Four new insect growth regulators (IGRs) and a slow-release formulation of a currently-used IGR were evaluated for the control of Culex peus and Cx. quinquefasciatus in dairy wastewater lagoons. The IGR AC-291898 (CME 13406) proved highly efficacious, producing 100% control for one week and about 98% control for two weeks at the rate of 0.05 lb AI/acre (0.056 kg/ha). The IGR XRD-473 produced similar results at this rate. The effective rate of these two compounds seems to be in the range of 0.05 to 0.1 lb AI/acre (0.056-0.11 kg/ha). A granular formulation of S-31183 (0.5 G) applied at 0.05 lb AI/acre (0.056 kg/ha) yielded mediocre reduction whereas fenoxycarb EC 1 at up to 0.25 lb AI/acre (0.28 kg/ha) and methoprene 4% slow release pellets at up to 1.0 lb AI/acre (1.12 kg/ha) produced little or no control of Culex in the dairy wastewater lagoons. These compounds need to be applied at higher rates or suitable formulations will have to be developed to achieve satisfactory control.