Geneticists get closer to knowing how mosquitoes sniff out our sweat

Geneticists have found a scent-sniffer protein in the antennae of a mosquito. The protein is called IR8a. If that protein could be jammed, it might leave a bloodsucker confused about whether we’re human enough to bite.

Aedes aegypti is one of many mosquito species. It prefers human blood to that of other animals. The bad news: This mosquito can spread Zika and dengue. Those are two dangerous diseases.

Our skin and the many types of microbes that live on the outside of us shed lots of lactic acid. That acid makes up an unusually big part of the human scent, notes Matthew DeGennaro. He’s a geneticist who works at Florida International University in Miami.

Since the 1960s, researchers have mused that lactic acid might be one clue that Aedes aegypti uses to pick out humans. His team’s tests now show that these mosquitoes need IR8a to smell lactic acid.

The researchers worked with Aedes aegypti that make the proper IR8a. They also worked with some of these mosquitoes that make an altered form of IR8a. It doesn’t work properly. All of the insects were offered an alluring human arm or sweat-stained sleeve. Mosquitoes with the altered IR8a were only about half as likely to land on the skin or sweaty fabric as the normal insects. DeGennaro and his colleagues shared their findings March 27 in Current Biology.

The insect system for detecting odors is “very complex,” DeGennaro says. Mosquitoes rely on three families of odor-sniffing proteins. These proteins have overlapping abilities to identify chemicals in the air.

IR8a is a protein that targets acids, among other compounds. As a mosquito hunts, it mixes cues about floating chemicals with other information. These include heat, moisture and the sight of something biteable. A bloodsucker also notices the carbon dioxide we exhale. DeGennaro calls that “mosquito coffee.” It revs the insects up to get to work seeking a meal.