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Mosquitoes learn to ignore DEET repellent

WebMD UK Health News
Medically Reviewed by Dr Rob Hicks

22nd February 2013 - Mosquitoes are able to ignore the smell of one of the most popular insect repellent ingredients a few hours after first being exposed to it.

London School of Hygiene and Tropical Medicine researchers have found a short term response which makes individual mosquitoes less sensitive to the smell of the DEET chemical, rather than a major genetic change.

Experts say this doesn't mean people should stop using DEET based repellents. However, they are monitoring the situation and looking for ways to overcome the resistance.

Mosquito risk

Mosquitoes aren’t a major concern in the UK, but on holiday abroad, in some places they can carry diseases like dengue fever and malaria.

DEET, or diethyltoluamide, is one of the most commonly used repellents which the NHS says is effective in sprays, roll-ons, sticks and creams.

Laboratory and field tests have shown it can repel 100% of mosquitoes. However, there's evidence that certain individual insects are not repelled by DEET.

Previous London School of Hygiene and Tropical Medicine research has found some flies and mosquitoes carry a genetic change in their odour receptors that makes them insensitive to the smell of DEET.

The new study, published in PLOS ONE, has revealed Aedes aegypti  mosquitoes learn to ignore the smell of DEET for a period of time after a brief exposure to it.

The testing is done with someone putting their arm into a cage containing mosquitoes.

Three hours after exposure, despite use of DEET protection, mosquitoes were attracted to human heat and skin again.

Keep using protection

Researchers are looking at different concentrations of repellent and carrying out tests to see how long it takes for the mosquitoes antennae to return to normal so they can be kept away by DEET again.

In a statement, Dr James Logan, medical entomologist and chief scientific officer for the Arthropod Control Product Test Centre, says: "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."

Reviewed on February 22, 2013

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