Mosquitoes ‘ignore insect repellent’

Mosquitoes ignore repellent Deet after first exposure

Deet works the 1st time, but for some hours afterwards it loses its power

The frequent insect repellent Deet seems to be losing its effectiveness against mosquitoes, scientists say.

Researchers from the London School of Hygiene and Tropical Medicine say mosquitoes are first deterred by the substance, but then later ignore it.

They say more research is required to search out alternatives to Deet, which was first developed by the united states military.

The research was accomplished on Aedes aegypti, a species of mosquito that spreads dengue and yellow fever.

The findings are published within the journal Plos One.

Dr James Logan from the London School of Hygiene and Tropical Medicine, said: “The more we will understand about how repellents work and the way mosquitoes detect them, the easier we will be able to workout the way to get across the problem once they do become proof against repellents.”

Human bait

Deet – or N,N-diethyl-meta-toluamide – is among the most generally used active ingredients in insect repellents. It was developed by america military, following its experience of jungle warfare during World War II.

For a few years, it was not clear exactly how the chemical worked, but recent research means that insects simply don’t like the smell.

However, there are concerns that some mosquitoes are growing proof against it.

To discover more, researchers from the London School of Hygiene and Tropical Medicine took some A. aegypti mosquitoes within the laboratory, and tempted them with a human arm covered in Deet.

As expected, the repellent put the insects off their potential meal.

However, a couple of hours later when an identical mosquitoes were offered an opportunity to dine again, the researchers found that the Deet was less effective.

To investigate why this may be happening, the researchers attached electrodes to the insects’ antenna.

Dr Logan explained: “We were ready to record the response of the receptors at the antenna to Deet, and what we found was the mosquitoes were now not as sensitive to the chemical, so that they weren’t picking it up besides.

“There’s something about being exposed to the chemical that first time that changes their olfactory system – changes their sense of smell – and their ability to sniff Deet, which makes it less effective.”

Arms race

Earlier research by the similar team found that genetic changes to an identical species of mosquito could make them proof against Deet, even though it was not clear if there have been any mosquitoes like this inside the wild.

Dr Logan said it was vital to comprehend both these permanent genetic and temporary olfactory changes that were happening.

He said: “Mosquitoes are important at evolving very in no time.”

He stressed that the findings won’t stop people from using Deet in high risk areas, but that they might help scientists who’re looking for new versions which may be effective.

To follow up at the study, the researchers now plan to determine how long the effect lasts after the initial exposure to the chemical.

The team would also desire to study the effect in other mosquitoes, including the species that transmit malaria.