Four formulations of an insect growth regulator, Bay Sir 8514 (a benzoylurea compound), were tested against 2 species of riceland mosquito larvae, Anopheles quadrimaculatus and Psorophora columbiae. Formulations of 25% WP, 0.5% G and 065 EC (65 g/liter) were tested at dosages of 14, 28, 56, and 84 g ai/ha in small plots. The 14 g ai/ha rate was ineffective for all formulations while the 28, 56 and 84 g ai/ha provided 100% mortality through 48 hr posttreatment. The 84 g ai/ha rate gave complete control through 7 days posttreatment. A 4 F formulation was applied aerially at rates of 24.9 and 49 g ai/ha to a 9.7 ha rice field. The 24.5 g ai/ha rate provided marginal control at 24 hr posttreatment but failed to control larvae at 48 hr. At 49 g ai/ha, the material provided control through the 48 hr posttreatment.