Efficacy of Bacillus sphaericus 2362 formulations against floodwater mosquitoes

Four new formulations of Bacillus sphaericus 2362 yielded excellent control of floodwater mosquitoes Psorophora columbiae and Aedes nigromaculis in irrigated fields in Kings and Riverside counties of California. A primary powder formulation (ABG-6184) was the most active, producing excellent control of Ps. columbiae and Ae. nigromaculis at the rates of 0.05 to 0.5 lb/acre (0.055-0.56 kg/ha). A liquid formulation (BSP-2) was slightly less active, but was effective against the same species in the range of 1.0-1.5 lb/acre (1.12-1.68 kg/ha). Activity of the two corn cob granular formulations was largely dependent on potency (spores/gram). The high spore count granules (1.5 x 10(9) spores/gram) yielded 91 and 98% reduction of Ae. nigromaculis at the rates of 2.5 and 5.0 lb/acre (2.8 and 5.6 kg/ha), respectively. Against the same population, the lower spore count formulation (7.6 x 10(8) spores/gram) produced complete control at the rate of 10 lb/acre (11.2 kg/ha), but poor results were obtained at the rate of 5 lb/acre (5.6 kg/ha).