Scientists Discover What Attracts Mosquitoes--And How to Repel Them

Mosquitoes are some of the most annoying pests known to man. Female mosquitoes attack humans, causing itchy bites; they can even transmit deadly diseases like malaria, dengue fever, West Nile virus and filariasis. Now, scientists have discovered what attracts these insects to us, which could lead to better ways to repel them.

Scientists have long known that female mosquitoes are attracted to us by smelling the carbon dioxide that we exhale. What is less known, though, is what makes them steer away from our breath and toward exposed areas such as ankles and feet. It's possible that scent attracts them, but exactly what are the odors that they detect? In order to find out, the researchers examines mosquitoes a bit more closely.

The mosquito uses its maxillary palp in order to detect carbon dioxide.  The scientists designated the mosquito's CO2 receptor neuron as cpA and decided to see if it could also detect skin odors. This would help explain how mosquitoes are so adept at finding exposed areas.

During the course of their experiments, the researchers devised a novel chemical-based strategy to shut down the activity of cpA in a mosquito. They then tested the mosquito's behavior on human foot odor; a dish of foot odor-laden beads were placed in an experimental wind tunnel. In the end, they found that the mosquito's attraction to the odor was greatly reduced. This indicated that the mosquito used the same receptor for tracking both CO2 and human skin odor.

"It was a real surprise that we found that the mosquito's CO2 receptor neuron, designated cpA, is an extremely sensitive detector of several skin odorants as well and is, in fact, far more sensitive to some of these odor molecules as compared to CO2," said Anandasankar Ray, one of the researchers, in a news release.

The next step involved using a chemical computational method that the researchers developed. With it, the scientists screened nearly half a million compounds and identified thousands of predicted ligands. They then short-listed 138 compounds and eventually were able to zero in on two compounds: ethyl pyruvate and cyclopentanone. While ethyl pyruvate was found to substantially reduce the attraction a mosquito had toward a human, cyclopentanone acted as a powerful lure.

"Such compounds can play a significant role in the control of mosquito-borne diseases and open up very realistic possibilities of developing ways to use simple, natural, affordable and pleasant odors to prevent mosquitoes from finding humans," said Ray in a news release. "Odors that block this dual-receptor for CO2 and skin odor can be used as a way to mask us from mosquitoes. On the other hand, odors that can act as attractants can be used to lure mosquitoes away from us into traps."

The findings are important for developing better strategies for deterring mosquitoes. This could be crucial in areas where these insects are major carriers of disease.

The findings are published in the journal Cell.