Mosquito-toxic Bacillus sphaericus strains may synthesise a variety of toxins. This is the principal active ingredient of the spores of the highly toxic Bacillus sphaericus strains in current use for biological control of mosquitoes. The 100kDa Mtx1 toxin which is highly active but is unstable when produced in Bacillus sphaericus owing to the action of a proteinase. The Mtx2 and Mtx3 toxins which are related to each other and to the pore forming epsilon-toxin of Clostridium perfringens.
Different strains produce different insecticidal crystal toxins on sporulation.
See the Bt toxin nomenclature database for details. The 3-dimensional structures of some crystal toxins have been determined. Follow this link for Dr Berry's Tutorial on Toxin Structure . These toxins show a range of insecticidal activities, each one specific for a small group of insect species. Bt israelensis produces at least six toxins that are specific for mosquitoes.