Summit Mosquito Dunks® kills mosquitoes before they can become flying, biting, disease-carrying adults. The active ingredient in Mosquito Dunks® is Bacillus thuringiensis subspecies israelensis. (B.t.i.). B.t.i. is a bacterium that is deadly to mosquito larvae but harmless to other living things. Mosquito Dunks® can be placed in water troughs, koi ponds, birdbaths, rain barrels or any place where water collects and remains for periods of time. When female mosquitoes lay their eggs in standing water treated with a Mosquito Dunk®, the larvae will hatch and begin to eat the B.t.i. The B.t.i. will kill the mosquito larvae before they can grow up to become biting and disease-spreading adults.