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[pct-l] A replacement for DEET?

I posted this on BPL too - Dick in Stehekin, WA
Reprinted from ScienceDaily Magazine ...
Source:             American Chemical Society
Date Posted:    Tuesday, August 28, 2001
Web Address:   http://www.sciencedaily.com/releases/2001/08/010828075659.ht=

Catnip Repels Mosquitoes More Effectively Than DEET
CHICAGO, August 27 - Researchers report that nepetalactone, the essential
oil in catnip that gives the plant its characteristic odor, is about ten
times more effective at repelling mosquitoes than DEET - the compound used
in most commercial insect repellents.
The finding was reported today at the 222nd national meeting of the America=
Chemical Society, the world's largest scientific society, by the same Iowa
State University research group that two years ago discovered that catnip
also repels cockroaches.
Entomologist Chris Peterson, Ph.D., with Joel Coats, Ph.D., chair of the
university's entomology department, led the effort to test catnip's ability
to repel mosquitoes. Peterson, a former post-doctoral research associate at
the school, is now with the U.S. Department of Agriculture Forest Service,
Wood Products Insects Research Unit, in Starkville, Miss.
While they used so-called yellow fever mosquitoes (Aedes aegypti) - one of
several species of mosquitoes found in the United States - Peterson says
catnip should work against all types of mosquitoes.
Aedes aegypti, which can carry the yellow fever virus from one host to
another, is found in most parts of the United States. Yellow fever itself,
however, only occurs in Africa and South America, according to the Centers
for Disease Control. Vaccines and mosquito control programs have essentiall=
wiped out the disease in the United States, although there have been
isolated reports of unvaccinated travelers returning with the disease. The
last reported outbreak in this country was in 1905.
Peterson put groups of 20 mosquitoes in a two-foot glass tube, half of whic=
was treated with nepetalactone. After 10 minutes, only an average of 20
percent - about four mosquitoes - remained on the side of the tube treated
with a high dose (1.0 percent) of the oil. In the low-dose test (0.1
percent) with nepetalactone, an average of 25 percent - five mosquitoes -
stayed on the treated side. The same tests with DEET (diethyl-m-toluamide)
resulted in approximately 40 percent to 45 percent - eight-nine mosquitoes =
remaining on the treated side.
In the laboratory, repellency is measured on a scale ranging from +100
percent, considered highly repellent, to -100 percent, considered a strong
attractant. A compound with a +100 percent repellency rating would repel al=
mosquitoes, while -100 percent would attract them all. A rating of zero
means half of the insects would stay on the treated side and half on the
untreated side. In Peterson's tests, catnip ranged from +49 percent to +59
percent at high doses, and +39 percent to +53 percent at low doses. By
comparison, at the same doses, DEET's repellency was only about +10 percent
in this bioassay, he notes.
Peterson says nepetalactone is about 10 times more effective than DEET
because it takes about one-tenth as much nepetalactone as DEET to have the
same effect. Most commercial insect repellents contain about 5 percent to 2=
percent DEET. Presumably, much less catnip oil would be needed in a
formulation to have the same level of repellency as a DEET-based repellent.
Why catnip repels mosquitoes is still a mystery, says Peterson. "It might
simply be acting as an irritant or they don't like the smell. But nobody
really knows why insect repellents work."
No animal or human tests are yet scheduled for nepetalactone, although
Peterson is hopeful that will take place in the future.
If subsequent testing shows nepetalactone is safe for people, Peterson
thinks it would not be too difficult to commercialize it as an insect
repellent. Extracting nepetalactone oil from catnip is fairly easily, he
says. "Any high school science lab would have the equipment to distill this=
and on the industrial scale it's quite easy."
Catnip is a perennial herb belonging to the mint family and grows wild in
most parts of the United States, although it also is cultivated for
commercial use. Catnip is native to Europe and was introduced to this
country in the late 18th century. It is primarily known for the stimulating
effect it has on cats, although some people use the leaves in tea, as a mea=
tenderizer and even as a folk treatment for fevers, colds, cramps and
A patent application for the use of catnip compounds as insect repellents
was submitted last year by the Iowa State University Research Foundation.
Funding for the research was from the Iowa Agriculture Experiment Station.
Chris Peterson, Ph.D., is a former post-doctoral research associate at Iowa
State University in Ames, Iowa, and is now a Research Entomologist with the
U.S. Department of Agriculture Forest Service, Wood Products Insect Researc=
Service, in Starkville, Miss.
Joel R. Coats, Ph.D., is professor of entomology and toxicology and Chair o=
the Department of Entomology at Iowa State University in Ames, Iowa.

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