Does spraying for adult mosquitoes reduce the incidence of West Nile Virus (WNV) in humans? Science has not answered that question. We do know that eliminating mosquito breeding sites, larviciding (killing larvae with a nontoxic product), and personal protection are more effective means of preventing WNV, and they are less harmful to human health and the environment.

Boulder County sprays for adult mosquitoes as part of its mosquito-control program. The active ingredients of the products it uses are permethrin and piperonyl butoxide (PBO). The EPA has classified both ingredients as possible carcinogens. The City of Boulder has approved the potential use of similar products.

Permethrin, a synthetic pyrethroid, is a neurotoxin capable of producing tremors, headaches, and memory loss. Research suggests it may cause immune-system damage and may act as an endocrine disruptor. Research on lab animals suggests infants are more sensitive than adults to permethrin and that it may affect neonatal brain development. In clinical studies, people with allergies, asthma, and chemical sensitivities reported severe adverse health effects from permethrin exposure at the recommended usage. Permethrin is highly toxic to fish and other aquatic organisms.

PBO is added to permethrin to increase its potency and persistence and works by shutting down enzymes that detoxify pyrethroids, making people, as well as pests, more vulnerable to pesticide exposure.

Don’t let spraying give you a false sense of security. Personal protection is the best prevention.

• Drain all sources of standing water on your property. If you have permanent standing water on your property, learn about nontoxic methods of larval control, such as mosquito-eating fish and Bacillus thuringiensis israelensis (Bti) larvicide.
• Limit outdoor activities between dusk and dawn. Wear a long-sleeved shirt, long pants, and socks.
• Know your insect repellents. DEET provides the longest-lasting protection, according to a New England Journal of Medicine (NEJM) study, but it carries its own risks. In research at Duke University, exposure to DEET or DEET plus permethrin led to neurobehavioral deficits and neuronal degeneration in lab animals, even in the absence of overt signs of neurotoxicity.

Want to try a natural repellent instead? In the NEJM study, Bite Blocker (2 percent soy oil) provided complete protection under lab conditions for an average of 1½ hours (range: 16 to 195 minutes). And Repel Lemon Eucalyptus Insect Repellent averaged 2 hours of protection (60 to 217 minutes). Beware: Other natural products tested averaged less than 20 minutes of protection. A newer study also found Bite Blocker and Repel to be significantly more effective than other natural repellents. The CDC and the EPA have now approved oil of lemon eucalyptus for use in insect repellents.