Mosquitoes Have a Weird, Enhanced Sense of Smell – Futurity

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A new study describes the unique and previously unknown way Aedes aegypti Mosquitoes process odor at a biological level to find humans and bite.

The findings are a departure from core theories that previously guided our understanding of insect olfaction.

If you’ve ever sprayed yourself head to toe with bug spray, and still felt like a mosquito magnet, it won’t surprise you to learn that mosquitoes are really, really good at finding humans to bite. A key factor in this superpower is his keen sense of smell, which is based on the olfactory system.

“Mosquitoes are highly specialized,” says Meg Younger, an assistant professor of biology at Boston University who studies mosquito olfaction. These relentless, buzzing creatures are designed to find us, bite us, use proteins in our blood to reproduce and repeat.

Mosquitoes: Not Just a Seasonal Nuisance

Mosquitoes, as much as they feel like a seasonal nuisance in the northeastern US, are deadly creatures that kill more people than any other animal in the world. Depending on where they live, certain types of mosquitoes carry diseases such as malaria, West Nile virus, Zika virus, dengue fever, eastern equine encephalitis, and others. And hotter, drier, tropical climates fight mosquitoes year-round.

As reported in the newspaper CellYounger is working to crack the code on how mosquitoes use their sense of smell to track us down and better understand how we can most effectively repel them.

Aedes aegypti The mosquitoes normally inhabit hot, tropical climates and have caused minor outbreaks of dengue fever in southern states like Florida and Texas. But in recent years, they’ve been spotted as far north as Connecticut, sounding alarm bells about what to expect as global temperatures continue to warm.

“This is part of why this work is going to become increasingly important,” says Younger, who began the study while completing postdoctoral research with Leslie B. Vosshall at Rockefeller University.

“This is surprisingly strange. It’s not what we expected.”

For humans, odors are registered in the brain through a communication stream that begins in the nose, which is lined with special cells called olfactory sensory neurons. These neurons, which house sensory receptors, specialized molecules that are stimulated by odor particles, act as odor detectors and as messengers to the brain.

“The central dogma in smell is that the sensory neurons, to us in our nose, each express one type of olfactory receptor,” says Younger.

This is the underlying organizing principle of smell: one receptor for one neuron. For example, the smell of a freshly baked apple pie is actually a chemical code created by different odor molecules. As the distinctive odor reaches our noses, it triggers sensory receptors that match the different odor molecules; The corresponding neurons then communicate with a region of the brain called the olfactory bulb, or the lobe of the antenna in insects, where it maps the code of smell.

mosquitoes and human odor

According to the study findings, Aedes aegypti The mosquito olfactory system is organized very differently, with multiple sensory receptors housed within one neuron, a process called gene co-expression. This exceptionally specialized olfactory system could help explain why mosquitoes are so good at sniffing out humans and biting them.

“This is surprisingly strange,” says Younger, who initially thought his observation of mosquito sensory neurons would prove that it’s like any other olfactory system, such as in flies and mice. The difference may sound technical, but it suggests that mosquitoes’ sense of smell is highly in tune with that of humans. “It’s not what we expected,” she says.

Previous research has found that even complete removal of the receptors in mosquitoes that are used to decode carbon dioxide, an important chemical signal they use to hunt humans, does not interfere with their search for people. Younger’s latest study may point to one reason.

In his lab, Younger breeds mosquitoes in incubators and uses modern genetic tools to understand smell in ways that weren’t possible a decade ago.

For this study, the researchers developed mosquitoes that would light up under the microscope when exposed to certain odors; they expressed fluorescent proteins that glow under the microscope, allowing the researchers to see chemical responses to odors. They also used CRISPR technology (which stands for Clustered Regularly Interspaced Short Palindromic Repeats and is a genetic tool created to edit DNA in living organisms) to tag different groups of sensory neurons, preserving the function of cellular proteins.

All the results point to an olfactory system that is unconventional in the way it co-expresses sensory receptors within individual sensory neurons. This suggests a redundancy in the human scent code, and possibly a stronger sense of smell that draws mosquitoes to humans. The next step is to find out what role co-expression plays in driving the behaviors of Aedes aegypti mosquitoes

“One compelling idea is that it makes them good at finding people,” says Younger. Their long-term goal is to intervene in mosquito bites by generating new and improved repellents, or attractants, that are more attractive to mosquitoes than human blood. “As we learn how odor is encoded in your olfactory system, we can create compounds that are more effective based on your biology,” she says.

Until then, Younger uses insect repellant (brands with 15 to 25% DEET or picaridin tend to be rated the most effective) to protect against mosquitoes outdoors. Eventually, with more and more research, she hopes there will be a better option.

Source: Boston University

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