Communities search for a safer way to kill mosquitoes
West Nile virus brings a long-simmering controversy to a boil
CORTEZ, Colorado — Susan Cowan clearly remembers eating dinner at a restaurant near her hometown of Dolores, Colo., when a mosquito bit her on the foot. Two weeks later, she was in bed with an apparent case of the flu. Eventually she tested positive for West Nile virus.
Now, a year later, she still suffers exhaustion, achiness and mental fog; some days, she cannot even drive. Today, she’s a passionate believer in the widespread spraying of pesticides. "I’ll take everybody else’s spray," she says. "I believe in spraying. I don’t care what anybody says."
Rebecca Thomas holds a different view: For years, she has fought the local Florida Mosquito Control District over pesticide spraying around the three-acre tract near Durango where she grows organic vegetables. As a child, she says, she was exposed to toxic chemicals through her father, who worked at a chemical company and came home reeking of fungicides, herbicides and pesticides.
That exposure has led to recurring bouts of muscle aches, tingling, numbness, even temporary paralysis; blood tests have found elevated levels of organophosphates, a type of pesticide used for mosquito control. Thomas believes widespread spraying is dangerous, especially for children. "Unfortunately, in our culture, we emphasize protecting ourselves from things that kill us immediately," she says, "but not things that kill us (in the) long-term."
The issue of mosquito control has long polarized residents of the West. Recently, concerns about West Nile virus, a mosquito-borne illness that is particularly dangerous for the elderly or ill, have intensified the debate. Since its arrival to the United States in 1999, West Nile — which can lead to encephalitis and meningitis — has killed close to 600 people nationwide and sickened thousands (HCN, 12/22/03: West Nile isn't just for people).
Piecemeal protectionMosquito control today is handled piecemeal by thousands of counties, municipalities and special publicly funded districts. Until the past decade, many areas concentrated on aerial fogging with pesticides such as malathion, an organophosphate that breaks down more quickly than DDT, a chemical that was banned in 1973 after its use was linked to dwindling bird populations and environmental damage (HCN, 8/2/99: DDT doesn't just fade away).
But not everyone welcomes the trucks trundling down rural streets at dusk, exuding clouds of foul-smelling spray. Toxic to fish, amphibians and honeybees, malathion has also raised ecological concerns. Organic farmers worry about drift onto their properties, and many others wonder about its impact on human health.
Some districts have switched to pyrethroids — synthetic versions of a chemical produced naturally by chrysanthemums — which smell better and are slightly less toxic than malathion. But mosquito-control experts say spraying only kills adult mosquitoes; more pupae hatch and emerge the next day.
Now, the threat of West Nile has renewed calls for aggressive spraying — even the limited use of DDT. Advocates say DDT is more effective than other pesticides precisely because it lingers in the environment. They also say it could be used safely today in small quantities for mosquito control, not as it was used in the past, when large amounts were sprayed as a general pesticide on crops such as cotton.
But Aimee Code, water-quality coordinator for the Oregon-based Northwest Coalition for Alternatives to Pesticides, points out that not all mosquito species carry West Nile. Even among people who are bitten by an infected mosquito, only 20 percent experience noticeable symptoms. Even fewer become seriously ill, she says.
The coalition frowns on all pesticide use, she says, but larvicides, which are commonly spread by hand, are preferable to aerial sprays. Code advocates common-sense measures to avoid being bitten: cutting up old tires and emptying watering cans to reduce backyard breeding sites; staying indoors from dusk to dawn; and wearing protective clothing.
An effective, or "integrated," mosquito-control program requires trapping and surveying the biting insects, locating and eliminating breeding sites, and killing larvae in natural wetlands, says Joe Conlon, technical advisor for the American Mosquito Control Association, a nonprofit trade association. One commonly used larvicide is Bti, an inert bacterium that kills mosquito larvae by binding to the receptor cells in their stomachs so they can’t feed; it is virtually nontoxic to animals, birds, fish and other insects.
In 1998, the Montezuma (County) Mosquito Control District in Colorado, one of the states hardest-hit by West Nile, switched to an integrated approach. The program, administered by Colorado Mosquito Control, Inc., employs spraying only when a trap nets a large number of mosquitoes in a particular area. This approach has slashed the amount of pesticide used from some 50 drums of malathion a year to about three of Biomist, a pyrethroid, according to Jason Carruth, district manager. Although it’s impossible to measure exactly how many mosquitoes are out there, the program has been effective: Montezuma County hasn’t had a single case of human West Nile this year.