The newly synthesized pyridyl ether compound 4-phenoxyphenyl (RS)-2-(2-pyridyloxy) propyl ether (S-31183), which acts as a juvenile hormone, was evaluated for larvicidal potency against mosquitoes. The residual activity of three formulations, solubilized emulsifiable concentrate (SEC), wettable powder (WP) and granule (G), were compared under laboratory and field conditions. In the laboratory experiment, the granular formulation was most effective against the larvae of Culex pipiens pallens, Aedes aegypti and Anopheles stephensi. Under field conditions also, the granular formulation was more effective both against C. pipiens pallens that are susceptible and those resistant to organophosphorus compounds than a WP formulation.