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Mosquito and Other Insect Repellants
Insect Repellants—Plants and Products You Can Use This Summer; and New Alternatives on the Way

Q. Dear Mike: Can you suggest a good insect repellant for use on the body that will be effective against ticks, mosquitoes, etc.? Many thanks.
    ---Larry in Lewes, Delaware


A. Great question, Larry—and just in time to inform people planning to slather themselves with DEET about the dangers and limitations of that chemical repellant and their more natural alternatives.

One of my biggest concerns with DEET is that a lot of the chemical is absorbed through your skin, travels through your bloodstream and is then excreted. I don't know about you, but I already give my liver and kidneys enough work. And although DEET is effective at preventing mosquitoes from feeding, its ability to deter ticks is highly debatable.

Ticks are a subject unto themselves, so visit this previous Question of the Week for details on your tick-specific control options. And visit this previous Question of the Week for info about preventing mosquitoes from breeding on your property and some products you can use to keep outdoor areas free of the bloodsuckers.

This week, we'll focus mostly on personal mosquito protection, with a close look at two non-chemical products that have been shown to be effective: "Bite Blocker" (aka "Sting Free") and "Repel Lemon Eucalyptus Insect Repellant"; a number of plants you can utilize for protection; and some very interesting options to come. (NOTE: Many of these plants and repellants will also protect you from other pestiferous insects, like midges, no-see-ums, biting flies, and chiggers. Try several different things to see what works best against what's biting you.)

Bite Blocker: In a 2002 study published in the New England Journal of Medicine, North Carolina dermatologist Mark Fradin, M.D. found that this product provided protection from mosquito bites for an hour and half—longer than one of the DEET products he tested. Canadian researchers got much better results—three and a half hours of "complete protection" in two 1996 field trials. Bite Blocker's declared active ingredient is soybean oil, but the repellency is more likely due to the extract of lemon-scented geranium it also contains. You'll find Bite Blocker for sale in stores, and Gardens Alive sells it under the brand name "Sting Free". (Hey! Mosquitoes don't STING—they BITE!)

Repel Lemon Eucalyptus Insect Repellant: In April of last year, the Federal Centers for Disease Control finally got off their high toxin horse and acknowledged that this product "is effective at preventing mosquito bites." Previously, only chemical repellants had been so honored. In a follow up to his original study, Dr. Fradin reported that this product provided complete protection for an average of two hours under the same test conditions as Bite Blocker. As you might expect from the name, its repellency comes from a lemon-scented eucalyptus plant. Its available on the web and at camping stores—but make sure you get the right stuff. Repel also makes a lot of repellants that contain the nasty chemical DEET.

(A report in the November 6, 2004 Journal of Medical Entomology found that the Repel Lemon Eucalyptus product also provided pretty good protection against ticks.)

Anyway, many lemon-scented plants themselves provide excellent protection when you crush up their leaves and rub them on your skin. Studies at the University of Guelph in Canada found lemon thyme to be the best 'crush and rub' lemon plant repellant (62% the repellency of the nasty DEET product, "Deep Woods Off"!). But the plant itself is fairly small (although its also VERY attractive), so I use lemon balm instead; it also works great, and it's MUCH easier to grow HUGE amounts. (Warning: lemon balm grows aggressively and must be controlled.)

You can try other lemon-scented herbs as well—review the research on natural mosquito repellants and you'll find lemon-scented plants at the top of many lists. (Just don't use real lemons or other citrus—the oils are too strong and can give you a nasty rash, especially after sun exposure.) And lemon scented thyme may be effective for more than just its lemon fresh scent—regular old garden thyme (Thymus vulgaris) also scored very high in a 2005 Korean study. (I may give that easy-to-grow herb a crush and rub test this summer!)

Just remember that—with plant leaves or a commercial product—mosquitoes will bite any area left unprotected; so leave no flesh un-slathered or leafed!

On the horizon—and perhaps in your garden—catnip! Dr. Joel Coats, the Professor of Entomology and Toxicology at Iowa State University who discovered its powerful natural mosquito repellant powers, tells us that a patent has been secured and he hopes to see licensed products on the market before too much longer. (There ARE products that include catnip as an ingredient, but these are not licensed and have not been studied.)

Dr. Coates adds that his research leads him to strongly believe that a naturally occurring compound found in the peel of the Osage orange—yes, that weird pockmarked tree fruit—is even better, lasting up to six hours and repelling both ticks and mosquitoes. We'll be following this research closely.

And finally, you may have already heard news reports about a new mosquito repellant isolated from tomatoes. As the developer of this new repellant, Dr. Michael Roe, Professor of Entomology at North Carolina State explained to me recently, the active ingredient—a naturally-occurring compound known as "undecanone"—is found not in the fruit, but in the plant's stems. And not in the stems of tomatoes like the ones growing in our gardens either. Undecanone is produced in the stems of 'wild tomatoes', very hairy primitive Peruvian ancestors of our summertime favorites, whose fruits are fuzzy, like peaches. So don't waste your time rubbing your tamata plants all over yourself. Unless you simply like doing that kind of thing, of course.

Dr. Roe found that natural compounds used by this primitive plant to repel insect attack also repel mosquitoes and ticks. Tests in North Carolina and Canada have shown that the compound—now dubbed "BioUD"—provides protection as good or better than chemical repellants containing up to 30 % DEET.

The compound—already in use as a food flavoring agent—has received several US patents as an insect repellant and is worming its way through the legal process with final EPA registration approval expected this Fall. When that approval comes, " BioUD" will replace the current active ingredients in the Bite Blocker line of products.

You Bet Your Garden Question of the Week © 2006 Mike McGrath

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