Cross-resistance to the biological insecticide abamectin in pyrethroid-resistant house flies

Cross-resistance to abamectin, a new, potent, and highly promising biological insecticide, was found in two pyrethroid-resistant strains of house fly. One strain was laboratory selected (LPR) and one was field collected (Dairy), having 25-fold and 5.9-fold cross-resistance to abamectin, respectively. Cross-resistance in the LPR strain was polygenic, associated with genes on chromosomes 2 and 3, and could be partially suppressed by the mixed-function oxidase inhibitor piperonyl butoxide. Based on genetic and toxicological data, the mechanisms associated with the pyrethroid-induced cross-resistance to abamectic appear to be MFO-mediated metabolism and decreased cuticular penetration.