Why mosquitoes find some of us more attractive than others

Why mosquitoes find some of us more attractive than others

High school is volatile enough without introducing immortality, politics spanning generations, and an endless thirst for blood, but that’s a normal day in vampire academy (now peacock transmission!). When and why a vampire decides to drink a specific person’s blood could have a complicated set of motivations, but if vampires are like our own real-world bloodsuckers, they may seek out some people more than others.

People have long speculated about what might attract or repel mosquitoes. Some suggest that eating certain foods makes you more or less attractive, while others think that gender or age contribute to how tasty mosquitoes find you. It is a matter not only of comfort, but also of public health. Mosquito bites are annoying, but can also be debilitating or deadly. According to a recent study published in the magazine Cellcertain individuals can be more than a hundred times more attractive to mosquitoes than others, and now we can see why.

Dr. María Elena De Obaldia led the study during her postdoctoral fellowship at the Rockefeller University Neurogenetics and Behavior Laboratory. They collected odor data from dozens of people over the years and used those samples to identify what rings the mosquito’s dinner bell. Picking up a person’s scent may seem like an impossible problem, but there was a relatively simple and obvious solution. If she’s ever picked up a friend or family member’s shirt and smelled its signature scent, she’s already most of the way there. The scientists had study participants wear nylon stockings on their arms six hours a day for several days.

“This was something we asked people to do hundreds of times. Then the nylons could be frozen so we could be flexible about when to wear them. We would then take the stockings and cut them into index-size pieces. That would then be put into the behavioral assay and used as mosquito bait,” De Obaldia told SYFY WIRE.

DNA of Cassidy and mosquito GETTY

All identifying information was removed from those samples, so the researchers didn’t know who had used a particular piece of nylon, but they could identify the samples by number. Very quickly, certain numbered samples began to stand out. Subject 33, for example, was more than four times more attractive than the second most popular sample and more than 100 times more attractive than the least attractive sample. This suggests that something about our scent dictates, at least to some extent, how voraciously a mosquito will pursue a particular target.

“Once we understood which ones were the most or the least attractive, we used the same method to collect the odor and analyze it chemically,” De Obaldia said. That chemical analysis revealed about 50 chemical compounds that appear to be a major factor in how delicious a person is. Those samples that were highly attractive had higher levels of carboxylic acids than those that were less attractive.

“We think that is an important part of this. We found that people who were more attractive to mosquitoes had much more of these acids in their nylon stockings. We also had some clues because our lab and other labs have been able to make mutant mosquitoes with defects in their sense of smell,” De Obaldia said.

Use of CRISPR for editing the mosquito genome, the researchers produced mutants incapable of sensing these acids and were considerably compromised in their attraction to human scent. That confirmed that carboxylic acid is probably a big part of what makes you attractive to mosquitoes, but it also revealed that the human-mosquito relationship is more complicated than we thought. While the mutant mosquitoes had a harder time spotting a potential blood meal than their unaltered counterparts, they were still able to distinguish between highly attractive and less attractive people.

To understand what is going on here, we imagine ourselves blindfolded while standing in front of a stove. In front of you, on the stove, are two pots. One is filled with a watery broth while the other is filled with a rich stew. Your sense of smell definitely tells you which is which, and you’re much more likely to gravitate towards stew. Maybe even a hundred times more likely. So your sense of smell is eliminated, not completely, but quite significantly. Maybe you have a cold or a sinus infection and you are blocked. Your ability to detect broth or stew is compromised. You are not receiving all the signals that you normally would. You might even be eating less because you find it hard to find the kitchen without the scents guiding you. But you can still tell the difference between broth and stew, even if both have been turned off. That seems to be what is happening with the mosquitoes. We can successfully remove some of their scent receptors, but if you’re a mosquito magnet, they’ll come for you.

At the moment, there is little you can do about it. Over the course of the study, the scientists observed that people who were mosquito magnets remained mosquito magnets. Carboxylic acid production levels remained stable over long periods of time, suggesting that it is the result of something genetic or something in the skin microbiome. It’s not clear if there’s anything we can do to change those cues and turn someone very attractive to mosquitoes into some kind of insect idiot. That said, the researchers are hopeful that continued research may reveal state-of-the-art mosquito repellents.

“We found at least one person who, from his chemistry, seemed like he should be a mosquito magnet, but he wasn’t. That shows that we clearly do not understand everything. There may be multiple ways to be a mosquito magnet and there may be other compounds that we haven’t identified yet that break down these super attractors. It would be great to understand why that person was not a magnet for mosquitoes,” De Obaldia said.

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