Man and Mosquitoes on Cousin island

DEET confuses Mozzies

DEET confuses Mozzies

“Cousin  island is a MUST see – mozzies or not” said Varun Sharma the host of  Inside  Luxury  Travel, a TV program aired to millions around  the world. Mosquitoes on Cousin Island Special Reserve are particularly voracious this year. Swarms even follow people to the boats as they board to leave! It’s a huge problem because we cannot spray the air or water bodies with chemicals as that would destroy a large part of the ecosystem. Insect species as well as the endangered birds eating them would be devastated.

Visitors to Cousin are warned beforehand to carry personal mosquito repellent, But many arriving on this award-winning nature reserve still find that they are bitten. Basically, their repellent just does not work. As a result Nature Seychelles has had to distribute free repellent containing a substance called DEET. This is the best deterrent against the “pesky mozzies”.

When applied to the skin’s surface, DEET drives away mozzies looking for a free lunch (or dinner). But it can also keep the insects from ever getting close enough to land. Scientists have not really understood how the chemical works.  It was always thought that DEET was effective because it was repulsive or toxic to mosquitoes.

Now, a newly published paper in the prestigious journal Nature has shown that DEET is so successful because it works by targeting a mosquito’s sense of smell.

“The effects of DEET are not straightforward,” Maurizio Pellegrino, one of the authors  of the  paper, told the on line magazine Science News. “We think the insect doesn’t know exactly what it is smelling.” Pellegrino is a neuroscientist at the University of California, Berkeley.

Mosquitoes and other insects don’t have noses. They have receptors on their antennae that can pick up the chemical signature of a smell in the air. These receptors send information about the smell to the brain by way of nerve signals.

The study showed that these receptors are affected by DEET. The nerve cells sent different signals to the brain depending on whether DEET was detected alone or together with other scents.  The repellant also affected the insects’’ ability to detect other smells. As a result DEET somehow corrupts the nerve signal sent to the brain. That means DEET doesn’t necessarily drive mosquitoes away— it just confuses them so much that they fly away, says Science News.

“It’s as if you are hungry and you love hamburgers,” Pellegrino says. “If DEET is present, it doesn’t smell like hamburger anymore, even if a hamburger is right in front of you.”   So be warned – if you are visiting a mosquito infested area make sure your repellant contains DEET.

Nirmal Shah. This post first appeared in the Author’s column in the People.

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