Deet Insect Repellant Seems to be Losing its Effectiveness Against Mosquitos

Scientists say that the widely used inspect repellant Deet looks to be losing its effectiveness against mosquitos. According to researchers from the London School of Hygiene and Tropical Medicine, they've found that mosquitos are first deterred by the substance but then later ignore it.

Deet was first developed by the U.S. military following its experience of jungle warfare in World War II. Deet - or N,N-diethyl-meta-toluamide - is one of the most widely used active ingredients in inspect repellants. The researchers say that additional research is need to find alternatives.

The scientists carried out their research on Aedes aegypti, a species of mosquito that spreads dengue and yellow fever.

For years, it wasn't clear exactly how the chemical worked, but recent studies suggested that insects simply don't like the smell. There are now concerns that some mosquitos are growing resistant to it. In order to find out more, the scientists took the A. aegypti mosquitos in the lab, and then tempted them with a human arm covered in Deet.

As was expected, the repellant deterred the mosquitos from their potential snack. However, when the same mosquitos were offered another chance to feat on a human arm a few hours later, the researchers found that the Deet was not as effective.

In order to determine why this might be happening, the researchers attached electrodes to the insects' antenna.

Dr. James Logon from the London School of Hygiene and Tropical Medicine said:

"We were able to record the response of the receptors on the antenna to Deet, and what we found was the mosquitoes were no longer as sensitive to the chemical, so they weren't picking it up as well.

There is something about being exposed to the chemical that first time that changes their olfactory system - changes their sense of smell - and their ability to smell Deet, which makes it less effective."

Previous research by the same team found that genetic changes to the same species of mosquito can make them immune to Deet, but it wasn't clear if there were any mosquitos in the wild like this.

Dr. Logan says that it is vital to understand both these permanent genetic and temporary olfactory changes that are going on. He added:

"Mosquitoes are very good at evolving very very quickly."

Dr. Logan emphasized that the findings shouldn't stop people from using Deet in high risk areas, but said that the findings would help scientists who are trying to find new versions that could be effective. To follow up on this study, the researchers are now planning to find out how long the effect lasts after the initial exposure to Deet.

The study's findings were published in the journal Plos One.