Ponds and other areas of standing water less than 24 inches deep provide a breeding ground for mosquitoes, which inflict itchy bites and transmit diseases. If draining the water isn't an option, mosquitofish, larvicides or insect growth regulators provide control. You can also reduce the numbers of mosquito larvae through cultural methods.
Many native freshwater fish eat mosquito larvae. These fish are often small and dull-colored, which helps them escape the attention of predatory birds.
Eastern mudminnow (Umbra pygmaea), eastern mosquitofish (Gambusia holbrooki) and lined topminnow (Fundulus lineolatus) are some native fish that eat mosquito larvae. Pond supply stores, garden centers and aquariums may sell mosquitofish, and in some areas of the United States it's legal to collect them from local ponds and other open areas of fresh water.
Add one mosquitofish per 2 to 5 gallons of standing water to control most mosquito larvae.
Mosquito larvicides release substances into standing water that control mosquito larvae over a set period. A larvicide that controls larvae but has little effect on beneficial insects is Bacillus thuringiensis israelensis, a bacteria that poisons the stomachs of larvae. The bacteria or their spores are contained in a disk, which floats on the water surface, gradually releasing its active ingredient.
Bti products can irritate the eyes. Put on gloves and safety goggles when handling them. Use one disk of a product containing 10.31 percent Bti on an area of standing water up to 100 feet square, or more disks if the water is heavily polluted. The disk will take up to two days to control the larvae, and the effects last up to 30 days.
Insect Growth Regulators
Interfering with the natural growth stages of insects, insect growth regulators take several days to begin working. Products containing methoprene are insect growth regulators, and they affect the juvenile stages of many insects as well as mosquitoes. Methoprene is mixed with inactive ingredients in a solid object to be placed in the water.
A product containing 8.62 percent methoprene controls mosquito larvae in standing water for 60 days. Use on product per 1,500 gallons or 100 square feet of water.
Cultural controls can reduce the numbers of mosquito larvae in standing water. Some effective controls include:
- Removing excess vegetation on or overhanging the standing water.
- Installing a fountain or waterfall to circulate the water.
- Increasing the depth of the standing water to deeper than 24 inches
- Avoiding the use of insecticides, which control mosquito larvae predators, such as dragonflies