TOXICITY OF AVERMECTINS TO DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) POPULATIONS - IMPLICATIONS FOR SUSCEPTIBILITY MONITORING

The susceptibility of diamondback moth, Plutella xylostella (L.), larv ae to 2 avermectins, abamectin and MK-243 (4 ''-epi-methylamino-4 '' d eoxyavermectin B-1 hydrochloride), was assessed through toxicity evalu ations of 17-19 geographically diverse populations. Both avermectins w ere very potent to 3rd-instar diamondback moth; LC(50)s for abamectin and MK-243 ranged from 0.4 to 44.0 ng (AI)/ml and 0.2 to 8.0 np (AI)/m l, respectively. Although most populations showed resistance to methom yl and permethrin, the populations were not resistant to abamectin or MK-243. Pairwise correlations indicated lack of cross or multiple resi stance between the avermectins and methomyl and permethrin. This infor mation will serve as an aid for resistance monitoring programs and per mit comparative changes in susceptibility during commercial use. Such data are necessary to assist in decisions to recommend product use app ropriately in the context of resistance management.