For many of us, mosquitoes are mostly a source of irritation and annoyance – and if that’s all they are to you, you might count yourself lucky.
That’s because the mosquito is actually the world’s deadliest animal, thanks to its unrivaled ability to spread a swathe of harmful diseases, including malaria, dengue fever, West Nile virus, and more.
It’s estimated that over 1 million human deaths result from this vector every year, so understanding why and how mosquitoes seek us out is a hugely important field of science.
In a new study reported in iScience, we just got a step closer to solving the mystery and figuring out why mosquitoes seem to be strangely more attracted to some people, while ignoring others.
In an experiment led by scientists from Florida International University (FIU), researchers recruited 119 volunteers from Miami and had each of them place their arm in a long tube called an olfactometer.
At the other end of this tube, the researchers introduced three different species of mosquitoes – Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus – to see which mosquitoes were attracted to which people.
We already know that mosquitoes are attracted to human scents – among lots of other unwitting signals – but understanding why subtle differences in body odor affect mosquito attraction has so far remained hard to pin down.
Partly that’s because of the complicated makeup of human body odor itself, formed as odorless secretions on our skin turn into gases called volatile organic compounds (VOCs) through interactions with bacteria in our skin microbiome.
There are thought to be over 1,000 human skin VOCs, many of which warrant further study, so it’s difficult to know exactly how these chemicals relate to specific smells.
And that’s before you consider there are about 3,600 known species of mosquito, each of which has likely evolved slightly different scent preferences, so there’s still a lot we have to learn about how mosquito scent attraction works.
“It has become increasingly clear that there is a connection between human skin microbes and/or odors when mosquitoes target individual humans,” the research team, led by senior author and neurogeneticist Matthew DeGennaro from FIU, explains in their paper.
“Although previous studies have compared the attraction of different mosquito species with individuals, cross-comparing attraction rates of multiple mosquito species to individual human volatilomes and skin microbiomes, to our knowledge, has not been previously accomplished.”
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>In their olfactometer experiment, DeGennaro’s team found the species Ae. aegypti showed slightly higher attraction for males over females, but the other two species tested didn’t seem to show a preference.
The researchers also discovered individual participants seemed to be more attractive to certain mosquito species, but that didn’t mean they were consistently more attractive to all three species.
Similarly, some of the volunteers appeared to offer low-attraction to one (or more) mosquito species, but they weren’t consistently low-attraction for all three kinds in the experiment.
There were weak correlations between the individuals Ae. aegypti and Ae. albopictus were attracted to, but overall, the researchers say each mosquito species appeared to prefer a different cohort of individuals.
In terms of VOCs – sampled from the participants’ arms – the researchers found Ae. aegypti and Cx. quinquefasciatus seemed to be attracted to individuals who had low levels of volatiles associated with low attraction, suggesting they might be avoiding certain VOCs when they decide who to land on.
By contrast, Ae. albopictus appeared to zero in on certain attractive odor compounds.
In total, the researchers identified 246 distinct bacterial taxa across all 119 participants, but the team was surprised to see the microbiomes of all the participants shared only one species of bacteria.
While each mosquito displayed a range of preference differences for the kinds of bacteria they seemed to be attracted to, ultimately, the results showed three specific kinds of bacteria were consistently popular.
Related: Mosquitoes Are Feeding on Us More Often – And Scientists Say We’re to Blame
“Across Ae. aegypti, Ae. albopictus, and Cx. quinquefasciatus mosquitoes, we detected three core bacteria in common for high-attraction participants that were not found across the low-attraction core microbiomes,” the study authors explain.
“These bacterial taxa, Co. kefirresidentii, Cu. granulosum, and Staphylococcus epidermidis, may broadly signal to mosquitoes the presence of an attractive host.”
There’s still a huge amount more to learn about what kinds of odor compounds and bacteria contribute to mosquito attraction, but with each insight, it gets us closer to figuring out how to diminish the threat of mosquitoes.
For example, we might be able to create special kinds of insect repellents that deter mosquitoes, or even engineer our skin microbiome to make ourselves less attractive.
The findings are reported in iScience.
This article was fact-checked by Rachel Garner and edited by Michael Irving. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
