Distribution of mosquitocidal Bacillus thuringiensis and Bacillus sphaericus from sediment samples in Florida

A spore-forming soil bacterium, Bacillus thuringiensis subsp. israelensis has been used most widely and extensively in many regions of the world to control mosquito and blackfly larvae. It contains four major proteins in three different inclusion types assembled into a spherical parasporal body. Although no resistance to B. thuringiensis subsp. israelensis has been reported in the field yet, laboratory selection of mosquitoes with B. thuringiensis subsp. israelensis Cry proteins results in high levels of resistance. Furthermore, mosquito resistance to any of these proteins results in significant cross-resistance to the others. Another spore-forming bacterium, B. sphaericus also has been used to control mosquito larvae. However, as this bacterium contains only a single binary toxin, high levels of resistance to B. sphaericus have already been reported in the field in several countries. Consequently, there is an urgent need to search for and isolate new indigenous and more effective mosquitocidal bacterial strains. Therefore, in this study, we have screened sediment samples from various mosquito-breeding sites in Florida to isolate novel mosquitocidal bacilli with high toxicity. The results showed that mosquitocidal B. thuringiensis and B. sphaericus can be found almost everywhere.