Tag Archives: mosquitoes

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.

Conservation hurts!

Lately,  visitors to Cousin Island Special Reserve have remarked about the increase in mosquitoes.  Island management has noticed a swell in numbers during certain, usually short, periods in the past few years. Mosquito densities vary between seasons, and in drier seasons they are few and go virtually unnoticed. Recent heavy rainfall have contributed to the current numbers.

“After heavy rainfall they seem unavoidable,” explains Ian, Cousin’s manager. “We don’t use pesticides because this is a Nature Reserve, so we can’t control them in this manner. We however advise visitors to carry repellent, particularly that which contains a certain percentage of DEET, which is very effective. In addition we provide repellent to visitors upon arrival.”

“It is variable, some years we do not have mosquitoes at all,” echoes Riaz Aumeeruddy, Nature Seychelles’ Science Coordinator. “We have noticed a reduction as the season has began to change and we have a stronger wind blowing.”

In reality, the mosquitoes haven’t stopped visitors enjoying the 90 minutes tour of the island during this time. The wardens explain to visitors that the mosquitoes do not carry Malaria, can be controlled with repellent and when bitten, after the initial itch most people recover quickly after application of ointment. Indeed the majority of reviews and visitors’ comments recorded have one thing they agreed on completely: a visit to the island is not to be missed.

“Cousin Island is a MUST see… mozzies or not …” says Varun Sharma of the hit series Inside Luxury Travel, who began his blog post about his visit there by declaring, “I hate mosquitoes!” before proceeding to describe Cousin as filled with wonderful biodiversity.

The scientists, researchers and volunteers who arrive during this season and must contend with the mosquitoes also agree that one gets used to them. These comments are rewarding as Cousin Island and the vital conservation work done there depend largely on eco-tourism revenues.

Science officer Mary (R) and volunteer covered in mosquitoes as they tag tortoises

Science officer Mary (R) and volunteer covered in mosquitoes as they tag tortoises

Mosquitoes are common in all parts of the world. There are over 3000 species. A majority of species do not bite humans (only a few hundred do). Some are pollinators and food for animals including fish. But in the tropics where they are responsible for the spread of Malaria, Rift Valley fever, Chikungunya and West Nile viruses, sentiments way heavily towards their complete eradication, although means and consensus on the impact this would have on the natural order of things have not been found.