Adulticidal Activity of the Insect Growth Regulators Methoprene and Cyromazine in House Flies (Musca domestica L.): Evidence from Feeding Trials

House flies (<i>Musca domestica</i> L.) are major vectors of numerous pathogens affecting both humans and animals. The global distribution of house flies has been steadily increasing the expansion of human settlements, increased waste production, and the growth of livestock farms established to meet the demand for animal-derived products. Frequent exposure to intensive pesticide applications in agricultural and livestock areas has accelerated the development of insecticide resistance, posing a serious challenge to sustainable control efforts. The widespread and repeated use of conventional chemical insecticides has contributed to rapid resistance evolution in many populations worldwide. In this study, the acute toxic effects of two insect growth regulators (IGRs)-cyromazine and methoprene-commonly used in the larval stages of house flies were evaluated against adult flies. Treatments were applied (3 replicates) orally via 40% sugar-water solutions containing 1%, 5%, and 10% concentrations, and bioassays were conducted on eight distinct house fly populations. The results showed that cyromazine caused average adult mortalities of 76.35%, 81.00%, and 84.50% within 48 h, while methoprene produced 70.62%, 99.37%, and 100% mortality at the same concentrations. At 10%, methoprene achieved 100% mortality across all populations, whereas cyromazine induced mortality ranging from 44.28% to 100%. These findings suggest that IGRs can be effective alternatives to conventional insecticides and can be integrated into IPM/IVM programs to reduce chemical use and delay resistance.