Efficacy of Bacillus sphaericus and Bacillus thuringiensis var. israelensis for control of Culex pipiens and floodwater Aedes larvae in Iowa.

Granular and flowable concentrate formulations of Bacillus thuringiensis var. israelensis provided a 90-100% reduction in Aedes vexans and Culex spp. larvae in natural larval habitats. A briquet formulation of B. thuringiensis was less effective, providing a 12-76% reduction. No residual activity occurred in sites treated with B. thuringiensis. Granular formulations of Bacillus sphaericus (2.78-8.42 kg/ha) caused a 100% reduction in Culex pipiens larvae in natural sites and artificial pools. Bacillus sphaericus also controlled (84-98% reduction) a mixed population of Aedes trivittatus and Cx. pipiens in subplots of a retention pond. In field sites, B. sphaericus continued to control Cx. pipiens larvae for 96 hr.