When Edward O. Wilson, a champion of conservation and a renowned entomologist, calls for eradicating mosquitoes and is willing to take on the role of an executioner, there must be very little doubt about how dangerous these tiny insects can be. Nearly a million die from diseases carried through mosquito bites every year— 600,000 alone from malaria. To our ever-growing plans to reduce mosquito-borne illnesses, scientists have found a way to prevent mosquitoes from biting us by, quite literally, altering our ‘taste’
A Taste Test
Recently, in a paper published in iScience, scientists explain that certain mosquito species are attracted to, or repelled by, differences in skin odor, chemistry, and bacteria. Scientists believe that by understanding how mosquitoes choose their hosts, they can prevent the spread of mosquito-borne illnesses. They can also assess the risk a demographic faces from mosquitoes and whether manipulating skin chemistry can create new kinds of mosquito repellents.
Mosquitoes rely on visual, thermal, and scent cues to locate their targets. Human scent is a mixture of over a thousand different chemical signatures, many of which are produced by bacteria living on the skin. Determining which specific cues mosquitoes rely on to locate their preferred host is challenging, and for now, much work remains to be done.
Matthew DeGennaro, a neurogeneticist at Florida International University in Miami, and colleagues recruited 119 volunteers and exposed three mosquito species to each person’s scent. For Aedes aegypti and Aedes albopictus, known for dengue fever and chikungunya outbreaks, volunteers placed their arms inside a device designed to let the mosquitoes smell them but not bite. These mosquitoes also feed during the day, unlike Culex quinquefasciatus, which feeds at night. To observe the latter species, each volunteer wore a nylon sleeve for several hours to capture their scent, which the researchers then placed in the apparatus in the dark. For each person or sleeve, the scientists measured how many mosquitoes of each species entered the device to investigate the cues.
Mosquitoes and Their Palate
Each species preferred a different group of volunteers; for example, A. aegypti showed a slight but meaningful preference for males over females. Although some people attracted more than one mosquito species, no single volunteer was attractive to all three species. The team collected samples of volatile compounds in the air around each person’s arm and samples of skin bacteria that may have created some of those compounds. The scientists looked for commonalities among the small cohort who were most and least attractive to each mosquito species, respectively.
A. aegypti and C. quinquefasciatus were more attracted to people with less skin odor, while A. albopictus was attracted to 13 chemicals that had a plant-like odor. However, certain skin bacteria were present in all three attractive groups, including Corynebacterium kefirresdentii, Cutibacterium granulosum, and a strain of Staphylococcus epidermis. However, human odor is complex, so detecting every class of compound that comprises it is nearly impossible. Still, the preferences suggest that each species may have evolved unique methods to find its hosts, most likely based on the types of host each species feeds on and the time of day they seek food.
The scientists plan to study how skin bacteria produce odors that affect a mosquito’s affinity for the host, and use the knowledge to design microbe-based repellents or lures for traps to target the most prevalent mosquito species in a region. “We’re all trying to figure out how to stop people from getting sick,” Kaylee Marrero, a mosquito neurobiologist at Florida International University in Miami, says. “Figuring out why [mosquitoes] are biting people is the best way to do that.”
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