Mosquito Attractants/Repellents - NYTimes Overview

[WestNileVirus-L Moderator's Note:
For more information about mosquito attractants and repellents, see
the Environmental Risk Analysis Program's "West Nile Virus Resources
for the General Public," Sections II "Insect Repellents" and Section
III "Mosquito Biology and Control."
Find research articles using ERAP's "West Nile Virus Bibliography of
Scientific Literature," using the search term "Mosquito
Repellents/Attractants." These resources are one click away from
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This topic has periodically been addressed on this listserv. Access
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Lois Levitan]

The New York Times
July 1, 2003
SEARCHING FOR WAYS TO COPE WITH BUZZ OF MOSQUITO SEASON

By JAMES GORMAN

It's the season of the whine - the high-pitched note that signals a
prowling mosquito near your ear, and the even more annoying
complaints emitted by humans wondering whether mosquitoes really
should have a place in the web of life.

It's also the season of gadgets and sprays. The pressure to defeat
the ubiquitous little bloodsuckers is greater than ever, since
mosquitoes may carry West Nile virus or Eastern equine encephalitis,
as well as cause the familiar red, itchy bumps. Also, mosquitoes
breed in standing water, and at least in the Northeast, a wet spring
is producing a bumper crop.

A vast arsenal is available for the mosquitophobe. A partial list
includes Mosquito Deleto, the Electronic Swatter, Mosquito PowerTrap,
Mosquito Terminator, Mosquito Magnet, the Bug Zapper, Mosquito
Control Plus, the Solar Mosquito Guard, the Dragonfly Mosquito
System, Mosquito 'Cognito, the Sonic Web and Insectivoro. Limited
space makes it impractical to list every flowering of the American
bug-killing imagination.

Apart from gadgets, there are citronella candles, sprays and lotions
galore, synthetic and natural, and clothing impregnated with
permethrin. For anyone with a taste for the primitive a full body
coat of bear fat or axle grease will discourage both insects and
unwanted suitors. So many choices: what's a poor bipedal blood meal
to do?

Joseph Conlon has some thoughts on the matter. He is an ex-Navy
entomologist who has solved numerous mosquito-related problems, like
weaning the Marine Corps from Skin So Soft in the days before it
added a new chemical repellent.

He is now the technical adviser to the American Mosquito Control
Association and is more than willing to offer advice on mosquito
defense. He favors simple, direct action, and is blunt about some of
the devices sold widely. "Don't be taken in by a lot of newfangled
gadgets," he said.

Instead, he says, you should first "know your enemy." For example, he
says he gets calls from homeowners who say, "I've got these big
mosquitoes that are bothering my kids." They're actually crane flies,
he said, which look like giant mosquitoes but don't sting or bite.

Second, eliminate breeding sources. In other words, depending on the
neighborhood you live in, either get rid of the old tires on your
front lawn or make sure water isn't accumulating in your terra cotta
garden ornaments. For ornamental pools, fish help, or there are
chemicals that kill the larvae in water.

Fix your screens, make sure the bugs aren't getting in the house
through air conditioners and consider the ultimate sacrifice: stay
inside at dusk and early morning when the mosquitoes are most active.
If you must go out to greet the dawn use insect repellents and wear
loose-fitting clothing.

Mr. Conlon was not favorably disposed toward devices that use light
to attract and electricity to fry insects. "These things are
worthless," he said. "Actually they're worse than useless." They kill
mostly larger, beneficial insects.

An often quoted study by Dr. Douglas W. Tallamy of the University of
Delaware found that less than a quarter of a percent of insects
killed by such a zapper were mosquitoes and at least 13 percent were
beneficial insects. Zappers have undergone some changes, however, and
some now use chemicals known to be effective at attracting mosquitoes.

Bats and purple martins are not much better than zappers, Mr. Conlon
said. They do eat some mosquitoes, but prefer bigger juicier meals.
Anti-mosquito plants are effective at keeping mosquitoes away from
themselves, but they won't help you much, he said. And those sonic
devices to repel mosquitoes? Tests had shown "no repellency
whatsoever," Mr. Conlon said.

Dr. Tallamy concurred. He had not researched them himself, but said,
"there's no physiological basis for them to work, and I've seen no
evidence from any study that they work." Some frequencies of sound
may, however, attract mosquitoes.

There are devices that clearly do lure and kill mosquitoes, although
that doesn't mean they'll keep you from getting bitten. Among these
are traps that use carbon dioxide and other chemicals to attract
mosquitoes, which are then killed by various means, like being
trapped until they die of dehydration. Carbon dioxide makes a
mosquito think of the warm exhalations of a person relaxing with a
book in a hammock, and they follow it. Other chemicals are known to
attract them.

