BIOLOGICAL CONTROL Oviposition Response of Cotesia plutellae (Hymenoptera: Braconidae) to Sterile and Normal Diamondback Moth (Lepidoptera: Plutellidae) Larvae

Augmentative release of the endoparasitoid Cotesia plutellae (Kurdjumov) to control diamondback moth, Plutella xylostella (L.), in cabbage, Brassica oleracea variety capitata (L.), would be expensive for growers if done continually during a growing season. A method for establishing released parasitoids would be very beneficial in the control of this pest. One method under consideration is to use sterile diamondback moth larvae deposited on 'nursery' collard plants as hosts for C. plutellae to allow the parasitoid to build up in numbers and spread into adjacent cabbage fields. Therefore, the ability of C. plutellae to accept and develop successfully in normal and sterile diamondback larvae was evaluated. C. plutellae does not discriminate between normal larvae and larvae from parents sterilized by gamma radiation, and both sets of larvae served as suitable hosts for the parasitoid. Parasitism, foliage consumption, and survivorship were similar for the 2 types of larvae. Adult female Fl parasitoids developed from sterile diamondback larvae were as fit as those from normal larvae. In laboratory bioassays, sterile and normal diamondback larvae traversed similar distances before pupation. Field cage assays showed less distance traversed by both types of larvae compared with the laboratory studies. Survivorship for both types of larvae was very low under field conditions. Results indicate that sterile diamondback moth larvae are acceptable hosts for C. plutellae and suggest that the nursery approach toward establishment and build up of numbers would be a viable approach to in-field production of the parasitoid with little chance for harm to nearby cabbage because of spread of sterile larvae from the nursery plants. This approach could be a cost effective way to augment naturally occurring parasitoids and predators in diamondback moth management