The requirements for growth, sporulation and the pathogenicity of Tolypocladium cylindrosporum and Culicinomyces clavisporus, two pathogens of mosquitoes, have been investigated. T. cylindrosporum produced blastospores and conidiospores in submerged liquid culture. Blastospores developed during early to mid exponential phase and conidiospores later. Sporulation and growth were influenced by sources of nitrogen, carbon and inorganic nutrients. A particularly important discovery was the value of vegetable oil, or vegetable oil components, for fungal nutrition and maintenance of friability of broken cereal grain used in solid substrate fermentation. On grains, only conidiospores were produced, the best yields being on 40 ml H₂O/50 g grain with optimal amounts of vegetable oil. Spore survival and maintenance of virulence during storage at ambient temperature were improved considerably by the addition of compatible inorganic nutrients. Blastospores were more virulent than conidiospores by 100-fold. The effectiveness of spores on aedine and anopheline larvae varied, depending on whether the spores were allowed to settle in the water, probably due to different larval feeding habits. C. clavisporus resembled T. cylindrosporum except that it sporulated over a narrower pH range and, on solid substrates, it required whole vegetable oil with lower yields on constituent fatty acids. The virulence of C. clavisporus conidia was comparable to that of T. cylindrosporum blastospores. The possibilities of using these two easily produced fungi as mycolarvicides for the control of mosquitoes are discussed. Use of semi-solid media is probably best for local production in developing countries.