"The technology behind these and the theory behind these is really
solid," Mr. Conlon said. But, how helpful they are in preventing
bites depends on the situation. On isolated barrier islands they
proved effective in reducing mosquito population. "In a subdivision
they're not going to work as well," he said, because the neighborhood
will provide a constant new supply.

Dr. Daniel L. Kline, a research entomologist at the Department of
Agriculture Center for Medical, Agricultural and Veterinary
Entomology in Gainesville, Fla., said the CO2 traps showed promise,
but agreed that their effectiveness in the typical suburban yard was
unknown. The question is how many mosquitoes you have. If you live
near a salt marsh, using one trap would be like trying to empty the
ocean with a cup.

Citronella coils and candles are weakly repellent, Mr. Conlon said,
but a cloud of smoke from a smudge pot or a cigar will work, if
you're willing to let it surround you.

Beyond clearing standing water, navigating the commercial minefield
of mosquito gadgets, and staying inside, looms the prospect of
protecting your person. Let's say you must venture into the yard, or
perhaps you are planning to walk through a swamp in August, or you're
a soldier and are being sent to an unpleasant location.

Again, Mr. Conlon does not mince words: "DEET is still king." DEET
(N, N-diethyl-m-toluamide) is the active ingredient in most
commercial insect repellents. A variety of other substances, natural
and synthetic, have some repellent effect, but DEET, said Mr. Conlon,
is so far the best. That doesn't mean, however, that you need high
concentrations. A 25 to 35 percent concentration is best, he said,
the higher concentrations don't provide much added benefit, but
simply extend the time of effectiveness.

A report last year in The New England Journal of Medicine concluded
that DEET was by far the most effective. The authors were Dr. Mark S.
Fradin, a Chapel Hill, N.C., physician, and Dr. John F. Day, a
medical entomologist at the Florida Medical Entomology Laboratory.

They reported that a 28 percent solution of DEET offered complete
protection for about five hours. A "soybean-oil-based repellent"
worked for about an hour and a half, a formula with a relatively new
chemical repellent IR3535 for about 20 minutes, and all other
botanical repellents for less than 20 minutes. "Repellent-impregnated
wristbands offered no protection."

Avon, which has added the repellent IR3535 to its popular lotion,
Skin So Soft, rejected the findings of the journal article, saying
that laboratory studies are not as effective as field studies.

Although many consumers worry about health effects of insect
repellents, the Environmental Protection Agency has declared normal
use of DEET products to pose no significant risks for children or
adults.

The American Academy of Pediatricians, a private group, takes
positions on a variety of health issues that affect children,
including the use of DEET. Its most recent advisory suggests that
DEET is appropriate for use on children when there is a concern about
insect-borne diseases, although children are much less likely than
adults to become ill from West Nile virus.

The academy recommends 30 percent as a maximum concentration and
suggests using the lowest concentration that will last for the time
spent outdoors. Products with 10 percent are effective for about two
hours.

The academy's advisory urges parents not to apply DEET more than once
a day, also good advice for adults, and not to use a product that
combines DEET with a sunscreen.

Some new products may be on the horizon. A new class of repellent,
called SS-220, has been patented by scientists working for the
Department of Agriculture and is now undergoing toxicity tests.

Dr. Kline's lab is investigating why mosquitoes find some people more
attractive than others. There is definitely "scientific merit," he
said, to the observations that one family member tends to draw
mosquitoes.

Dr. Kline said a colleague at his lab, Dr. Ulrich Bernier, had
patented several chemicals given off by unappetizing humans that seem
to serve as masking chemicals or inhibitors. Any application of this
research would be some way down the line.

A method of personal protection widely used in the military and now
sold to consumers is clothing treated with permethrin, an effective
insecticide that shouldn't be applied to the skin. With the clothing,
you still need to apply a repellent to exposed skin. The Army has
other good advice, which everyone should follow. Do not wear dog and
cat flea collars, not even on your legs, no matter how bad the bugs
are. A June bulletin on pest management from the Army warns against
wearing flea and tick collars. "Animal flea and tick collars are NOT
for human use!" the warning states.

The reason is simple. Dogs and cats don't sweat, but people do. And
sweat can release some of the pesticides from the collars so they can
be absorbed by the skin.

The precautions the military takes can also be grim. Mr. Conlon
recalled that one problem he solved in his military career involved
marine recruits at Parris Island, S.C., who were being eaten alive
when they assembled at 5:30 a.m.

That, of course, was prime mosquito time. The solution was simple.
Move the time up an hour, and have the recruits fall in at 4:30 a.m.
After all, why should marines let some insects get a jump on them?

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