American Chemical Society: Catnip Repels Mosquitoes More Effectively Than DEET

http://www.sciencedaily.com/releases/2001/08/010828075659.htm

Source: American Chemical Society
http://www.acs.org/

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
American 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 essentially 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
which 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 all 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 25 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 meat tenderizer and even as a folk treatment for fevers,
colds, cramps and migraines.

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 Research Service, in Starkville, Miss.

Joel R. Coats, Ph.D., is professor of entomology and toxicology and
Chair of the Department of Entomology at Iowa State University in
Ames, Iowa.

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Received on Thu Mar 20 14:15:27 2003