Getting eaten by mozzies? It could be the way you smell

This year scientists revealed why mosquitoes prey on some people but not others – it’s because of body odour.

In an elaborate experiment, researchers from the US and Zambia constructed a 20m-square ‘flight cage arena’, into which they released 200 hungry mosquitoes, and tracked their activity using infrared cameras, publishing their results in Current Biology.

While the experiment involved a handful of willing humans as bait, the researchers are planning a larger-scale experiment involving more than 100 people.

1. Mosquitoes are attracted to human body odour

Mosquitoes use a range of sensory cues to identify their targets, including visual as well as body heat, odour, carbon dioxide and moisture. These cues have different spatial ranges – warmth reaches up to 50cm, visual cues between 5 – 15m with carbon dioxide and body odour potentially stretching as far as 60m.

In the experiment, landing pads at the perimeter of the flight arena were baited with carbon dioxide (CO₂), human body odour, or real people sleeping in tents. 

The researchers found human body odour was more attractive to mozzies than CO₂ alone.

2. Mozzies prefer some people’s smells over others

As well as recording mosquito preferences, the researchers collected nightly air samples from people sleeping in tents to characterize and compare 40 different chemical components of individual body odour.

According to the results, mosquitoes were more attracted to body odours containing higher levels of carboxylic acids (likely produced by skin microbes), over those with lower levels of carboxylic acids and elevated levels of eucalyptol (potentially related to a person’s diet).

Eucalyptol – a chemical likely derived from plant-based foods and flavourings in a person’s diet – was highly abundant in the body odour of the least preferred human subject in the six-person cohort. 

3. Mosquitoes are effective hunters, and picky eaters

The researchers were surprised by how effectively the mosquitoes could locate and choose between potential human meals within the huge arena. 

“When you see something moved from a tiny laboratory space where the odours are right there, and the mosquitoes are still finding them in this big open space out in a field in Zambia, it really drives home just how powerful these mosquitoes are as host seekers,” says author and analytical chemist Stephanie Rankin-Turner.

4. Mosquitoes hunt humans in the middle of the night 

“Mosquitoes typically hunt humans in the hours before and after midnight,” says author Conor McMeniman, an assistant professor at Johns Hopkins Bloomberg School of Public Health and Johns Hopkins Malaria Research Institute. 

“They follow scent trails and convective currents emanating from humans, and typically they’ll enter homes and bite between around 10pm and 2am. We wanted to assess mosquito olfactory preferences during the peak period of activity when they’re out and about and active and also assess the odour from sleeping humans during that same time window.”

The researchers are hoping to conduct a larger-scale version of their field experiment, with 100 to 120 humans in coming years.

“This work is being coupled in my laboratory with a higher-detail understanding of what we call the human volatile, which is all of the chemical emissions emitted by the human body, says McMeniman when speaking to Johns Hopkins University news team.

“We hope that by characterising variability in the scent signature between humans, we can gain a high-resolution understanding of how we smell as humans and why we’re so attractive to various bloodsucking insects.”

They also plan to genome-engineer mosquitoes to help them understand what neurons are responding to these chemicals.