Bacillus thuringiensis israelensis (Bti) The active ingredient in
two of the most popular and environmentally-sensitive
products is a Bacillus bacterium. The bacterial cells of Bacillus thuringiensis israelensis (Bti) produce a spore and a crystalline protein toxin (endotoxin) as they develop. When the mosquito larvae ingest the spores, the endotoxin is activated by alkaline conditions and enzyme activity in the larval gut. The activated endotoxin attaches to specific receptor sites resulting in larvae paralysis and destruction of the gut wall. Larvae usually die quickly from the activity of
the toxin or stop feeding and die within 2 or 3 days from the effects of septicaemia (blood poisoning). Because the majority of aquatic invertebrates do not have alkaline guts, Bti has no effect on the majority of potential non-target organisms, although it might affect some other dipteran larvae