How to Kill Mosquito Larva

You may find your yard plagued by mosquitoes, particularly if it includes a fountain, pond or other water feature. While many mosquitoes don't pose much of a threat to humans other than the incessant itching that accompanies their bites, some can transmit dangerous diseases, such as West Nile virus, encephalitis and malaria. The key to eradicating these pests is prevention -- and to do that you need to kill the larvae, the life stage a mosquito is in right after it hatches.

The best way to prevent mosquitoes from laying eggs that will hatch into larvae is to make sure your yard contains no standing water. Even a small amount of standing water, such as a shallow layer in the bottom of a watering can or rainwater accumulating in tires, plastic sheeting, wheelbarrows and other containers, can easily become a breeding ground.

This doesn't mean you have to get rid of your beloved fountain or pond, however. Implement these tips to help reduce eggs.

Keep deep water features and ponds -- preferably at least 2 feet deep. Larvae prefer shallow waters.

Increase circulation with a waterfall or pump so that you don't have standing water.

Keep your water features as free of plants and vegetation as you can tolerate -- particularly if the water is stagnant.

Consider adding mosquitofish to your pond to eat eggs and larvae.

Mosquitofish are small, but are very aggressive, so don't put them in with other fish or amphibians. Don't release these fish into natural bodies of water -- they can disturb ecosystems in which they are not naturally found.

Mosquito eggs are very tiny and hatch very quickly, typically within 24 hours, so it's difficult to get rid of them. Mosquito larvae can't fly away, however, so it's much easier to kill mosquitoes in the larval stage to prevent an adult infestation.

The most effective way to kill mosquito larvae is to apply a larvicide to water where eggs and larvae are accumulating.

Bti larvicides are made from metabolites of the bacterium Bacillus thuringiensis israelensis and are poisonous to mosquito and fly larvae, killing them within a few days. The larvicide won't harm other helpful predatory insects, such as dragonflies, however.

Bti larvicides are available in granule or pellet forms. Read the label for specific instructions. Apply the larvicide by sprinkling it into standing water according to the manufacturer's instructions. For example, one larvicide manufacturer states to apply 1 teaspoon per 25 square feet of its Bti product uniformly over standing water and to reapply every seven to 14 days. Other Bti larvicides can be effective for up to a month before you'll need to reapply.

IGR larvicides interfere with the larvae's natural molting process. They take a little longer to kill larvae than Bti larvicides, and they affect most young insects, including helpful ones like bees. IGRs also come in granule form and can typically be applied at a rate of 1/2 to 1 teaspoon per 25 square feet of water. Check the product's label for specific application rates. Sprinkle the granules evenly over the affected area and reapply once a month, or as often as directed by the manufacturer.

Wear gloves, designated clothing and a mask when applying larvicides, as they're harmful if inhaled or absorbed through the skin. Use designated measuring tools for larvicides that aren't used for food. Wash your clothes and hands immediately after applying any larvicide or pesticide. Get to fresh air immediately if you inhale a Bti product or its dust, and call 911 immediately if you're having trouble breathing. Rinse affected skin for 15 to 20 minutes, and call a poison control center or a doctor immediately if a larvicide comes in contact with your skin.

For a nonchemical solution, add a few tablespoons of mineral oil to water features in your yard or garden. The oil will form a thin layer over the surface, drowning the larvae. You'll need enough oil to cover the surface of the water. Don't put mineral oil in water with fish, however.