Last year, several members of the Iowa State University Department of Entomology presented the results of a study on common catnip. Among their conclusions was the fact that an essential oil in catnip is 10 times more effective at repelling mosquitoes than potent chemicals such as DEET.

Date:   7/22/2006 5:35:13 PM ( 18 y ago)

Grow your own mosquito repellent

By ANN LOVEJOY
SPECIAL TO THE POST-INTELLIGENCER

The news is full of horror stories, including the spread of the West Nile Virus by mosquitoes. At the same time, a news item landed on my desk that seems to promise a simple, natural way to fend off the little buggers.

Last year, several members of the Iowa State University Department of Entomology presented the results of a study on common catnip. Among their conclusions was the fact that an essential oil in catnip is 10 times more effective at repelling mosquitoes than potent chemicals such as DEET.

DEET is currently the most common active ingredient in commercial mosquito and bug repellents. Unfortunately, many studies indicate that DEET is also a dangerous chemical for humans, especially children. A study carried out at Duke University Medical Center revealed that DEET can cause brain-cell death and may trigger behavioral changes indicative of neurological damage in rats after frequent or prolonged use.

In an effort to find a safer alternative, the scientists investigated several plant essential oils that were commonly recommended as insect repellents by organic gardeners. Catnip ranks high on the list of natural bug-busters and evidently with good reason. In the Iowa study, the researchers noted that small doses of catnip oil were at least as effective at repelling mosquitoes as 10 times larger doses of DEET (which was used at typical recommended application rates for commercial products).

While the researchers don't know why mosquitoes don't like catnip oil, they do know a good thing when they see it. Recently, the Iowa State University Research Foundation applied for a patent for the use of catnip essential oils as compounds. Within a few years, we'll probably see many safe, non-toxic mosquito repellents on the market.

In the meantime, why not grow some mosquito repellent of your own? If you have a sunny, well-drained patch of lean garden soil, try planting some catnip. The plant you need is a perennial herb called Nepeta cataria. Closely related to ornamental catmint, or Nepeta faassenii (or N. mussinii), catnip is generally grown as a cat-pleasing or medicinal tea herb rather than for its looks.

Catnip is far from ugly, but its gentle blue flowers are definitely out-produced by its masses of softly hairy, gray-green foliage. Like most herbs, it prefers well-drained soil and plenty of sunlight. If you garden on heavy clay, you may succeed better with catnip and other herbs if you give them a mounded bed or grow them on a slope to improve winter drainage.

The first year you plant catnip, you may need to water it a time or two, especially if next summer is as hot and dry as this one has been. However, fall-planted herbs, including catnip, often need very little water the following summer. Fall and winter rains can help plants create deep, strong root systems that increase the natural drought resistance of catnip and many other herbs.

Don't feed your fall-planted herbs, but do mix some compost into their planting soil. A mix of half compost, half native soil is usually just right. Top off the soil with a light blanket of compost (2-3 inches) to help feed those actively growing roots through the cool months.

Even in spring, don't feed your herbs with anything but compost, or at most a mild all-purpose organic fertilizer such as Whitney Farms 5-5-5. Adding too much fertilizer can cause lush overgrowth in many herbs, leading to dilute or low-quality essential oil production. In some cases, herbs such as creeping thymes can be killed by commercial fertilizers, so when in doubt, use only a very mild fertilizer and apply it at half the suggested application rate.

This summer, I experimented with making both catnip vinegar spritzers and catnip infused oils. Both did a fine job of keeping mosquitoes and no-see-ums at bay during our warm summer evenings. If you would like to try this yourself, here are the simple recipes I used:


CATNIP MOSQUITO SPRITZ
MAKES ABOUT 3 CUPS

* 2 cups catnip, stemmed
* 3-4 cups mild rice vinegar

Rinse herbs, roll lightly with a rolling pin, then place them in a clean quart jar and cover with vinegar. Seal jar and store in a dark cupboard for two weeks.

