They also identified one lucky individual whose unique body odor seemed a little unappealing, opening up a new avenue in finding ways to prevent bites.
Up close, mosquitoes use visual cues and body heat to locate their prey. But when they’re out of visual range — which can be several dozen feet away — they’re thought to track carbon dioxide and other chemicals found in body odor and breath. The precise mixture that most attracts mosquitoes remains part of active research.
Experiments with mosquitoes are usually conducted in relatively small boxes or wind tunnels without the fragrant cacophony of the real outdoors. But such experiments tend to mimic mosquito decision-making too closely. So scientists have built a huge new arena to capture the root of the human-seeking mosquitoes that naturally gravitate to the wild.
“I like to think of this as the world’s biggest perfume for mosquitoes, where they can choose whose scent they like,” said Conor McMeniman, an assistant professor of molecular microbiology and immunology at the Johns Hopkins Malaria Research Institute who led in the study, which was published. in the journal Current Biology.
How do mosquitoes choose their targets?
Mosquitoes are the deadliest human predators, carrying diseases such as malaria, yellow fever and dengue fever that kill more than half a million people each year.
Anopheles gambiae, one of the species that carries malaria, is a particularly dangerous predator. There are different estimates how far the the mosquito fliesbut they tend to cover less than half a mile a day, according to a study from West Africa. They usually feed around midnight, flying into the open corners of people’s homes. In Zambia, 2,000 people die from malaria every year.
To learn how these mosquitoes stalk their sleeping victims, scientists built an outdoor testing arena roughly the size of two tennis courts, or 2,000 times the size of a typical laboratory setup. They let the mosquitoes acclimatize in their open-air laboratory. Then, the researchers did their best to get in the right mood.
At stations scattered around the arena, air conditioning ducts delivered a bouquet of various people sleeping in nearby tents. At each station, piped-in aromas met hot plates that warmed to human body temperature, along with puffs of carbon dioxide.
Using an infrared camera, the scientists watched which hot plates became mosquito discos. They found that heat and carbon dioxide were not enough to attract insects without the added element of human body odor.
“This study adds a lot,” said Leslie Vosshall, a neurobiologist and chief scientific officer of the Howard Hughes Medical Institute whose laboratory recently discovered that skin chemistry determines whether people are magnet magnets. mosquito for another species, Aedes aegypti, which carries yellow fever.
“It’s a different mosquito — it’s a more important mosquito,” Vosshall said of Anopheles gambiae. “This mosquito kills more people … it’s a real apex predator of humans.”
The study found that mosquitoes are particularly attuned to oily secretions that hydrate the skin and protect it from germs. Chemical compounds called carboxylic acids are a strong draw — both in the new study and in Vosshall’s work with Aedes aegpyti.
But one individual in the new study was quite unattractive, the researchers found. Their signature scent includes an unusually low amount of carboxylic acid and high eucalyptol, a substance found in many plants, raising the possibility that diet may play a role, McMeniman said.
What’s next for mosquito researchers?
Now that the researchers have shown that their testing arena works, they are planning a larger experiment in which they will pit 120 sleeping people against each other in rounds of multiple choice competition, to see who the mosquitoes can’t resist. and who is not. .
They hope to determine what combination of chemicals makes one person more attractive than another. They will also study the extent to which factors such as diet or the microorganisms on people’s skin — the skin microbiome — influence their attractiveness. McMenihan also dreams of building a similar facility in the United States to test other mosquito species that spread disease and destroy backyard barbecues.
Insights gained from such experiments could lead to new ways to repel mosquitoes, perhaps by finding ways to alter or hide skin chemistry, making them less attractive to humans. .
But the search for an explanation of why mosquitoes prefer some people over others is likely to run counter to a simple answer. Previous experiments have found that pregnant women are more likely to attract mosquitoes. Drinking alcohol attracts mosquitoes. Using certain types of soap, even those that leave an odor dominated by a chemical known to repel mosquitoes, conversely increases people’s attractiveness to mosquitoes.
“What really matters to the mosquito is not the most abundant type of chemical, it’s really the chemical interactions and relative abundance,” said Clément Vinauger, an assistant professor of biochemistry at Virginia Tech. He recently tested four commonly used soaps and found that three increased people’s attractiveness to Aedes aegypti mosquitoes, while one — Native Coconut and Vanilla body wash — seemed to decrease it, perhaps because mosquitoes dislike coconut oil.
“The short answer,” Vinauger said, “is that it’s a complex problem.”
