SUPPRESSION OF DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) WITH AN ENTOMOPATHOGENIC NEMATODE (RHABDITIDA, STEINERNEMATIDAE) AND BACILLUS-THURINGIENSIS BERLINER

We tested the efficacy of the All strain of Steinernema carpocapsae (W eiser) against larvae of the diamondback moth, Plutella xylostella (L. ). In laboratory bioassays we found that (1) commercially formulated n ematodes produced in vitro were as effective as nematodes produced in vivo, (2) resistance of P. xylostella to Bacillus thuringiensis Berlin er subsp, kurstaki did not confer cross-resistance to nematodes, (3) m ortality caused by nematodes was higher for early than late 3rd-instar P. xylostella larvae, and (4) no interaction occurred when B. thuring iensis and nematodes were combined against a susceptible strain of P, xylostella, but an antagonistic interaction occurred between the 2 pat hogens against a strain of P. xylostella resistant to B. thuringiensis . In field trials conducted on 2 watercress [Rorippa Nasturtium-aquati cum (L.) Hayek] farms in Hawaii, nematodes provided 41% control, B. th uringiensis subsp. aizawai gave 44% control, and the combined treatmen t (B. thuringiensis plus nematodes both at half rate) resulted in 58% control. Using nemodes to control diamondback moth can theoretically r educe resistance development in diamondback moth populations to B. thu ringiensis products, but repeated applications of nematodes will proba bly be ineffective in attaining control (suggested in simulation model ). The results of this study demonstrate that nematodes may be a usefu l component of integrated pest management programs if efficacy can Le increased, especially for populations of P, xylostella that are resist ant to B. thuringiensis.