Cross-resistance, stability, and fitness cost of resistance to imidacloprid in Musca domestica L., (Diptera: Muscidae).

Imidacloprid, a neonicotinoid insecticide, has been used frequently for the management of Musca domestica L., (Diptera: Muscidae) worldwide. To design the strategy for resistance management, life history traits were established for imidacloprid-resistant, susceptible counterpart, and reciprocal crosses M. domestica strains based on laboratory observations. Bioassay results showed that the imidacloprid-selected strain developed a resistance ratio of 106-fold to imidacloprid, 19-fold to nitenpyram, 29-fold to chlorpyrifos, and 3.8-fold to cypermethrin compared to that of the susceptible counterpart strain. The imidacloprid-selected strain showed very low cross-resistance against nitenpyram and cypermethrin and a lack of cross-resistance to chlorpyrifos. Resistance to imidacloprid, nitenpyram, and chlorpyrifos was unstable, while resistance to cypermethrin was stable in Imida-SEL strain of M. domestica. The imidacloprid-selected strain had a relative fitness of 0.61 and lower fecundity, hatchability, number of next-generation larvae, and net reproductive rate compared with the susceptible counterpart strain. Mean population growth rates, such as intrinsic rate of population increase and biotic potential, were lower for the imidacloprid-selected strain compared with the susceptible counterpart strain. Development of resistance can cost considerable fitness for the imidacloprid-selected strain. The present study provided useful information for making potential management strategies to overcome development of resistance.