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Mosquito, Tick Repellents in the Wind?
By Judy McBride
January 3, 2002
Slap, slap . . . scratch, scratch.
Its a familiar aggravation for billions of people who live with
mosquitos. But effective repellents to keep those pests from biting--and
possibly transmitting serious diseases--have been few and far between.
Now, the Agricultural Research
Service is seeking a patent on a method for selecting the most effective
version of a repellent discovered by ARS researchers more than 20 years ago.
Using the method, ARS entomologist
Jerome Klun recently
identified one version that is three to four times more effective at preventing
yellow-fever-transmitting mosquitos from biting than the original repellent.
Its also the optimal version against the species that transmits West Nile
The original repellent, called 220 for short, is based on piperidine, a
hexagonally- shaped molecule found in trace amounts in black pepper. Two other
chemical groups are attached to this hexagon, but each can attach at two
different angles. So the repellent can appear in four different versions, known
as optical isomers, that can be identified by the way they bend light rays.
The number of potential repellents is not limited to these four optical
isomers. Other chemical groups can attach to the piperidine scaffold at various
locations and angles, yielding dozens of candidates for testing, according to
Klun, at ARS Chemicals
Affecting Insect Behavior Laboratory in Beltsville, Md.
Interested companies could license the new method to select the most
effective piperidine-based isomers against ticks and other disease-transmitting
arthropods, as well as mosquitos. Unlike DEET--the principal mosquito repellent
for half a century-- piperidine-based repellents dont dissolve plastics,
such as sunglass lenses or auto paint. And early reports from an interested
company suggest they easily formulate into creams.
The original piperidine-based repellent has undergone toxicological testing
in a U.S. Army laboratory and passed muster for experimental use on people.
Also, a related repellent is being sold overseas by the pharmaceutical company
Bayer. However, products intended for commercial sale in the United States
would have to undergo additional toxicological testing required by the
Environmental Protection Agency.
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.