By Jennifer Lilonsky ( | First Posted: Feb 21, 2013 06:05 PM EST

(Photo : Reuters )

Mosquitoes are developing a resistance to the popular insect repellent DEET, according to a study conducted by researchers at the London School of Hygiene and Tropical Medicine.

The study examined the Aedes aegypti species of mosquito and its findings revealed that mosquitoes are deterred by the repellent at first, but then disregard it later.

Aedes aegypti mosquitoes are responsible for spreading dengue and yellow fever.

"The more we can understand about how repellents work and how mosquitoes detect them, the better we can work out ways to get around the problem when they do become resistant to repellents," said Dr. James Logan from the London School of Hygiene and Tropical Medicine.

DEET, or N,N-diethyl-meta-toluamide, is a commonly used active ingredient in many insect repellent formulations and was first developed by the U.S. during World War II.

While the specifics as to why DEET is an effective line of defense against mosquitoes are unclear, research has suggested that the insects do not like the smell of the chemical.

Researchers conducted the study by tempting the mosquitoes with a human arm that was covered in DEET and the repellent was observed to be working effectively.

But after a few hours, the same mosquitoes were given the opportunity to feed on the human arm and researchers observed that the DEET was less effective.

"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," Logan said.

"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."

But Logan said that these findings should not stop people from using DEET.

The research team is planning to examine other species of mosquitoes in a follow-up study.


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