Released: May 23, 2003

Some Mosquito Products Can Be Worse Than Having No Protection

MANHATTAN, Kan. – The news is simple, but not very encouraging for people who already have bought some of the "nicer" seeming mosquito repellents and controls.

The fact is, nothing repels mosquitoes better than products containing DEET (for skin and/or clothing) or permethrin (for clothing only). The more of the ingredient a product has, the longer its effects will last, said Kansas State University entomologist Ludek Zurek.

"That’s particularly important this year because West Nile virus-carrying mosquitoes are likely to be in every one of the lower 48 states this summer. The peak mosquito season in Kansas is June through September," warned Zurek, who is K-State Research and Extension’s specialist in medical- and veterinary-entomology.

Another important factor to remember, however, is that applying sunscreen and a DEET-based repellent at the same time reduces the sunscreen’s effectiveness by as much as 33 percent, he said. Plus, parents always must use caution in applying a repellent to children.

"Children are neither more nor less likely than adults to get West Nile virus. The people most at risk are the elderly and those with a compromised immune system," he said. "But children are more sensitive to repellents. So, parents must follow label directions exactly. Or, they should use a repellent for kids that’s based on soy oil and will require more frequent applications."

Zurek recommends that adults not use products that contain more than 33 percent DEET.

"Stronger isn’t better. It relates to how long a product remains effective. The easy-to-find products with about 20 percent DEET give adults four to five hours of protection. That should be plenty," he said.

In contrast, while testing some of the "nicer" repellents now on the market, researchers found that three major wristband products provide less than 1 minute of protection against mosquito bites, Zurek said. One widely-sold lotion – which word-of-mouth has "sold" as a bug repellent – actually provides about 3 minutes of protection. Its bug guard formulation protects for just 10 minutes. Its "plus" formula provides 23 bite-free minutes.

Some scientific evidence indicates that citronella candles, U-V insect killers and the so-called mosquito plant (Pelargonium citrosum) all provide LESS protection than doing nothing to control mosquitoes outdoors. Mosquito coils and ultrasonic repellers protect little better than doing nothing at all.

"In addition, I have yet to see any reliable evidence that eating bananas, vitamins or garlic; setting up a bat house on your property; or trying some similar ‘old wive’s tale’ will offer protection from mosquito bites," Zurek said.

He added that besides wearing an effective repellent, the best most people can do to limit their exposure to mosquitoes comes down to:

1. Make sure screens on doors and windows are tight and have no unmended holes.

2. Remember dawn and dusk are when mosquitoes are most active and seeking hosts.

3. When outdoors, place netting over infant carriers.

4. Empty and clean birdbaths and outdoor water bowls at least once a week.

5. Drain and/or fill tree holes, stumps, puddles and the like.

6. Eliminate or regularly empty "artificial" water containers – clogged rain gutters, empty cans and bottles, old tires (including swings), buckets, toys, boat and swimming pool covers, wheelbarrows. ...

7. Aerate ponds and pools. Or, stock them with mosquito larvae-eating fish, such as minnows or goldfish; then limit, remove or flood any edge vegetation that could block the fish from the larvae.

Rural dwellers may have special challenges, the entomologist said. Mosquitoes can breed in ditches, low spots in fields, watering tanks, stock ponds, waste lagoons and stored tires – all of which can be more or less permanent fixtures.

"An array of active ingredients are approved for the control of mosquito larvae in such situations. But you have to be careful not to apply them until they’re really needed – when you see mosquito larvae in the water – and to investigate which one product best fits your situation," Zurek said. "For example, some aren’t too effective in water clogged with algae. A number can be toxic to other insects, fish or birds."

K-State entomologists already have asked for help in tracking when the need for protection against mosquitoes becomes acute this year in a particular city or county. Kansans can provide this help by reporting newly dead bluejays, crows, ravens or raptors (birds of prey), because those birds usually are each season’s first West Nile virus victims. K-State’s Department of Entomology labs have a toll-free "dead-bird" hotline at 866-452-7810 and a Manhattan telephone number at 785-532-2569.

If a report meets certain criteria, the entomologists will ask that without actually touching the dead bird, Kansans double-bag it in plastic, seal or twist-tie both bags, freeze the resulting "package" (which will not harm food), and take it to their local K-State Research and Extension office for shipping.

That office also can provide more information about West Nile Virus, mosquito controls and repellents, Zurek said.

His free publication "Mosquitoes and West Nile Virus" was gone almost as fast as it came off the press this spring, but is available on the Web (http://www.oznet.ksu.edu/library/ENTML2/MF2571.pdf). It includes charts from the New England Journal of Medicine and the Journal of the American Mosquito Control Association. The charts rate commercial mosquito products by name on effectiveness in research trials. Zurek’s publication also discusses the factors involved in West Nile virus transmission, plus outlines possible approaches to larger-scale larvae control efforts.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Kathleen Ward, Communications Specialist
kward@oznet.ksu.edu
K-State Research& Extension News