The relationship between the quality of water and the presence of mosquito larvae in the growth and maintenance of Bacillus sphaericus was examined. Persistence and growth of the bacteria was monitored in three water qualities: primary and secondary sewer and spring water. Results indicate that B. sphaericus not only persists and remains toxic in all water types for up to 30 days but that it is present in higher concentrations for significantly longer periods of time where larvae are present prior to inoculation. Tests indicate B. sphaericus grows in the larval cadaver and is released into the surrounding water as the cadaver disintegrates. Outdoor experiments support the above findings and indicate the cadaver provides protection for the bacteria from the deleterious effects of sunlight.