Bti is a bacterium that occurs naturally in soil. Bti is short for Bacillus thuringiensis subspecies israelensis. It has been used in mosquito control for more than 30 years. According to the EPA ...

This method uses a “Mosquito Dunk”, a larvicide that uses Bti, (Bti is short for Bacillus thuringiensis subspecies israelensis) a bacterium that produces a toxin that only kills larvae.