October 6, 2022

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When it comes to sniffing people, mosquitoes always have a Plan B (or C)

When it comes to sniffing people, mosquitoes always have a Plan B (or C)

You cannot get rid of these biting insects.

Nothing is more annoying than a bumblebee mosquito that flies before it falls asleep. And yes, this mosquito also knows where to find you in the dark. Mosquitoes are attracted to the unique combination of body odors they emit. By the way, the researchers explained that it is not so easy to stop this characteristic of mosquitoes. Because even if you remove the receptors that a mosquito smells of us, it will still find a way to track us down.

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In most animals, the olfactory neuron is only responsible for detecting a specific smell. “When people lose a single smell receptor, all the neurons expressing that receptor lose the ability to smell that smell,” researcher Leslie Foshall explains. But she and her colleagues have found, surprisingly, that this is not the case with mosquitoes.

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As mentioned, mosquitoes are attracted to our body odor. This scent stimulates receptors in the two feather-like antennas that mosquitoes provide. Scientists have attempted to remove these receptors in an effort to make humans undetectable to biting insects. But it turned out that it was not so easy. Even after researchers removed an entire family of scent-sensitive receptors from the mosquito genome, mosquitoes found a way to smell humans. “Mosquitoes break all known rules about how to smell things to animals,” researcher Margot Hare said.

Picture of a mosquito antenna. Green represents olfactory neurons. Photo: Margo Hair

To better understand this, researchers studied how human odor is processed in the mosquito’s brain. The fact that mosquitoes are so attracted to us is due to a specific pleasant-smelling substance that lives in our sweat and breath: 1-octen-3-ol, also called octenol. And now it turns out that octinol-stimulated neurons are also stimulated by amines — another chemical that mosquitoes use to track humans. This means that individual neurons express multiple chemical receptors, causing them to function even if one of the receptor families is affected. This way, mosquitoes always have a backup plan to track people down.

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In short, the mosquito’s olfactory system is organized quite differently, with multiple sensory receptors in a single neuron. This mechanism is great, though. She points out that mosquito octenol neurons can also apparently detect amines, something they had never before seen in an animal. “Surprisingly, the neurons that mosquitoes use to detect octinol and amine receptors are not separate parts,” study researcher Meg Younger concluded. “This allows all scents related to humans to activate the human-detecting part of the mosquito’s brain, even if some receptors are lost.”

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Essentially, mosquitoes have developed certain mechanisms in their olfactory system that allow them to always smell our scents. “You can’t get rid of mosquitoes,” Foshall says. “Future attempts to control mosquitoes with mosquito repellents will take into account their attraction to us.”

The mosquito may not be the only animal that has found a way to outsmart us. Fossall thinks other insects have a similar mechanism. For example, previous research has shown that Drosophila have the same co-expression of the receptors in their neurons. “This could be a general strategy for insects that rely heavily on their sense of smell,” Foshall suggests. The researchers plan to further study the functional significance of the co-expression of different types of olfactory receptors in future work.