Mosquito Bt Floating Donuts/Dunks (Pack of 6)These are a must in my wildlife pond! They keep mosquitos from breeding until beneficial insects and tadpoles take over. Mosquito Bt floating dunks come in a pack of 6. They offer a reliable and long lasting way to control mosquito populations. This helps prevent mosquitoes from becoming a problem. These dunks are specially designed to float on the surface of water bodies such as ponds, birdbaths, and rain barrels, where mosquitoes typically lay their