Shake jar lightly every day or so for two weeks. Strain into a clean jar, seal and refrigerate for up to 6 months unused.

To use, spritz on exposed skin and around outdoor dining area.


CATNIP AND ROSEMARY MOSQUITO CHASING OIL
MAKES ABOUT 2 CUPS.

* 2 cups catnip, stemmed
* 1 cup rosemary, cut in 6-inch sprigs
* 2 cups grapeseed oil or any light body-care oil

Roll herbs lightly with a rolling pin and pack into a clean jar. Cover with oil, seal jar and place in a cool, dark cupboard for two weeks.

Shake jar lightly every day or so for two weeks. Strain into a clean jar, seal and refrigerate for up to 8 months unused.

To use, rub on exposed skin.


http://seattlepi.nwsource.com/nwgardens/90412_lovejoy10.shtml

/27/01

Contacts:
Joel Coats, Entomology, (515) 294-7400
Chris Peterson, U.S. Forest Service, (662) 320-3859
Brian Meyer, Agriculture Communications, (515) 294-0706

Editor's note: Joel Coats and Chris Peterson may be reached Aug. 27-29 at the American Chemical Society's annual meeting in Chicago. Numbers for the meeting's press room are (312) 329-7114 and (312) 949-3237. Coats will be back at ISU on Aug. 30.

CATNIP DRIVES CATS WILD, BUT DRIVES MOSQUITOES AWAY

AMES, Iowa -- Although it drives cats wild, catnip appears to be a big turn-off for mosquitoes.

In research conducted at Iowa State University, catnip was 10 times more effective at repelling mosquitoes than the compound used in most commercial bug repellents. The finding was reported today at the 222nd national meeting of the American Chemical Society in Chicago.

Chris Peterson and Joel Coats studied the effect of nepetalactone on mosquitoes. Nepetalactone is an essential oil in catnip that gives the plant its odor. In past studies, the researchers had found that catnip oils could repel cockroaches. Peterson recently left a post-doctoral research position at Iowa State and is now working as an entomologist with the U.S. Forest Service in Starkville, Miss. Coats is the chair of ISU's Department of Entomology.

The researchers placed groups of 20 mosquitoes in a glass tube treated on one side with a high dose of nepetalactone. After 10 minutes, an average of 80 percent of the mosquitoes had moved to the untreated side of the tube. In a low-dose test, an average of 75 percent moved to the untreated side.

The researchers conducted similar tests with DEET (diethyl-meta-toluamide), the compound used in many commercial repellents. In those tests, 55 to 60 percent of the insects moved away from the treated side.

In the laboratory, repellency is measured on a scale from 100 percent (all mosquitoes repelled) to -100 percent (all mosquitoes attracted). In the ISU tests, catnip ratings ranged from 49 to 59 percent at high doses, and 39 to 53 percent at low doses.

Peterson said it took about a tenth as much nepetalactone to have the same repellency as DEET. "In other words, nepetalactone is about 10 times more effective than DEET," he said. "Most commercial insect repellents contain about 5 to 25 percent DEET. Presumably, much less catnip oil would be needed to achieve the same repellency as a DEET-based repellent."

Why catnip repels mosquitoes remains a mystery. "It might simply be an irritant," said Peterson, "or they just don't like the smell."

No animal or human tests are scheduled for nepetalactone, although Peterson is hopeful that will take place in the future. Iowa State has submitted a patent application for the use of catnip compounds as insect repellents. The project was funded by the Iowa Agriculture and Home Economics Experiment Station.

Catnip is a perennial herb in the mint family and grows wild in most parts of the United States. It also is cultivated for commercial use. It's primarily known for its stimulating effect on cats, although some people use the leaves in tea, as a meat tenderizer and as a folk treatment for fevers, colds, cramps and migraines. The plant also is used to make light yellow dye.

 

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