The grey flesh fly Parasarcophaga argyrostoma plays a role in human cutaneous wounds and eye myiasis and it is also known as parasitoid of various animals. The present study aimed to investigate the efficacy of Methoprene on survival, development and metamorphosis of this fly species. Five dose levels (10.0, 5.0, 1.0, 0.1 and 0.01µg/larva) of Methoprene was topically applied onto the early last instar larvae and prepupae. Methoprene exhibited larvicidal, pupicidal and adulticidal activities against P. argyrostoma. LD₅₀ values were found 0.155 and 0.258 µg/insect after topical treatment of early last instar larvae and prepupae, respectively. The maximal body weight of treated larvae was considerably decreased. The duration of treated larvae was prolonged. The coefficient of growth of treated larvae was depressed. The pupal duration was remarkably prolonged. Some larval-pupal intermediates had been produced, only at the higher two doses. Topical treatment of prepupae only with the lower two doses induced a state of 'permanent prepupae'. The treated last instar larvae pupated in regressed rate. The pupation rate was slightly regressed after topical treatment of prepupae only with the lower two doses. The adult emergence of flies was completely blocked after topical treatment of either the early last instar larvae or prepupae with the highest dose of Methoprene. At other dose levels, the adult eclosion of flies was partially blocked. Different percentages of deformed pupaeand adults were recorded.