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Mosquito Genetics Is Key To Insecticide Resistance
(Beyond Pesticides, May 14, 2003)
A new study shows that mosquitoes carrying West Nile virus and malaria are resistant to organophosphate and carbamate insecticides, according to the May 9, 2003 Nature Science Update. The study, "Insecticide Resistance in Mosquito Vectors," (Nature 423(6936): 136 - 137) shows that the resistance is a result of a single genetic mutation. Mylène Weill of Montpellier University II in France, who led the study, found the mutation in the mosquito genus Anopheles gambiae (which has been found to carry malaria) and Culex pipiens (which has been found to carry West Nile virus and other insect borne diseases).

Organophosphates and carbamates bind irreversibly to the active site of an essential enzyme for normal nerve impulse transmission, acetylcholine esterase (AchE), inactivating the enzyme. The study is the first ever to have "identified the gene that encodes [AchE]" according to Dr. Weill.

The Nature Science Update article states that Weill believes that, "Despite the potential for developing new insecticides, chemical warfare is unlikely to beat the insects."

Weill is looking to continue to study other mosquitoes, including Aedes aegypti (which are known to carry dengue and yellow fevers), and whether they also have the mutation gene that results in resistance to certain insecticides.

As the weather warms, many communities will be dealing with the issue of mosquito control and West Nile virus. While recognizing the importance of West Nile virus as a public health threat, experts say it is important to realize the limited threat that mosquitoes pose. The U.S. Fish and Wildlife Service (FWS) addressed the public's heightened fear of mosquitoes based on information from the Centers for Disease Control and Prevention (CDC).

FWS states, "Contrary to media descriptions of 'the deadly West Nile virus,' [it] is rarely fatal in humans. Less than one percent of people who acquire the disease will experience severe illness." Dr. Brian Rogers, health authority in Ft. Worth, TX, says the chances of becoming seriously ill or dying from West Nile virus are "extremely minimal."

Agencies addressing West Nile virus and other insect-borne diseases, such as dengue fever, malaria, yellow fever and encephalitis, must decide the best way to protect the public. In this decision-making process, it is important to realize the limited efficacy of pesticides in controlling mosquitoes. A large part of this has to do with the inability, especially in an urban environment, to hit target insects with typical ground spraying from trucks or by aerial application.

Brian Boerner, director of Environmental Management in Ft. Worth, says, "The spraying of chemicals also has the potential of contaminating our waterways, killing the beneficial fish and organisms that feed on mosquito larva, adding harmful volatile organic chemicals to the atmosphere … and providing a potential inhalation or ingestion hazard to residents who are in affected areas shortly after spraying occurs."

Beyond Pesticides recommends an integrated approach that includes community education, prevention, monitoring, habitat modification, biological controls and bacterial larvicides (see Beyond Pesticides' Public Health Mosquito Management Strategy. For more information, see Beyond Pesticides' West Nile virus/Mosquito Management page.