Toxicity of avermectins to diamondback moth (Lepidoptera: Plutellidae) populations: implications for susceptibility monitoring

The susceptibility of diamondback moth, Plutella xylostella (L.), larvae to 2 avermectins, abamectin and MK-243 (4"-epi-methylamino-4" deoxyavermectin B1 hydrochloride), was assessed through toxicity evaluations of 17-19 geographically diverse populations. Both avermectins were very potent to 3rd-instar diamondback moth LC50s for abamectin and NIK-243 ranged from 0.4 to 44.0 ng (AI)/ml and 0.2 to 8.0 ng (AI)/ml, respectively. Although most populations showed resistance to methomyl and permethrin, the populations were not resistant to abamectin or MK-243. Pairwise correlations indicated lack of cross or multiple resistance between the avermectins and methomyl and permethrin. This information will serve as an aid for resistance monitoring programs and permit comparative changes in susceptibility during commercial use. Such data are necessary to assist in decisions to recommend product use appropriately in the context of resistance management