Nav: Home

What makes mosquitoes avoid DEET? An answer in their legs

April 25, 2019

Many of us slather ourselves in DEET each summer in hopes of avoiding mosquito bites, and it generally works rather well. Now, researchers reporting in the journal Current Biology on April 25th have made the surprising discovery that part of the reason for DEET's success can be found in the mosquito's legs, not their biting mouthparts.

"We show that while mosquitoes find DEET and bitters equally distasteful to ingest, only DEET repels mosquitoes on contact," said Emily Dennis (@emilyjanedennis) of The Rockefeller University and the Howard Hughes Medical Institute.

The findings may help in the quest for even better and longer lasting insect repellents, the researchers say.

Dennis along with Leslie Vosshall (@pollyp1) and colleagues had previously developed mutant mosquitoes that lose some of their sense of smell, including the part required for avoiding DEET-treated arms. While normal mosquitoes steer clear of DEET, those mutants remained attracted to people even when they were covered in the repellent. But despite that attraction, they didn't actually bite. That's because they were repelled on contact by DEET-laden skin.

The question was: Why? Other researchers showed several years ago that DEET may taste bitter and speculated that bitter taste could account for its ability to repel mosquitoes on contact.

To test this idea, the researchers first made sure that mosquitoes didn't like bitter tastes or the taste of DEET by offering them sugar water with and without DEET or another bitter compound. As expected, the insects had a clear preference for sugar water without the bitter or DEET.

Next, they put bitter compounds on their arms, and they were surprised to see that mosquitoes continued to blood feed. In fact, they'd keep on biting even when those bitter compounds were present at ten times the concentration used in the sugar-water drinking experiments.

It suggested the insects' avoidance of DEET even when they couldn't smell it wasn't due to a bad taste in their mouths. To explore further, they offered mosquitoes warm blood under a membrane that they had to puncture to drink. When DEET or the bitters were mixed into the blood, the insects weren't interested in drinking. When bitters were smeared onto the membrane, the mozzies still continued to land and drink the blood. But, they found, a layer of DEET on the membrane surface was incredibly effective in keeping the buzzing insects from making contact.

"We were confident then that DEET was doing something interesting and fairly unique on the surface of the skin," Dennis said.

Mosquitoes and other insects have tiny hairs all over their mouthparts and their legs that can sense molecules. It means that, much like our tongues, their legs have an ability to taste. Additional experiments showed the mosquitoes continued to feed on DEET-treated arms only when the researchers rigged it so that their legs did not touch the skin. It told them that a mosquito's legs are important for sensing DEET.

The study is the first to experimentally separate out the various effects of DEET and identify the parts of the body that mosquitoes need to sense the repellent. The researchers say the findings will now allow them and others to pinpoint the critical neurons and proteins involved, with important implications for the development of new repellents.

"DEET is the most effective repellent available on the market, and it's possible that other repellents fall short because they are only able to mimic one or two aspects of how DEET works," Dennis said. "If the key to DEET's effectiveness is its ability to act on all sorts of sensory systems in many ways, knowing what those are can help us screen for new potentially longer lasting repellents."
-end-
Research reported in this publication was supported by the National Institute on Deafness and Other Communication Disorders of the National Institutes of Health and was supported in part by the National Center for Advancing Translational Sciences, National Institutes of Health Clinical and Translational Science Award program. The authors declare no competing interests.

Current Biology, Dennis et al.: "Aedes aegypti Mosquitoes Use Their Legs to Sense DEET on Contact" https://www.cell.com/current-biology/fulltext/S0960-9822(19)30402-6

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.

Cell Press

Related Mosquitoes Articles:

Mated female mosquitoes are more likely to transmit malaria parasites
Female mosquitoes that have mated are more likely to transmit malaria parasites than virgin females, according to a study published Nov.
In Baltimore, lower income neighborhoods have bigger mosquitoes
Low-income urban neighborhoods not only have more mosquitoes, but they are larger-bodied, indicating that they could be more efficient at transmitting diseases.
Mosquitoes more likely to lay eggs in closely spaced habitats
Patches of standing water that are close together are more likely to be used by mosquitoes to lay eggs in than patches that are farther apart.
Why do mosquitoes choose us? Lindy McBride is on the case
Most of the 3,000+ mosquito species are opportunistic, but Princeton's Lindy McBride is most interested in the mosquitoes that scientists call 'disease vectors' -- carriers of diseases that plague humans -- some of which have evolved to bite humans almost exclusively.
Biting backfire: Some mosquitoes actually benefit from pesticide application
The common perception that pesticides reduce or eliminate target insect species may not always hold.
What makes mosquitoes avoid DEET? An answer in their legs
Many of us slather ourselves in DEET each summer in hopes of avoiding mosquito bites, and it generally works rather well.
How mosquitoes smell human sweat (and new ways to stop them)
Female mosquitoes are known to rely on an array of sensory information to find people to bite, picking up on carbon dioxide, body odor, heat, moisture, and visual cues.
Forecasting mosquitoes' global spread
New prediction models factoring in climate, urbanization and human travel and migration offer insight into the recent spread of two key disease-spreading mosquitoes -- Aedes aegypti and Aedes albopictus.
Medicating mosquitoes to fight malaria
Mosquitoes that landed on surfaces coated with the anti-malarial compound atovaquone were completely blocked from developing Plasmodium falciparum, the parasite that causes malaria, according to new research led by Harvard T.H.
Mosquitoes can hear from longer distances than previously thought
While most hearing experts would say an eardrum is required for long distance hearing, a new study from Binghamton University and Cornell University has found that Aedes aegypti mosquitos can use their antennae to detect sounds that are at least 10 meters away.
More Mosquitoes News and Mosquitoes Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.