PARASITISM OF DIAMONDBACK MOTH (LEPIDOPTERA:PLUTELLIDAE) LARVAE BY COTESIA PLUTELLAE (HYMENOPTERA: BRACONIDAE) AND DIADEGMA INSULARE (HYMENOPTERA: ICHNEUMONIDAE) IN CABBAGE FIELDS AFTER INUNDATIVE RELEASES OF C. PLUTELLAE

Authors: Mitchell, Everett; HU, GUANGYE - UNIV OF FL, GAINESVILLE; OKINE, JAMES - UNIV OF FL, GAINESVILLE; Carpenter, James

Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The diamondback moth is the most destructive pest of cabbage and other cruciferous crops worldwide. The annual cost of control, mostly with pesticides, is estimated at $1 billion. The problem is compounded by the fact that diamondback moth has become resistant to most synthetic pesticides. Scientists at the Center for Medical, Agricultural and Veterinary Entomology are developing alternative, environmentally-friendly tactics to control diamondback moth in Florida cabbage including the use of native and exotic parasitic wasps. Cotesia plutellae, an exotic parasitoid originally from southeast Asia, was released in cabbage fields in northeast Florida at the rate of 1200 total per acre over the growing season. The wasps parasitized 37% of diamondback larvae in the release and adjacent cabbage fields. Cotesia wasps also spread as far as 0.93 mi from the release area during the season. Results of these trials suggest that inundatory release of C. plutellae in the numbers used here probably will not result in economic control of diamondback moth. Moreover, the cost (÷$60 ac) of releasing this number of parasitoids is prohibitive. However, if release of fewer Cotesia/ac per season yield significant levels of parasitism of diamondback larvae, then it would be feasible to combine Cotesia releases with other control tactics such as pheromone for mating disruption, trap crops, preservation of the naturally occurring parasitic wasp Diadegma insulare, and Bt pesticides. Such a combination would provide a highly desirable integrated system for managing diamondback moth in cabbage.

Technical Abstract: Cocoons of Cotesia plutellae Kurdjumov were released for nine consecutive weeks along the margins of two commercial cabbage fields near Bunnell, Flagler Co., FL in spring 1996. The parasitism of diamondback moth [Plutella xylostella (L.)] larvae by C. plutellae and by the native parasitoid Diadegma insulare (Cresson) was evaluated in release and nearby fields using two methods - sentinel collard or cabbage plants and routine sampling. Total parasitism of diamondback moth larvae on sentinel plants in the release and adjacent fields was 35.7%. There were no significant differences in the level of parasitism by C. plutellae among sentinel plant locations within the release fields. In non-release fields, the parasitoids spread as far as 1,500 m from the release area during the release period, but parasitism of larvae on sentinel plants decreased as the distance from the release area increased. Parasitism of diamondback moth larvae by D. insulare was 8.3% in Cotesia release and adjacent fields, but 14.6% in the nearby fields. Routine sampling of cabbage for diamondback moth larvae demonstrated a total of 37.4% larval parasitism by C. plutellae in the release and adjacent fields, which is similar to that recorded on sentinel plants. However, C. plutellae were detected only as far as 800 m from the release area in routine sampling of cabbage, and total parasitism in the spread fields also was very low. D. insulare contributed only 1.1% parasitism of the larvae that were routinely sampled from all the fields. The results demonstrated that C. plutellae was more effective in attacking diamondback moth larvae than D. insulare in this study when the field populations of diamondback moths were low.