Mosquitos are now able to ignore the scent of the insect repellent DEET three hours after being exposed to it.

The finding, published in PLoS One, suggests that even though historically, insects have been strongly repelled by the scent of DEET, other studies by Dr.James Logan reveal that some mosquitoes and flies carry a genetic alteration in their aroma receptors rendering them insensitive to the smell.

DEET is one of the most successful protectors against mosquito bites that can transmit deadly diseases, such as:

Products that have DEET come in many different forms including liquids, sprays, lotions, wristbands. DEET has been in use by the public since 1957.

In this latest study, Dr. Logan and his peers from the London School of Hygiene & Tropical Medicine discovered a response in mosquitoes that occurred due to short-term changes (not genetic ones).

The investigators examined changes in responses to DEET in Aedes aegypti mosquitoes – which are well known for biting during the day and transmit deadly diseases, such as yellow fever and dengue fever.

They discovered that a slight exposure to DEET was enough to make some mosquitoes less sensitive to the repellent.

Three hours following exposure, the mosquitoes were put off seeking out attractants like human skin and heat even though they had been previously exposed to DEET.

The investigators also saw that this ineffectiveness of the odor could be linked to a fall in the sensitivity of smell receptors on the mosquito’s antennae after an earlier 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.”

In 2008, a new class of bug repellent was found to be effective for three times longer than DEET, which is the quality standard of all repellents.

Written by Kelly Fitzgerald