De-Buzzing Mosquitoes the Natural Way

In the fifth century, B.C.E., when Herodotus visited Egypt, he noticed that people slept under nets to avoid mosquitoes. More than 2,000 years later, people are still trying to elude the biting bug. With thousands of species to their name, mosquitoes thrive worldwide. They lay their eggs on water, so they are especially populous in places like Key Biscayne, Florida, near the Everglades. A few years ago Patricia Weinman, a Key Biscayne resident, experienced how pesticides can be more harmful than the bugs themselves.

Cause for Concern

In April 1997, Weinman, eight months pregnant, went to a neighbor's party. "We didn't hear the mosquito truck," she says. Sent by Dade county in a routine effort to kill mosquitoes - and not required to broadcast a warning - it was spraying malathion. "It fogged the inside of the house," Weinman recalls. "Every window was open." Within five minutes of the truck's passing, Weinman threw up. Within 48 hours, six of the eight children present developed respiratory reactions. Weinman's doctor assured her that malathion exposure has been shown to cause birth defects only in the first trimester, but she can't forget that the organophosphate, related to nerve gas, is a possible carcinogen linked to eye disorders, immune system disruptions, and genetic damage.

In Wilmette, Illinois, the North Shore Mosquito Abatement District (NSMAD) was regularly spraying resmethrin, a synthetic pyrethroid that can cause asthma and skin irritation, at night. NSMAD did not publicize its tactics or announce spray schedules, so "most people don't know about the program," says Jack Richman who, with concerned neighbors, told NSMAD that they wanted the routine spraying to stop. In December 1996, NSMAD agreed to a permanent ban.

One reason for the existence of Mosquito Abatement District (MADs) in almost every state is that the bugs can carry diseases like West Nile and other encephalitis viruses, dengue fever, yellow fever, and malaria (which kills over one million people every year). Malaria was virtually eradicated here by the 1950s, in part through widespread use of DDT, but the threat of mosquito-borne disease remains. Jay Feldman, executive director of Beyond Pesticides, says, "There is a crisis orientation to mosquito control, and it means (MADs) have gone from using organochlorines (like DDT) to organophosphates." Organophosphates act by interfering with the nervous systems of insects and sometimes other species, including humans. MADs commonly use the organophosphate pesticides malathion, naled (corrosive to the skin and eyes), and resmethrin, a synthetic pyrethroid suspected of disrupting hormone functions.

Integrated Pest Management

"Pesticide is the easy way out," says Gerard Ferrentino, director of the Urban Integrated Pest Management Program at Cornell University. Less toxic methods are more time-consuming, but they can be just as effective because they prevent mosquitoes at the source - in water - by killing larvae, as opposed to focusing on adult insects.

Responsible controllers use Integrated Pest Management (IPM): They monitor mosquito populations, target larvae, and spray only as a last resort. To reduce larvae populations, many MADs use Bacillus thuringiensis israelensis, or BTI, a bacteria that damages the mosquito's stomach or the larvae. Because it targets only mosquitoes, black flies, and some midges, BTI is considered safe for humans and natural systems. MADs also may use natural larvae predators, such as mosquito fish (Gambusia), stickleback, or guppies. (MADs should carefully consider the introduction of non-native fish species; often these fish work best in artificial water-bodies.) Some MADs practice what John Rusmisel, district manager of California's Alameda county MAD, calls "wetland enhancement" - increasing water circulation and displeasing the stagnant-water-loving mosquito. While this may alter the environment, it's better than the old practice of draining valuable wetlands. MADs may also use an insect growth regulator like methoprene, which interferes with the maturation of several insects. Methoprene is considered safe for mammals, but may harm freshwater invertebrates.

Sometimes MADs decide they have to spray for adult mosquitoes - if a West Nile or other encephalitis outbreak is a concern, for example. If your neighborhood is on the hit list, "stay inside," advises Bill Quarles, managing editor of The IPM Practitioner, a publication of the Bio-Integral Resource Center (BIRC), and don't forget to bring your pets in too. "Wait for it to settle," Quarles adds: a pesticide can be most dangerous when inhaled. Keep windows and doors closed and the air conditioner off for as long as you can stand it, preferably an hour.

Weinman, in Key Biscayne, convinced Dade County to strap a siren to the spray truck. That way, people can at least reduce their exposure. What's most important is that people are informed. "Too often," Feldman says, "people see the trucks coming to spray, and they don't know where the decisions are being made."

Molly Rauch is a health writer in New York.