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Buttery-smelling chemical disorients mosquitoes

A chemical cocktail targets the neuron in its brain that helps it sniff out the CO2 we exhale. Tests in Kenya confirm that confused disease-transmitting pests can't find their hosts.
Written by Janet Fang, Contributor

Having just narrowly escaped from a bloodsucking bitefest, also known as summers in DC, I’m pleased to introduce the discovery of several odor molecules that mess with a mosquito’s ability to sniff us out.

Carbon dioxide in our exhaled air is the most important sensory cue used by female mosquitoes to locate a host for their blood-meal.

Their CO2 receptors are located on tiny, antennae-like appendages near their mouths (pictured). Upon encountering a CO2 plume, they orient and fly upwind, eventually landing on us.

Traps that use CO2 are already available, but these are expensive and rarely used in developing countries, where mosquito-borne diseases kill millions.

But by targeting the CO2 detection machinery, scientists have long hoped to disrupt their host-seeking abilities.

A team led by Anandasankar Ray of the University of California, Riverside, examined 3 species of disease-transmitting mosquitoes: Anopheles gambiae (for malaria), Aedes aegypti (for dengue and yellow fever), and Culex quinquefasciatus (for West Nile virus). The 3 combined infect half a billion people a year.

They identified 3 classes of odorants that could keep the mosquitoes away:

  1. Inhibitors: inhibit the CO2 receptor in mosquitoes.
  2. Imitators: mimic CO2 and could be used as lures in traps to attract them away from us.
  3. Blinders: cause ultra-prolonged activation of the CO2-sensing neurons, effectively ‘blinding’ the mosquitoes and disabling their CO2 detection machinery for several minutes.

That blinder class of chemicals includes 2,3-butanedione, which is found in alcohol and added to buttery-flavored food.

The resulting overstimulation tricks the mosquito’s brain into thinking it’s surrounded by huge quantities of gas, so it can’t decide where to go, BBC explains.

Or, as Discover’s Ed Yong puts it, the chemicals cause them to go berserk, firing so wildly that they become useless. By disabling a mosquito’s guidance system, the researchers found a way of making these human-seeking missiles go careening off course.

Then the team tested the effectiveness of a blend of blinders. Even in a wind tunnel, mosquitoes can steer towards CO2, but their ability to do so was disrupted when exposed to the blend.

Then in Kenya, the team release females into a large greenhouse that contained 2 huts (pictured) with CO2-emitting traps in them.

One of the huts also had some ultra-prolonged blend in a small fan-driven dispenser. Only a few mosquitoes entered the CO2 trap in this hut.

“The identification of such odor molecules, which can work even at low concentrations, and are therefore economical, could be enormously effective in compromising the ability of mosquitoes to seek humans,” Ray says.

New lures and repellents based on these findings could replace the bulky, expensive CO2-based models used now. But first, they have to figure out how to control 2,3-butanedione levels… too much of it has been linked to lung disease.

UC Riverside has patents on the discovery, which it has licensed to a new startup, Olfactor Labs. Product prototypes are planned for 2012.

The study was published in Nature yesterday.

Top Image: Olfactory organs of female mosquito, along with electrical recordings from a CO2-sensitive neuron and chemical structures of active compounds / Stephanie Turner
Bottom Image: Ray lab, UC Riverside

This post was originally published on Smartplanet.com

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