Mosquitoes Eating You Alive? Cheesy Feet Could be the Problem.

Here in New England, spring has most definitely sprung. And what comes after spring? Summer. That wonderful time of year when we in the Ocean State hit the beach, have cookouts, and unfortunately get bitten by mosquitoes (when we’re not in the lab, which is obviously most of the time, honest). But recent research from a group of Dutch entomologists has provided new insight into how these evil beasts track us down.

Mosquitoes, a name that comes from the Spanish or Portuguese for little fly, generally inhabit warm, wet areas of the tropics. This is primarily because female mosquitoes like to lay their eggs in swamps, and warm temperatures impact their offspring’s development. Both males and females feed on nectar, however females must take in a protein- and nutrient-rich blood meal in order to produce eggs. This behavior makes mosquitoes an efficient vector for the spread of various infectious diseases in humans and animals, including malaria, yellow fever, and dengue fever.

In 1942, a study conducted in Uganda showed that the Aedes simpsoni mosquito would preferentially bite the face of naked children (thus the effect of obstructive clothing was ruled out). This suggested that there was some kind of chemical signal being emitted in the facial region, most likely in exhaled breath. The observation lead to the finding that female mosquitoes can sense exhaled carbon dioxide from tens of meters away, and therefore home in on their blood meal target.

But in the 1990’s, researchers at Wageningen University in the Netherlands reported that different species of mosquitoes preferred different sites on the human body. Bart Knols led the study, in which he sat in a climate control room in nothing but his undies and let the bugs bite him. The researchers found that while they recapitulated the results seen in Uganda with some species of mosquitoes, Anopheles gambiae (the malaria-carrying species) primarily bit Knols on the ankles and feet. Furthermore, if Knols washed his feet with bactericidal soap the mosquitoes bit him indiscriminately. This demonstrated that the odor-producing bacteria on his feet were responsible for attracting the insects.

Limburger: A mosquito attractant (and people repellant).

Knols and his team soon realized the link between cheesy feet and, well, cheese. There are a number of different bacteria that live on our feet that produce smelly chemicals. Brevibacteria are perhaps the most pertinent bacteria to this story, as they are also found in a number of cheeses, including Limburger and Munster. These bacteria produce the sulphurous compound methanethiol, the chemical that gives both feet and these cheeses their characteristic smell. It turns out that mosquitoes can be deceived by samples of Limburger, and will land on the stuff; deluded into thinking it is a foot.

New research from this group, which comprised the doctoral work of graduate student Remco Suer, has started to get at the molecular mechanisms that underlie this cheesy affinity. Suer found that olfactory receptors on the hairs around the mosquitoes’ mouthparts could recognize a number of odorants produced by foot bacteria. But more interestingly, he found that when these receptors were excited they could no longer detect carbon dioxide. This suggests a mechanism whereby mosquitoes use carbon dioxide as a long-range signal, but once they are close to their target they switch to sensing signals from their preferred biting site. In the case of Anopheles gambiae, these short-range signals come from smelly feet.

The fact that short-range signals block the carbon dioxide signal presents a potential new strategy for mosquito control, and therefore malaria prevention. Using odorants known to block the carbon dioxide receptors, such as the cheesy smells identified in this work, mosquitoes could be diverted away from people and livestock.

I wonder if the mosquitoes here would fall for a Limburger-trap. Only one way to find out…

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Katie Pratt is a graduate student in Molecular Biology at Brown University. She has a passion for science communication, and in an attempt to bring hardcore biology and medicine to everyone, she blogs jargon-free at www.katiephd.com. Follow her escapades in the lab and online on Twitter.

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Be the first one to mind the gap by leaving the bacteria and the compound they produce as a comment and get your name in the blog along with a sweet new BenchFly mug!

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UPDATE: Congratulations to Ian Jessup – winner of this edition of Mind the Gap!

About the winner: Ian is a freshly minted undergraduate with a double major in biology and chemistry, emphasis in cellular & molecular biology, from the Metropolitan State College of Denver. He has a perverse fascination with organisms that can kill you in less time than it takes to drink a cup of coffee, and enjoys long walks through rattlesnake infested territory.

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About the prize: In addition to fame and glory beyond their wildest dreams, winners receive our new hot-off-the-presses large (15 oz) BenchFly mug to help quench their unending thirst for scientific knowledge… or coffee.


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Miss a previous edition of Mind the Gap? We’ve got you covered:

Dirty Mouth? Clean it Up with Cancer Screening

Because in Space…It’s Always 5 O’Clock Somewhere

Curry: Now Good for Detecting Explosions, Not Just Causing Them

So You Thought Eating Poop Was Bad For You?

Are Fatty Acids the Cure for PMS?

Botanical Sleuthing Recovered Endangered Daisy

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7 comments so far. Join The Discussion

  1. Ian Jessup

    wrote on May 11, 2011 at 2:10 pm

    Brevibacterium linens, and methanethiol

  2. Leon Van Eck

    wrote on May 11, 2011 at 2:13 pm

    I'm going to guess they are Brevibacteria and that the chemical they produce is methyl mercaptan (also known as methanethiol), a breakdown product of the amino acid methionine.

  3. India

    wrote on May 11, 2011 at 2:13 pm

    Brevibacteria produce methanethiol –do I get a mug?!

  4. Patt Bowen

    wrote on May 11, 2011 at 2:16 pm

    I love Limburger cheese.even though it is produced by incorporating brevi bacterium linens

  5. alan@benchfly

    wrote on May 11, 2011 at 2:17 pm

    We have a winner!

  6. Leonardo Gedraite

    wrote on May 11, 2011 at 2:20 pm

    Well lets try:
    Gaps: 1- Brevibacteria and 2- methanethiol

  7. Scientists Just Wanna Have Fun (Like Uncaged Monkeys)

    wrote on May 25, 2011 at 11:01 am

    […] Mosquitoes Eating You Alive? Cheesy Feet Could be the Problem. […]

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