A Mosquito Dunk looks like a small, beige donut which floats on standing water. As the Dunk? slowly dissolves, it releases a bacterium which is toxic to all species of mosquito larvae. Each dunk kills mosquito larvae for 30 days or more. Approved for use in organic production Each dunk covers up to 100 square feet of water, regardless of depth for 30 days or more Use Mosquito Dunks? in any standing water including rain barrels, bird baths, tree holes, elevator shafts, planter reservoirs, rain gutters, etc