Building A Better Mosquito Repellent, By Blocking Their Ability To Smell Us

  @rpalmerscience on December 05 2013 1:54 PM

California scientists think they’ve found a new weapon in the war on mosquitoes: hitting them where they sniff us out. Their discovery might lead to rum raisin-scented bug sprays that mask you from mosquitoes, and mint-scented traps that lure them far away from you.

Mosquitoes employ a two-staged targeting system in their quest to suck our blood. First, they follow the trail of carbon dioxide in our exhaled breaths back to us; then, when they get closer, they zero in on our exposed, tempting flesh by sniffing out the odors of our skin. And we smell pretty good to them; scientists know that, even without the presence of carbon dioxide, a mosquito will still zoom toward the smell of human skin wherever it lingers – unwashed laundry, bedding, even smelly socks.

Scientists have long wondered how exactly the mosquito is attracted to skin scents alone. Pinpointing a receptor in the mosquito that’s key to its skin-sniffing ability could allow researchers to work backwards and find compounds that would block that receptor.

In a paper published Thursday in the journal Cell, a team led by University of California Riverside researcher Anandasankar Ray says it's found an important piece of the puzzle. It turns out that an olfactory neuron in one of the mosquito’s scent-detecting mouthparts called cpA, already known to be a detector of carbon dioxide, is also extremely sensitive to the compounds found in human skin odors.

“Finding out that same [carbon dioxide] receptor is a primary channel for detecting skin odor as well, that makes it a much simpler target,” Ray said in a phone interview.

Blocking cpA could be a great way to keep yourself bite-free, but there’s another potential way to act on Ray’s finding. Creating traps that mimic the scent of human skin could be a much cheaper alternative to the lures currently in use.

“Most [existing] solutions burn propane, or use dry ice evaporation to create carbon dioxide to attract mosquitos,” Ray says. “Now that we have an odor that can activate [this neuron], we can find a nice-smelling compound that can lure mosquitoes effectively.”

Traps can be useful to corral mosquitoes away from your backyard barbeque and to collect mosquitoes for scientific research. Ray thinks his find is the first step to introducing widespread use of mosquito trapping in developing countries throughout the world.

Mosquito surveillance is nearly nonexistent in certain parts of Africa and Asia – ironically, some of the places most seriously  impacted by mosquito-borne illnesses -- “because it’s impossible to get your hands on some dry ice or a butane tank” to fuel current mosquito lures, Ray says.

Ray’s team, using a chemical computational method that screens a database of compounds, has already identified several candidate chemicals that can block or activate the mosquito’s skin-sensing ability. (They used a similar method to look for cheaper effective alternatives to the insect repellent DEET.)

And the candidates don’t smell like sweaty socks, either: ethyl pyruvate, a rum raisin-flavored compound, inhibits cpA activity, while minty-scented cyclopentanone turns out to be a powerful mosquito lure. Both are already approved for use with people (though the U.S. Environmental Protection Agency will probably want to scrutinize them before they can be used in sprays). Ray’s team already has a commercialization partner in place, and expects the development work to progress fairly rapidly.

“We’re coopting compounds used in food flavoring for protecting us,” Ray says.

SOURCE: Tauxe et al. “Targeting a Dual Detector of Skin and CO2 to Modify Mosquito Host Seeking.” Cell published online 5 December 2013.

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