This study evaluated the insect growth regulator pyriproxyfen (PPF) for its inhibitory effects on the adult emergence of fly (Musca domestica) and mosquito (Culex pipiens) larvae. Laboratory bioassays with a product containing 0.5% PPF were conducted using diet incorporation for fly larvae and water immersion for mosquito larvae at concentrations of 80, 160, and 320 mg/kg (flies) or mg/L (mosquitoes). PPF treatment reduced adult emergence in a dose-dependent manner. At 160 mg/kg (or mg/L), corrected adult emergence inhibition rates exceeded 80%, which meets regulatory thresholds for efficacy. Residual activity tests demonstrated sustained effects, with fly larvae showing 70% inhibition and mosquito larvae complete suppression (100%) at 45 days post-treatment. These findings confirm that PPF effectively disrupts metamorphosis of both species, with particularly strong and prolonged effects against mosquitoes.