Introduction: The house fly, Musca domestica L., is known as one of the most important hygiene problems worldwide. It has shown a high potential to develop resistance to chemical insecticides. This study was undertaken to determine the susceptibility or resistance of the house fly, which were collected from 3 livestock farms near the city of Ahvaz, to prevalent pyrethroid insecticides (delthamethrin, lambda-cyhalothrin, cypermethrin).
Methods and Materials: Females of 3 field strains, Molasani, Saiahi and Shoeibi, and one susceptible population, were exposed to each insecticide with two bioassay methods: topical and residual methods.
Results: All three populations developed resistance to the prevalent pyrethroid insecticides. This phenomenon was determined by both topical and residual methods. The highest resistance level to delthamethrin insecticide was observed in the Molasani population with a resistance factor of RF>500 determined by both bioassay methods. The Siahi population showed the highest level of resistance to both the lambda-cyhalothrin and cypermethrin insecticides. Resistance factor values of this population to the above-named insecticides recorded by both bioassay methods were RF>1000 and RF>450, respectively. The highest resistance level of all was observed in the Siahi strain to cypermethrin.
Conclusions: Continuous use of insecticides with the same modes of action results in the development of class- or cross-resistance in target pests. Rotational use of insecticides with different modes of action could lead to the destruction of the resistant population and reduce the development of resistance in the house fly population of these places.