Genetics and mechanisms of imidacloprid resistance in house flies

Three imidacloprid selections of a strain originally collected from Florida increased the level of resistance, ultimately resulting in a strain that had 2300-fold resistance in females and 130-fold in males. Imidacloprid resistance was not overcome with piperonyl butoxide (PBO) suggesting that resistance is not due to detoxification by cytochrome P450s. Resistance was mapped to autosomes 3 and 4. There was ⩾100-fold cross-resistance to acetamiprid and dinotefuran, but no cross-resistance to spinosad. The resistance in this imidacloprid selected population was unstable and declined over a period of several months. The significance of these results to management of imidacloprid resistance in the field, and potential mechanisms of resistance involved, are discussed.