How to build a scent smorgasbord for mosquitoes
To explore such questions, researchers have often released the insects into small laboratory wind tunnels stocked with used socks or sweat-coated glass beads.
EMILY ANTHES
For a bloodthirsty, global health threat, the African malaria mosquito, Anopheles gambiae, has surprisingly discriminating taste. It prefers feeding on humans to other animals, is more attracted to some people than others and even then appears to have a particular predilection for feet.
“Despite being quite tiny, the African malaria mosquito has a very powerful sense of smell,” Conor McMeniman, a vector biologist at Johns Hopkins University, said. “And it also can be quite choosy.”
Scientists have spent decades trying to decode the chemistry of mosquito attraction, working to identify precisely which odours they are drawn to and why some people are mosquito magnets. To explore such questions, researchers have often released the insects into small laboratory wind tunnels stocked with used socks or sweat-coated glass beads.
But Dr. McMeniman wanted to better replicate the way that the mosquito selects its targets in the real world. “We really wanted to create a spacious sort of home away from home for the Anopheles gambiae mosquito,” he said, “where we compete multiple sources of human odor against each other to see what they like best.”
And so, he and his colleagues built a 4,300-square-foot “flight cage” at the Macha Research Trust, a health research institute in southern Zambia. The structure became the centrepiece of an elaborate experimental system involving sleeping volunteers, customised canvas tents, precisely warmed hot plates and mosquito-tracking cameras.
Although the research is in early stages, the scientists hope that learning more about “the sensory biology of how mosquitoes track and hunt humans” could lead to better mosquito lures and repellents and, ultimately, new strategies for tackling malaria, Dr. McMeniman said.
Here’s how they conducted their first studies, which were published in May in Current Biology. The Macha Research Trust is remote. “Not a backhoe, cement truck or crane within miles,” Chris Book, the institute’s administrative director, said. Local workers mixed the concrete, poured the foundation and erected the steel beams by hand, while a tailoring company sewed together the netting that encloses the structure.
Anopheles gambiae is “the night owl of the mosquito world,” Dr. McMeniman said, so the experiments began in the evening. At 8 p.m., one researcher entered the flight cage with a container of 200 hungry mosquitoes, released the insects and then quickly exited. (The mosquitoes were bred in a lab and did not carry the parasites that cause malaria.)
The scientists tested the same six volunteers against one another for six nights. They found that the mosquitoes were most attracted to a participant who gave off high levels of carboxylic acids, which are produced by skin microbes and sebum, an oily residue secreted by glands in the skin. The volunteer least attractive to the mosquitoes emitted not only low levels of carboxylic acids, but also lots of eucalyptol, a plant-derived compound that is common in a variety of foods and is known to repel mosquitoes.
Anthes is a journalist with NYT©2023
The New York Times
