Tuesday, June 14, 2011

How Mosquitoes Smell You

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Mosquitoes had been thriving on Bull Creek as frequent rains left lots of little breeding spots.  While they use their piercing mouths to obtain nectar and plant juices, the adult female needs just a little of blood before she can produce eggs.  Some species like my blood.

How do they find me up on the deck?  They use specialized maxillary palps near their mouths to sense carbon dioxide, then hone in on the source.  Since holding my breath outside isn't an option, we are left with chemical repellents.  Citronella candles are effective if you are close to their smoke.  A variety of folk remedies and natural compounds may help but aren't as effective as DEET.  Treating clothes with permethrin is effective and withstands multiple washings and some clothes come pretreated.

New research in the Journal Nature describes three types of new chemicals that can confuse those same sensory palps that are looking for carbon dioxide.  They were discovered while studying fruit flies which also seek out carbon dioxide, in this case produced by ripe fruit.  Some of these fruits have developed chemicals which block those receptors.  Studying these molecules with mosquitoes, Anandasankar Ray, of the University of California, Riverside, says  they seem to work three different ways.  Quoting from a story on livescience.com,
  1. The first group works by binding to the mosquitoes' carbon dioxide receptors in the maxillary palps, stopping the mosquitoes from sending the signal indicating there's a mammal close by when they sense carbon dioxide.
  2. The second group of molecules acts to mimic carbon dioxide's effect on the mosquito they turn on the carbon dioxide sensing neurons and essentially overwhelm them.
  3. Another group of odor molecules essentially blinds the mosquito to any nearby blood-filled humans by disabling their carbon dioxide-detection machinery. Even a brief exposure to these molecules was enough to confuse the mosquitoes' carbon-dioxide detectors for minutes and severely reduced their sensitivity for minutes afterward.
They found the maximum effect was achieved by mixing the different chemicals.  With this mixture the mosquitoes couldn't find the carbon dioxide trail either in the lab or in the field.   Human studies are underway.  Someday we may not have to apply the oily DEET mixtures.

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