Bti’s mode of action begins during its spore forming stage which involves the production of a protein crystal, or a parasporal body. This parasporal body consists of six δ-endotoxins (Ben-Dov, 2014). When target species such as mosquito larvae consume Bti, the δ-endotoxins bind to epithelial cells within their stomach lining where the internal stomach alkalinity activates the parasporal body toxins. The toxins are then released, causing the stomach to burst and eventually result in the death of the target larvae (Hughes et. al., 2004).
Bti can be applied into waterbodies such as lakes, ponds, and other smaller areas of collected water. Once in contact with target species such as mosquito larvae, Bti will produce activated toxins and restrict larvae development from entering the pupa and adult mosquito life stage. Fortunately, target species resistance to Bti toxins have not been observed since its discovery and Bti has remained an extremely effective control mechanism for the proliferation of mosquito larvae (Ben-Dov, 2014).
Bti, largely due to its target specific larvicidal effects, poses no toxicity risk for humans and is safe to apply in aquatic environments. Bti has also been shown to have no toxicity or adverse negative effects on fish, insects, mammals, and aquatic microorganisms (US EPA, 2022). Overall, Bti has been proven to be a safe and easy to apply biological larvicide.
Barjac, H.D. & Sutherland, D. J. (Eds.) (1990). Bacterial control of mosquitoes & black flies: Biochemistry, genetics, & applications of bacillus thuringiensis israelensis and bacillus sphaericus. Rutgers.
Ben-Dov, E. (2014). Bacillus thuringiensis subsp. israelensis and its Dipteran-specific toxins. Toxins, 6, 1222-1243.
Hughes, P.A., Stevens, M.M., Park, H., Federici, B.A., Dennis, E.S., & Akhurst, R. (2005). Response of larval Chironomus tepperi (Diptera: Chironomidae) to individual Bacillus thuringiensis var. israelensis toxins and toxin mixtures. Journal of Invertebrate Pathology, 88, 34-39.