Kills mosquitoes before they are old enough to bite! Mosquito Dunks® is a biological insecticide (BTI) that kills the larvae of mosquitoes that transmit West Nile Virus, Zika Virus, and Dengue Fever. The only sustained release product with BTI, a bacteria toxic only to mosquito larvae, that lasts 30 days or more. Place Dunk in standing water where mosquitoes breed. Each Dunk treats 100 square feet of surface water regardless of depth. For less water, Dunks can be broken into halves or quarters. Labeled for organic gardening by the USEPA. Highly effective low impact product. Non-toxic to all other wildlife, pets, fish, and humans.