The efficacy and persistence of sustained-release methoprene (Altosid) pellets were evaluated at rates of 3.4 and 9.0 kg/ha against Aedes mosquitoes through 7 flood cycles (126 days) in an irrigated pasture. At both rates, the pellets provided greater than 98% control through 2 flood cycles, or 20 days posttreatment, and greater than 80% control through 5 flood cycles, or 69 days posttreatment.