Soil Bacteria that Kill Mosquito Larvae.

Background To control the deadliest mosquitoes, Bacillus thuringiensis var israelensis and Bacillus sphaericus are the tools to prevent the development of adult mosquitoes by killing the larvae in different water sources. Various countries formulated Bacillus thuringiensis and Bacillus sphaericus larvicide in different forms isolated from various sources to control mosquitoes. These bacteria are nontoxic for humans and other living organisms. In Nepal, unawareness and unavailability of these isolates made us inaccessible to these tools to control mosquito vectors. To address the increasing trend of mosquito-borne diseases in Nepal these bacteria should be included as a vector control tool. Objective To isolate and test the novel bacteria Bacillus thuringiensis and Bacillus sphaericus from the soil sample of Nepal as a biological mosquito control tool. Method Soil samples collected from seven provinces of Nepal were processed by two different techniques to isolate these two bacteria. The isolates were characterized by different staining techniques, and by larvicidal bioassay against Aedes aegypti larvae. Result From 282 soil samples analyzed by the acetate selection method 846 Bacillus thuringiensis isolates were obtained producing different types of crystal protein. Among 846 isolates only one isolate showed 100% mortality against Aedes aegypti larvae. On analysis of 32 soil samples by heat shock selection method, 11 Bacillus sphaericus and 11 Bacillus thuringiensis were obtained. Only one Bacillus sphaericus showed 25% mortality against Aedes aegypti larvae. Conclusion Two different Bacillus strains obtained from the soil sample of Nepal showed 100% and mild toxicity against Aedes aegypti larvae.