Mosquitoes Can Ignore DEET: Insect Repellent Ineffective

They buzz, they suck your blood and now it may be impossible to deter them. The insect repellent, DEET, seems to be losing its effectiveness against mosquitoes.

The research, published in the journal PLOS One, was conducted by James Logan, Nina Stanczyk and colleagues from the London School of Hygiene & Tropical Medicine. Although insects are strongly repelled by the smell of DEET, previous research by Logan's group had shown that some flies and mosquitoes carry a genetic change in their odor receptors that cause them to not be bothered by the scent of the insect repellent. Because of this, Logan and his team decided to test the effectiveness of the repellent on mosquitoes.

The researchers tested changes in responses to DEET in Aedes aegypti mosquitoes, which are notorious for biting people during the day and can transmit dengue fever, a virus that starts with a sudden high fever and includes a rash. They exposed the mosquitoes to the DEET and found that, after only three hours, the mosquitoes were not deterred from seeking attractants such as heat and human skin, despite the presence of the insect repellent.

In order to investigate exactly what was happening, the scientists attached electrodes to the insects' antennae. They were then able to record the response of the receptors on the antennae to DEET; apparently, the mosquitoes were no longer as sensitive to the chemical, and so weren't picking it up as well.

Researchers suspected that, like the human sense of smell, the odor receptors on the mosquito's antennae following previous exposure became desensitized to the smell after long periods.

These findings could have widespread implications for those living or travelling to tropical areas. DEET is used heavily in order to deter mosquitoes that carry sicknesses that include West Nile and other viruses. Yet since the repellent quickly loses its effectiveness, it shows that people may need to use other means in order to combat mosquitoes.

"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," said Logan in an interview with e! Science News. "However, we are keeping a close eye on how mosquitoes can overcome the repellent and ways in which we can combat this."