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.
