DEET, which is known chemically as N,N-diethyl-meta-toluamide, is a powerful insect repellent used to deter biting insects, such as mosquitoes and ticks, which spread diseases like lyme disease and yellow fever. DEET was formulated by the United States Army in 1946 and registered for public use in 1957. Due to concerns about exposure to the chemical, an extensive safety review was completed by the Environmental Protection Agency in 1998, finding that the short-term exposure common for the use of repellents containing DEET does not pose a health risk for humans.
How DEET Deters Mosquitoes
Though the chemical has been used for decades, how it works has not been fully understood. What has been known is that the chemical does not harm or kill the insects. More recently, researchers have discovered that, in mosquitoes, the compound is sensed, or smelled if looking for an equivalent human sense, by an odor-sensing receptor on the antennae of the bug. When the receptor picks up the molecule, the mosquito is deterred from landing on the surface where the chemical has been applied.
How Mosquitoes Inherit DEET Resistance
Studies by Rothamsted Research in the UK have shown that roughly 13 percent of Aedes aegypti females in laboratory populations (i.e. disease free) are not deterred by the chemical, as shown by them landing on DEET-sprayed arms of volunteers. In one generation of breeding, the resistance increased to 50 percent.
Over subsequent generations, this proportion of resistant mosquitoes remained stable, and breeding with DEET-sensitive mosquitoes resulted in 50 percent of the offspring being resistant. These findings indicate that a single dominant gene is the reason behind the resistance. However, researchers have not yet identified which gene it is, but have narrowed it down to changes in a specific neuron type on the antennae.
How DEET-resistant Mosquitoes May Affect Humans
The common active ingredient in insect repellents, or bug spray, is DEET. Though the inherited resistance was shown in a lab, it indicates that mosquitoes harbor a gene that, if turned on, makes them resistant to current repellents. Female mosquitoes bite animals, including humans, for the nutrients in their blood. Some species of mosquitoes spread disease when they bite a person, including Aedes aegypti mosquitoes, spreading, for example, yellow fever and dengue fever. Resistant populations of mosquitoes would increase the people bitten, which could lead to increased incidence of disease.
The solution for the time being is to limit the exposure of mosquitoes to DEET in order to limit genetic selection for resistance. Alternative methods of pest control may aid in the process. In tropical regions where malaria is endemic, nets are used to prevent mosquitoes from biting people in their sleep. In addition, the U.S. Centers for Disease Control and Prevention endorsed two chemical deterrents in April 2005: picaridin (sold as Cutter Advanced) and oil of lemon eucalyptus.
Resources:
U.S. Environmental Protection Agency, "DEET fact sheet," March 23, 2007 (accessed May 27, 2010).
Janelle Weaver, Nature News, "Mosquitoes inherit DEET resistance." May 3, 2010 (accessed May 27, 2010). doi:10.1038/news.2010.216
Joan Roach, National Geographic News, "Beat bugs without DEET." July 26, 2005 (accessed May 27, 2010).
Alicia Mae Prater - Alicia received her doctorate in Experimental Pathology in 2007. She has been a freelance writer and scientific editor since 2008.
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