London School of Hygiene & Tropical Medicine

Mosquitoes are able to ignore the smell of the insect repellent DEET for up to three hours after being exposed to it, according to research published in PLOS ONE.

Although most insects are strongly repelled by the smell of DEET, previous studies led by Dr James Logan have shown that some flies and mosquitoes carry a genetic change in their odour receptors that makes them insensitive to the smell.

In this new research, Dr Logan, Dr Nina Stanczyk and colleagues from the London School of Hygiene & Tropical Medicine uncovered a response in mosquitoes based on short-term changes, not genetic ones.

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 and yellow fever viruses.

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.

Dr Logan, medical entomologist and Chief Scientific Officer for the Arthropod Control Product Test Centre, said: “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.

“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. 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."

This research is part of a large programme of work on vector insects led by Dr James Logan at the School. Partly funded by the Lawes Agricultural Trust, the research was carried out in collaboration with Rothamsted Research and the University of Nottingham.

Publication

• Nina Stanczyk, John Brookfield, Linda Field, James Logan. Aedes aegypti Mosquitoes Exhibit Decreased Repellency by DEET following Previous Exposure. PLOS ONE. doi:10.1371/journal.pone.0054438

Video

• Nina Stanczyk – changing resistance to DEET in mosquitoes

Podcast

• February 2013 podcast - includes Nina talking about her mosquito research

Learn more about DEET

• DEET - Frequently Asked Questions