Bacillus sphaericus is a spore-forming rod that is readily found in nature. It has been isolated from mosquito larvae, and much research has been conducted on several strains of this bacterium that are insecticidal to several species of mosquitoes. Bacillus sphaericus does not produce a parasporal body or β-exotoxin as does B. thuringiensis. However, there is a proteinaceous toxin located in the spore coat. Susceptible mosquito larvae consume the spore and partly digest the spore wall, releasing a toxin. This toxin causes feeding inhibition, swelling of the midgut cells, body tremors, and then death. Death can occur as soon as 0.5 h after consumption of the spores. Like B. thuringiensis, B. sphaericus is produced in submerged culture.
