Mosquitoes exposed to DEET once are less repelled by it a few hours later

Mosquitoes are able to ignore the smell of the insect repellent DEET within a few hours of being exposed to it, according to research published February 20 in the open access journal PLOS ONE by James Logan, Nina Stanczyk and colleagues from the London School of Hygiene & Tropical Medicine, UK. Though most insects are strongly repelled by the smell of DEET, previous studies by Logan's research group have shown that some flies and mosquitoes carry a genetic change in their odor receptors that makes them insensitive to this smell. The new results reported in thePLOS ONE study uncover a response in mosquitoes based on short-term changes, not genetic ones.

"Our study shows that the effects of this exposure last up to three hours. We will be doing further research to determine how long the effect lasts," says Logan.

In this study, the authors tested changes in responses to DEET in Aedes aegypti mosquitoes, which are notorious for biting during the day and are capable of transmitting dengue fever. They found that a brief exposure to DEET was sufficient to make some mosquitoes less sensitive to the repellent. Three hours after the exposure, these mosquitoes were not deterred from seeking attractants like heat and human skin despite the presence of DEET. The researchers found that this insensitivity to the smell could be correlated to a decrease in the sensitivity of odor receptors on the mosquito's antennae following a previous exposure. "We think that the mosquitoes are habituating to the repellent, similar to a phenomenon seen with the human sense of smell also. However, the human olfactory system is very different from a mosquito's, so the mechanism involved in this case is likely to be very different," explains Logan.

He adds, "This doesn't mean that we should stop using repellents -- on the contrary, DEET is a very good repellent, and is still recommended for use in high risk areas. However, we are keeping a close eye on how mosquitoes can overcome the repellent and ways in which we can combat this."