A study was undertaken to determine the effects of suspended and dissolved soil constituents on the residual larvicidal effectiveness of Bacillus thuringiensis var. israelensis in large outdoor artificial containers. Mortality decreased progressively with time although one formulation was still effective 4 days posttreatment. The presence of soil constituents was associated with a lowering of larval mortality. In the absence of soil constituents, stirring the medium tended to enhance the duration of effective control, while in the presence of soil constituents stirring tended to reduce the duration of effective control. Settling patterns of the Bti formulations were also affected by the presence of soil constituents. Bti tended to settle out faster in those troughs containing soil, probably because of adsorption to the soil particles.
