Bacillus thuringiensis serotype israelensis (Bti) is a group of bacteria used as biological control agents for larvae stages of certain dipterans. Bti, along with other B. thuringiensis products, produces toxins lethal to various species of mosquitoes, fungus gnats, and blackflies but which have negligible effects on other organisms. The major advantage of B. thuringiensis products is that they are thought to affect few non-target species. However, even though Bti may have minimal direct effects on non-target organisms, it carries the potential for knock-on effects on food webs and other ecosystem properties, including biodiversity and ecosystem functioning.
Bti strains possess the pBtoxis plasmid which encodes numerous Cry (a δ-endotoxin) and Cyt toxins, including Cry4, Cry10, Cry11, Cyt1, and Cyt2. The crystal aggregation which these toxins form contains at least four major toxic components, but the extent to which each Cry and Cyt protein is represented is not known and likely to vary with strain and formulation. Both Cry and Cyt proteins are pore-forming toxins; they lyse midgut epithelial cells by inserting into the target cell membrane and forming pores.
