Mosquito dunks are used in biological control of mosquitoes. It is usually used to kill mosquitoes when they are still in larvae form. The dunks are a solid form of Bacillus thuringiensis israelensis (Bti). These are usually available in solid rings with a diameter of 2 inches and a thickness of ½ inch. These rings usually have a small hole in the center. The rings float on water and release Bti which settles to the bottom of water. The larvae eat these and die.

The mosquito dunks remain useful for a period of 30 days. That means that it will be able to kill the larvae upto 30 days from when it is released in water. Moreover, alternate wetting and drying does not diminish their properties. Therefore, dunks can be used in places where drying and wetting takes place, such as places where periodic flooding occurs.

The mosquito dunks can cover a reasonably large area. Usually one dunk is recommended for 25-100 square feet of water surface area, regardless of its depth. For efficient use in small areas, ¼ part of a dunk can be used for 1-5 square feet of water surface area. These dunks are completely harmless for other species, such as birds, fishes, plants and pets. Due to this advantage, the dunks can be used practically everywhere where water is retained, even in the tree crotch, which can become a breeding ground for the mosquitoes otherwise.

The dunks usually have a hole in the center, which is used to keep it in place with the help of a string or a stake. This helps in using dunks where water can wash away the dunks. Therefore, the dunks can also be used on running water. Usually the dunks float on water and slowly release the Bti which kills the larvae. By placing them in a preferred location, where mosquito larvae population is comparatively more than other areas, the dunks can be effectively used to kill them.

As mentioned earlier, the dunks can be practically used anywhere where water is clogged. The potential breeding grounds of mosquitoes may include flower pots, bird baths, tree holes and old tires. Other places where the dunks can be used include rain barrels, roof gutters and other such areas that have standing water. After placing the dunks, one need not inspect it regularly for its effectiveness, as it automatically performs its duty.

However, caution must be taken while using the dunks, so that it does not mix with foodstuff. If taken orally, it can be harmful for people. The dunks should also be kept away from children and should be stored in a place inaccessible to children.

The mosquito dunks are a slow and steady, but sure way, to get rid of mosquitoes. It kills the mosquitoes before they become old enough to bite. Being solid and easy to use, these can be handled by anybody without having any special knowledge of the product and its usage. These are also effective enough for a long period and hence can be used for a longer lasting effect.