Scientists observe mosquito preferences in Zambia's "largest experimental field". PHOTO CREDIT: JULIEN ADAM

How do mosquitoes find people 100 meters away?

To find out, scientists built an outdoor mosquito experiment the size of an ice skating rink in Zambia. They found that human body odor is crucial for attracting mosquitoes over long distances. The team also found that certain body odor components may explain why some people attract mosquitoes more than others. Related research was published in "Current Biology" on May 19.

Currently, most studies on mosquito preferences are conducted in confined laboratory settings, making it difficult to simulate mosquito behavior in the wild. In order to test how Anopheles gambiae locates and selects human hosts on a larger spatial scale, researchers from the Johns Hopkins University Bloomberg School of Public Health and the Zambia Macha Research Trust collaborated to build a A 1,000-square-meter mosquito experiment field was established.

"This is the largest experimental site in the world to assess mosquito olfactory preferences," said Diego Giraldo, lead author of the paper and Johns Hopkins Bloomberg School of Public Health. A busy sensory environment."

The researchers set up a circle of evenly spaced floor mats in the experimental field, and these mats were heated to the temperature of human skin (35 degrees Celsius). Each night, the researchers released 200 hungry mosquitoes into the experimental field and monitored their activity with infrared motion cameras, recording how often the mosquitoes landed on each pad (a sign that they were preparing to bite).

First, the team compared the importance of temperature, carbon dioxide and human body odor in attracting mosquitoes. They found that mosquitoes were not attracted to the purely heated mat unless the latter was also baited with carbon dioxide, but that human body odor was more attractive than the carbon dioxide bait alone.

Next, the team tested the mosquitoes' selectivity. To do this, they had six people sleep six nights in one-person tents around the arena, and used modified air-conditioning ducts to send air from each tent to heated pads, which contained human body fat. odor. In addition to recording the mosquitoes' preferences, the researchers collected air samples from the tents to characterize and compare the composition of human odor in the air.

"These mosquitoes usually bite humans in the hours around midnight," said corresponding author Conor McMeniman of Johns Hopkins University. Enter the room around two in the morning to bite people. We want to assess the smell preference of mosquitoes during the peak activity period and the smell of people sleeping at the same time." He said that the research results can help scientists design new traps and mosquito repellents , to protect people from deadly mosquito-borne diseases.

The researchers found that, night after night, some people were more attracted to mosquitoes than others, and one of the volunteers, who had a very different scent composition than the others, was rarely bitten by mosquitoes.

The research team identified 40 chemicals that all humans emit, though at different rates. "Mosquitoes may prefer a mixture of specific ratios. We don't yet know which aspect of skin secretions, microbial metabolites or respiratory emissions really influences this, but hopefully we'll be able to figure out the mechanisms in the next few years." Co-first author Stephanie Rankin-Turner of the Johns Hopkins Bloomberg School of Public Health said.

While each person's odor profile varied from night to night, the researchers found some relatively stable patterns: People who were more attractive to mosquitoes consistently released more carboxylic acids, likely produced by skin microbes. In contrast, people who were the least attractive to mosquitoes released fewer carboxylic acids but higher levels of eucalyptol. The researchers speculate that the elevated levels of eucalyptol may be related to diet.

The researchers were surprised by the mosquito's ability to effectively locate and select humans as a food source. "When you see how mosquitoes follow scents to find humans in Zambian fields, you understand how powerful these mosquitoes are," Rankin-Turner said.

(Original title "The largest experimental field reveals the bloodthirsty preferences of mosquitoes to help develop better mosquito repellants")

Related paper information:

http://doi.org/10.1016/j.cub.2023.04.050