Mosquitoes can be among the deadliest animals for humans because of all their buzzing and biting and annoying, as well as transmitting different viruses and parasites they carry. Some species of these flies feed exclusively on humans, but to be such a successful feeder they must have developed precise targeting mechanisms to distinguish between human and animal odor. Researchers are trying to understand how they make this distinction, and a new study published in Nature aims to answer the question of what and how mosquitoes detect.
Carolyn “Lindy” McBride, assistant professor of ecology, evolutionary biology and neuroscience, said in a statement: “We kind of dived into the mosquito brain and said, ‘What can you smell? What triggers your brain? What activates your neurons? And when you smell animal versus human smell, your brain How is it activated differently?’ we asked,” he said.
Using CRISPR-Cas9, the team created genetically modified Aedes aegypti mosquitoes that are vectors of Zika virus, dengue virus, yellow fever virus and chikungunya virus. These transgenic insects had brains that glowed when active, allowing scientists to image the brains in high resolution. The researchers then fed the mosquitoes in question human and animal flavored air through a wind tunnel to determine what attracted the insect.
Human odor is made up of many different components, and these same components are present in different proportions in most mammalian odors. Precisely determining attractive component ratios was another challenge, as past research has found that the ingredients by themselves are not attractive to mosquitoes.
The team used the scents of 16 humans, two rats, two sheep, two quails and four dogs to induce mosquito appetite. The way they collected these samples was also quite interesting. For the sheep, there was a farm that donated a few pelts, and for the dogs they visited a grooming parlor and collected trimmed hairs.
The method used for humans was more interesting. “We had a lot of wonderful volunteers for the human samples,” said study author Jessica Zung. “We asked them not to shower for a few days, then undress and lie down in a Teflon bag.”
The reason why the volunteers were required to be naked was that the clothes could spoil the human odor.
After collecting all these odors, they designed a smart system to blow odors on genetically modified mosquitoes in the imaging setup area. The mosquito brain has 60 nerve centers called glomeruli, and the team initially assumed that many of these centers would help mosquitoes find their next meal and distinguish human scents from animals, but it turned out to be the opposite.
Research team member Zhilei Zhao said, “When I first saw the brain activity, I couldn’t believe it – only two glomeruli were involved,” said. I repeated it over and over. I absolutely couldn’t believe it. It’s so simple.”
Experiments determined that mosquitoes detect two chemicals (decanal and undecanal) that are rich in human odor and likely originate from unique human skin lipids rather than sweat.
Overall, this exciting collaborative research could help develop new repellents and protect us from mosquito bites much more effectively.