp of DBM, was even more effective than C. plutellae often destroying >50% of the larvae. The 2 parasite species are complimentary and can be used together in IPM programs. However, C. plutellae does not survive year round in Florida and must be reintroduced each growing season. Recent research showed planting collards in and around cabbage fields lured a significant number of DBM adults away from the cabbage. Supplemental releases of C. plutellae in the collard plantings would allow this parasite to build its numbers along with D. insulare, and both species could spread into the cabbage to attack DBM larvae. This approach could greatly reduce grower costs as fewer C. plutellae parasites would need to be released, and the number and frequency of pesticide applications also would be reduced. This strategy also would provide less opportunity for DBM to develop resistance to pesticides.
Technical Abstract: Cotesia plutellae Kurdjumov was evaluated as a potential biological control agent for diamondback moth (DBM), Plutella xylostella (Linnaeus), in cabbage in spring 1993 and 1994. The parasitoids were reared in a commercial insectary in Texas, delivered overnight via air express, and released almost immediately in cabbage fields in north central Florida. In 1993, only adult parasitoids were released, but adults and cocoons were released in 1994. The numbers of C. plutellae released ranged from 456/ha/wk in 1993 to 1,334/ha/wk in 1994; four consecutive releases were made each year beginning in early February. Parasitism of DBM larvae by C. plutellae ranged from 6.6 to 15.0%, and the level of parasitism was related to the total numbers of parasitoids released. C. plutellae parasitoids were complimentary to the naturally occurring parasitoid Diadegma insulare (Cresson), and the combined mean seasonal parasitism of DBM exceeded 35% in some fields. There was no evidence that C. plutellae became established in the general area although >124,000 parasitoids were released over the 2-year test period. Therefore, for C. plutellae to have a significant impact on control of DBM in cabbage the parasitoid must be released at regular intervals and in sufficient numbers each growing season.