by Whit Gibbons

May 24, 2009

Q: We began having mosquitoes in our backyard this year about a month earlier than usual. What can we do to reduce the number of or even eliminate these itchy nuisances?

A: Mosquitoes were out earlier in some regions because we had more winter and early spring rains than in recent years, when many areas suffered from drought conditions. Rains followed by warmer than normal temperatures on some days created ideal conditions for many species of mosquitoes to complete their life cycle and reach the blood sucking stage we all despise.

More than 3,500 species of mosquitoes exist, and like many other groups of animals and plants, the highest diversity is in the tropics. But the temperate zone where we live has its share of species. Also like other organisms with many species, mosquitoes differ considerably in their natural history, including one group that does not even bite people. The basic life cycle of a mosquito, like that of flies, grasshoppers, and many other insects, starts with the egg, which becomes a larva, which develops into a pupa before becoming an adult. Mosquito larvae and pupae are the "wigglers" (also called "wrigglers") seen flipping around in shallow standing water.

One of the basic steps in reducing the number of mosquitoes around a house is to eliminate standing water. The problem is that amounts as negligible as that collected in a dead magnolia leaf, an un-emptied rain gauge, or a low spot in a house gutter can become a mosquito nursery where eggs are laid and larvae and pupae thrive. Old tires and tree holes can also collect water and are actually preferred egg-laying sites for some mosquitoes. Some kinds of mosquitoes even lay their eggs on dry soil in depressions that later fill with water, stimulating the eggs to hatch. Sprinkler systems that keep grass and shrubs looking nice often provide all the water some mosquitoes need to start the cycle.

The aquatic stages last for a few days to a week or more, depending on the species and on the ambient temperature. Adult mosquitoes can live for days or weeks. Only the females suck blood, as part of the reproductive cycle. The blood is used to provide nourishment to the eggs while they are in the female's body. When one batch of eggs is laid, she is ready for another blood meal to get the next batch ready. Male mosquitoes, benign creatures that have no interest in humans, feed on nectar.

People attempt to eliminate mosquito problems in many ways, including neighborhood mosquito trucks, backyard mosquito traps, handheld mosquito foggers, and the numerous insect repellents on the market. The strategy of one of my daughters is to stand close to her husband when mosquitoes are around. He apparently attracts all of them, and they no longer find her as palatable. As a general rule, mosquitoes are attracted to warm body temperatures, which we all have, and carbon dioxide, which we all exhale. I know two people whose body temperature runs about a degree below normal, and invariably they are not bitten by mosquitoes while others around them are.

One satisfying tactic in the war against mosquitoes, besides swatting the life out of them when they land on your arm, is to set up a mosquito decoy site. Put a bowl or glass of water somewhere in your yard, such as on a deck or porch, and check it daily. If wrigglers are present, one of the blood-sucking mosquitoes laid her eggs a few days earlier. Give the wrigglers a day or so before you pour the water out on dry ground to kill them. Then refill the container for the next round. You can enjoy knowing you have scored a minor victory over one female mosquito and her insidious progeny. Also, the decoy lets you know that mosquitoes have recently laid their eggs so the time has come to search for other standing water around the house. Incidentally, a dab of toothpaste is a quick and effective way to stop the itching from bites by mosquitoes whose mothers don't fall for the decoy.

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