CALIFORNIA, U.S.A. – Kim Zarins is adored by mosquitoes. Zarins, a professor of English at Sacramento State University, says the insects have such a strong preference for her that her 20-year-old son enjoys accompanying her outside as she acts as a decoy, and “he knows he’ll be safe.”
However, there is now hope for relief as scientists can identify what attracts these bloodsucking, ravenous mosquitoes with the use of insect magnets like Zarins.
Mosquitoes are more than just a bother; they may spread deadly diseases, including dengue fever, malaria, West Nile disease, and Zika, and they cause more than a million fatalities annually.
Furthermore, mosquitoes that transmit disease-causing organisms have become more widespread as the Earth heats, even reaching areas of the United States like Connecticut, California, and Arizona, despite historically being more common in tropical regions.
To focus on their prey, mosquitoes employ a range of stimuli. Some mosquitoes have developed to seek out our distinct scent because of the way we smell, which sets us apart from other creatures.
They follow the carbon dioxide plumes we exhale with every breath from as far away as 200 feet.
They can smell the scents coming from our skin, underarms, and feet as they get a few feet closer. They start to perceive us as dark outlines against the light at about fifty feet. Lastly, taste receptors on their feet assist them in determining where to bite, and pools of heat direct them to the best landing spots.
“It’s very striking how good mosquitoes are at detecting us,” says Diego Giraldo, a neuroscientist at Johns Hopkins and co-author of a 2023 John Hopkins study that characterises human odour profiles that attract Anopheles gambiae, an African mosquito that transmits malaria.
How does the latest mosquito research differ from the previous one
The new research shows, for the first time, that mosquitoes can discriminate between multiple people in a large, spacious arena the size of an ice-skating rink. Previous studies used much smaller chambers and pitted one person against another.
Eight tents were connected to the arena used in Giraldo’s experiment by air ducts, which directed smells from each tent’s tenant onto a heated, black disc in the experimental area. When mosquitoes landed on each disc, their movements were recorded by infrared cameras.
Mosquitoes were four times more likely to land on the disc belonging to the subject that drew the most mosquitoes during the experiment than they were to land on the subject that attracted the fewest. According to Giraldo, “this just drives home the point that mosquitoes do seem to prefer some people over others, even in complex situations with multiple sources of odour.”
The scientists then used a device that can split the gases that make up the sample into their constituent parts to identify the compounds in each subject’s odour profile. But according to Stephanie Rankin-Turner, a chemist who is currently at the University of Pittsburgh and who contributed to the study, “human odour is incredibly complex.”
“There are a lot of chemical compounds in human odours that no one has ever classified before.” The researchers narrowed the field by concentrating on molecules that are known to contribute to human fragrance.
Their investigation revealed that all of the participants’ odours contained 15 airborne components. However, the likelihood that they would be bitten by a mosquito depended on the quantities of these different compounds. According to Rankin-Turner, “if a compound that mosquitoes truly enjoy is released in large quantities by one individual, that has the potential to increase their attractiveness to mosquitoes.”
How does the skin microbiome play a big role in how humans smell
Carboxylic acids, a family of fatty acids present in human perspiration that have a smell commonly likened to rancid butter or cheese, were particularly attractive to the mosquitoes, supporting previous research showing a similar preference in another mosquito species. These acids are created when the good bacteria that live on the surface of our skin break down our secretions, but they are also produced by us in our sebum, the greasy layer that shields our skin.
Acetoin, which is similarly produced by skin bacteria, also attracted insects. According to Rankin-Turner, “it certainly appears that the skin microbiome is playing a big role in how we smell and how attractive we are to mosquitoes.”
Furthermore, some aspects of our fragrance are very stable, enduring over months or even years, even when other circumstances like pregnancy, illness, or what we eat and drink can affect it. This supports the finding that some people, such as the English professor Zarins, tend to draw mosquitoes.
Matthew DeGennaro, a mosquito geneticist at Florida International University who did not participate in the study, says, “A lot of us in the field want to understand what makes one person more attractive than another because that secret may allow us to make the next generation repellent.”
To better elicit these linkages, he said that the researchers were able to create naturalistic, nearly field-like settings.
