The goals of this research were 1) to provide nutritional information that would be useful for the classification of Bacillus sphaericus, a heterogenous bacterial species, 2) to determine nutritional characteristics that would assist in the design of a selective medium for the mosquito pathogenic strains of B. sphaericus and 3) to determine the effect of carbon supplementation of complex media on sporulation and mosquito toxicity of B. sphaericus. In general, the pathogenic strains which constitute DNA homology group IIA of the species, grew with a greater variety of compounds as sole carbon sources than did the non-pathogenic strains of the other homology groups. Within homology group IIA, strains of phage group 3, which are the most toxic, grew with the largest number of compounds as sole carbon sources. However, the nutritional characteristics did not allow the unequivocal differentiation of any one DNA homology group or phage group from all of the other groups. It was possible to differentiate a DNA homology group or phage group from some of the other groups. A defined medium containing malate and acetate as carbon sources was found to enable the cells to produce 1.1x10⁸ spores/ml and thus would be useful for studying the physiology of sporulation. Eighteen of 22 pathogenic strains were capable of growth in a liquid, defined medium with arginine as the sole carbon source, while only 2 of 17 non-pathogenic strains were capable of growth under these conditions. Thus, arginine may be useful as the carbon source in a selective medium for the mosquito pathogenic strains. Of several compounds which could be used by B. sphaericus as sole carbon sources, acetate was the most useful in increasing sporulation and mosquito toxicity when added as a supplement to a nutrient broth-yeast extract-mineral salts medium. A glycerol supplement to this medium led to accumulation of acetic acid and suppression of sporulation and toxin formation. An acetate supplement and a mineral salts (Ca²⁺, Mg²⁺, Mn²⁺) supplement were found to increase sporulation in a fishmeal medium and thus may be useful for commercial production of mosquito larvicides from B. sphaericus. / M.S.