Why Insect Repellent May Be No Match for Mutant Mosquitoes

Takepart.com

Here’s some news that will surely make you want to strap on your backpack and head out to the woods: The insect repellent DEET is likely losing its ability to fend off mosquitoes.

According to laboratory research by the London School of Hygiene and Tropical Medicine, mosquitoes that were initially repelled by DEET later began to ignore the presence of the chemical entirely when feeding on human flesh.

DEET was created by the U.S. military in 1946, and has been widely used in popular insect repellents for more than 50 years. The EPA estimates that each year over one-third of Americans are exposed to DEET.

But evidence has been building that mosquitoes can develop resistance to repellents and insecticides. Scientists in London wanted to figure out just how quickly that process occurs for the Aedes aegypti, a species of mosquito that can spread yellow fever and dengue, a potentially deadly illness that infects between 50 and 100 million people around the world each year. 

The researchers presented test mosquitoes with a delicious human arm covered in DEET. At first, mosquitoes were repelled and didn’t land to feed. 

Several hours later, the mosquitoes were exposed to the arm again. This time, despite the DEET, many of them began to “probe” the arm for blood. 

“They may have adapted to DEET, possibly by associating it with the presence of a host arm, and were able to ‘overcome’ the natural repellent effect,” the authors wrote in their paper, which was published this week in the journal PLOS ONE.

To figure out why this was occurring, the researchers attached receptors to the antennae of the mosquitoes, and found that the mosquitoes were no longer as sensitive to DEET after a span of just three hours. 

“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,” Dr. James Logan, of the London School of Hygiene and Tropical Medicine, told the BBC.

The researchers recommended that alternatives to DEET be developed. In the future, they plan to study how quickly DEET wears off on other species of mosquitoes, like the ones that transmit malaria, another serious and sometimes fatal disease that affects 216 people around the world each year.   

In the past, the use of DEET has been a critical component of government recommendations for reducing the risk of contracting mosquito-borne illnesses. The EPA has written that despite its potency, DEET does not prevent a health concern to the U.S. public when sprayed in recommended doses. The agency has admitted that DEET is slightly toxic to fish and birds, and can be found in drinking water in some parts of the country.  

Other researchers are exploring different strategies for mosquito control—like genetically engineering mosquitoes to be resistant to disease. This comes at a time when the potential impacts of viral-carrying mosquitos are set to multiply. The World Health Organization has said that climate change will likely make some mosquito populations even more dangerous, when warming temperatures make viruses like malaria and dengue more aggressive.

“Our current strategies, like insecticides and repellents, are losing their effectiveness,” says Michael Riehle, associate professor of entomology at the University of Arizona, in his interview with TakePart. “The idea is to release genetically-engineered mosquitoes that are resistant to deadly viruses like malaria into the wild to replace the wild mosquito population.”

Riehle says scientists are making progress on creating a mechanism of replacing infectious mosquitoes with non-infectious counterparts. “To replace them, you have to give non-infectious mosquitoes some sort of genetic advantage,” he said. And therein lies the challenge.

As Loz Blain of Gizmag has pointed out, genetically engineering mosquitoes raises a number of “ethical and environmental quandaries.” It could cause some species of mosquitoes to go extinct, for instance, or bring about irreparable damage to certain food webs. Some argue that these effects pale in comparison to the urgent need to save lives and eradicate diseases like malaria.

Critics have warned that genetically-engineered mosquitoes should undergo rigorous testing along with public consultation about the dangers of introducing engineered mosquitoes into the wild before any GE mosquitoes take flight.   

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• Op-Ed: Expanding on the Moral Logic of Climate Communication


Alison Fairbrother is the director of the nonpartisan Public Trust Project, which investigates and reports on misrepresentations of science by corporations and government. She has written for the Washington Monthly, the Washington Spectator, Grist, and Politics Daily, among others. Alison is based in Washington DC. @adfairbrother | TakePart.com

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