Female mosquitoes lay their eggs in bodies of water that stay still or move slowly. As such, mosquito larvae may develop in your water features. Within seven to 10 days of hatching, these mosquitoes become adults and may wander around the area looking for a blood meal. You can use various mosquito control methods to kill mosquito larvae.
Natural larvicides kill mosquito larvae using organic bacteria. Bacillus thuringiensis israelensis (Bti) produces crystal proteins that mosquito larvae may ingest. These proteins then damage the larvae's digestive tract and kill them. Another type of bacteria, Bacillus spahericus (Bs), also produces proteins that poison mosquito larvae. These bacterial larvicides come in granular and solid formulations. They only kill mosquitoes and flies and cause no harm to other organisms, including humans, pets, fish and plants.
Some larvicides have been specifically developed by humans to control mosquito larvae. Methoprene, an insect growth regulator, allows mosquito larvae to only develop into pupae and then kills them before they have a chance to become adults. Methoprene comes in granular and solid formulations. It may affect other insects, but it doesn't harm humans, animals or plants. Another type of chemical larvicide, temephos, contains organic phosphate compounds. Methoprene is more commonly used and you may be able to find it more easily.
If your water feature can support mosquito predators, they can both control mosquito larvae and add interest. Some fish that eat mosquito larvae include minnows, goldfish and Gambusia affinis. If you stock enough fish to reproduce, they will continuously keep your water feature free of mosquito larvae. A type of turtle known as the red-eared slider also eats mosquito larvae. Other predators include the tadpoles of some frog species, including the spadefoot toad, green treefrog, giant treefrog and European green toad.
Mosquito larvae stays near the water surface so they can breathe. You can use this behaviour to your advantage. Placing a coat of oil over the water surface prevents the mosquito larvae from breathing and suffocates them to death. Some mosquito control product manufacturers market special oils for mosquito larvae, but the University of Illinois Extension suggests that mineral oil may also be effective. The oil may harm any fish you have in the body of water.