Better Ways to Swat Mosquitoes

Getting rid of the swarming summertime pests doesn’t have to involve harsh pesticides or gimmicky products, but it does require vigilance

08-01-2009 // Hannah Schardt
Mosquito on human skin

Every summer, it seems, a new gadget promises to eliminate the seasonal onslaught of backyard mosquitoes: a fan to blow the pests away, a vacuum to trap them, a zapper to, well, zap them into oblivion.

Add these contraptions to the candles, sprays and lotions that are intended to repel the insects, and home mosquito control makes up a multimillion-dollar segment of the multibillion-dollar pest control industry.

But do any of these products work? Perhaps more important: Do some of them do harm, either to human health or to the environment?

Keeping mosquito populations in check is not only a matter of comfort. "There is a public health threat," says Peter Bosak, superintendent of the Cape May County Department of Mosquito Control in New Jersey and an adjunct assistant professor of Rutgers University's Center for Vector Biology. While tropical regions are generally hardest hit by serious diseases such as malaria, North America has also seen recent seasonal outbreaks of mosquito-borne illnesses, particularly West Nile virus.

For people who want to keep their yards both livable for humans and ecologically healthy during the buggy summer months, here's the bad news: There is no effective mosquito solution as simple as buying a zapper or lighting a citronella candle. Still, that doesn't mean homeowners are helpless.

Consider the following steps to combatting mosquitoes:

Play water detective.

Experts agree that the best way to get rid of the pesky insects is the same it has always been: Prevent and eliminate standing water where mosquitoes could lay their eggs. The eggs and larvae of many mosquito species, including the distinctively striped Asian tiger that has invaded many U.S. communities over the past few decades, bide their time over the winter and spring in containers—even tiny ones—that collect rainwater. "I've seen larvae in bottle caps," says Bosak, adding that people tend to forget to check for standing water in places they can't see, such as gutters.

If you have an ornamental pond in your yard, find out if your local vector control department hands out mosquitofish, or Gambusia. As with all species not native to your region, exercise caution in releasing the fish.

If you collect rainwater for irrigation, be sure to put a screen or filter—even an old pair of pantyhose will work—over the opening of the barrel. If your yard has any unavoidable standing water, such as a drain, Bosak recommends using mosquito "dunks"—usually donut-shaped disks of biopesticide that kill mosquito larvae but are harmless to humans, pets and wildlife.

Remember that “natural” or “plant-based” doesn’t always mean safe—or effective.

The pesticides known as pyrethrins, for example, are made from the extract of chrysanthemum plants: plant-based, yes, but also highly toxic to fish, tadpoles and beneficial insects, says Bosak. Even concentrated garlic sprays, one of the most widely advertised “natural” mosquito repellents, may repel bees and other pollinators as well. Conversely, some garden centers now advertise a citronella-scented geranium as a natural way to discourage mosquitoes from lingering. The plant may indeed be safe, but it also contains no citronella oil and has no apparent effect on the mosquitoes.

Go with what works.

Studies have routinely shown disappointing results for just about every nonchemical means of repelling or killing adult mosquitoes: ultrasonic repellents, zappers and traps. Though a stiff breeze can deter mosquitoes from biting, backyard fans are limited in their effectiveness. Besides, who really wants to barbecue in gale-force winds?

What does work, aside from a strict no-standing-water regimen, is personal repellent sprayed on clothes and exposed skin. The most popular of these is the chemical N,N-diethyl-m-toluamide, or DEET, and for good reason: A 2007 study comparing the effectiveness of various mosquito repellents found that DEET-based products protected humans against mosquito bites for as long as 5 hours. Because of rare cases of human adverse reactions to the chemical, some people are reluctant to use DEET, or to use it in a high enough concentration to be effective. There are other options, including oil of lemon eucalyptus, a natural repellent that the U.S. Centers for Disease Control (CDC) says provides “reasonably long-lasting protection.” Regardless of which repellent you use, always read and follow the manufacturer’s directions. For more about safe use of repellents, visit the CDC website.

Call in the pros.

 Almost every state or municipality has some sort of vector control agency—often run out of the health department. Bosak recommends making use of the agency’s expertise. “Generally, homeowners don’t do a thorough job,” he says, of eliminating mosquito habitat from their properties. He and his colleagues often receive complaints from homeowners who say they have tried unsuccessfully to rid their yards of the pests. “And then we go out there and find mosquito habitat all over the property,” he says.

Along with a practiced eye, a vector control officer has the advantage of knowing the enemy. After identifying the species, the officer can search for habitat based on the insect’s biology. For example, some species lay eggs in tree holes, making them adaptable to water-filled children’s toys or empty pots. Other species’ larvae are found only in salt marshes or larger bodies of water.

However, the biggest reason to call in a professional, Bosak says, is that “most mosquito problems are not generated right on the property,” but rather come from nearby habitat. A vector control officer can look beyond a backyard to a larger area for the source of a mosquito infestation.

“Our first priority is some sort of water management,” he says, to cut off the mosquito supply at the larval stage—a much easier solution than combating the adults. “Once they’re on wing, they are much harder to control.”

Hannah Schardt is a senior associate editor of this magazine.

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