Bloodthirsty mosquitoes can smell their prey in more than one way, scientists say

Do you still find yourself covered in bites during the summer, even when you’ve covered yourself in mosquito repellent?

Scientists may have figured out why, because bloodthirsty pests have evolved the ability to detect human body odor in a number of ways.

Most animals smell with “olfactory receptors” in their noses or antennae, which each detect a single, unique odor particle.

The receptors are connected to “olfactory neurons” which relay information about that particular smell to the brain.

However, researchers from Rockefeller University in New York, USA, found that the antennae neurons of mosquitoes are connected to several types of receptors.

This means that their neurons are activated by more than one chemical produced by humans, so if one type of receptor is knocked out, they can still track us down.

Professor Leslie Vosshall, lead author of the study, said: ‘You have to work harder to knock out the mosquitoes because getting rid of just one receptor has no effect.

“Any future attempt to control mosquitoes through repellents or anything else must take into account how unbreakable their attraction to us is.”

Female mosquitoes are able to stalk humans through the carbon dioxide we exhale and chemicals in our body odor, including 1-octen-3-ol and amines (stock image)

Most animals smell with the “olfactory receptors” in their nose (or “maxillary palp”) and antennae, which each detect a single, unique odorous particle. The receptors are connected to “olfactory neurons” which relay information about that particular smell to the brain. Glomeruli are the connections between olfactory neurons and nerves in the brain

Most animals smell with “olfactory receptors” in their noses or antennae, which each detect a single, unique odorous particle, and that’s what mosquitoes would expect.

However, researchers from Rockefeller University in New York, USA, found that the antennae neurons of mosquitoes are connected to several types of receptors. This means that their neurons are activated by more than one chemical produced by humans, so if one type of receptor is knocked out, they can still track us down.

HOW DO MOSQUITOES SMELL IN MAN?

Mosquitoes have olfactory receptors in their antennae which are connected to neurons that transmit olfactory information to their brain.

Each receptor detects a specific olfactory particle, which triggers the neuron to which it is linked.

In most animals, each neuron has receptors that detect the same odorous particle.

However, New York-based researchers have discovered that mosquito neurons have receptors that detect different particles.

This means that the loss of one or more receptors does not affect mosquitoes’ ability to pick up human odors.

Lead author Professor Meg Younger, from Boston University, said: “This project really started unexpectedly when we were looking at how human scent was encoded in mosquito brains.”

Mosquitoes are able to stalk humans through the carbon dioxide we exhale and chemicals in our body odor, including 1-octen-3-ol and amines.

Professor Younger’s team initially used CRISPR gene-editing technology on female mosquitoes, Aedes aegyptito disable clusters of human scent receptors on their antennae.

They expected this to completely stop their olfactory neurons from firing in response to human scent.

However, when they measured neural activity when the mosquitoes were exposed to human scent, they found that the insects could still detect the scent.

The researchers then used RNA sequencing to find out what was happening at the cellular level and found that neurons stimulated by 1-octen-3-ol are also stimulated by amines.

Therefore, the cocktail of chemicals in human smell still managed to activate olfactory neurons via receptors that had not been deactivated.

“This may be a general strategy for insects that rely heavily on their sense of smell,” says Vosshall.

It could also explain why insect repellents that work by blocking a specific olfactory receptor aren’t effective, because their neurons can still be triggered by their other types of receptors.

The researchers used RNA sequencing to find out what happens at the cellular level when mosquitoes detect human scent and found that neurons stimulated by 1-octen-3-ol are also stimulated by amines. Pictured: Mosquito antenna with fluorescently labeled olfactory neurons

The findings, published today in Cell, suggest that gene-editing their human scent detectors is not the most effective way to prevent the spread of mosquito-borne diseases, such as malaria and yellow fever. .  Pictured: A revised odor detection model at Ae.  aegypti based on this study

The findings, published today in Cell, suggest that gene-editing their human scent detectors is not the most effective way to prevent the spread of mosquito-borne diseases, such as malaria and yellow fever. . Pictured: A revised odor detection model in oh egyptian based on this study

This goes against all existing rules about animal scent, suggesting that mosquitoes developed this ability as a failsafe to detect precious human blood.

The findings, published today in Cellsuggest that genetic editing of their human scent detectors is not the most effective way to prevent the spread of mosquito-borne diseases, such as malaria and yellow fever.

Instead, the authors suggest we should focus on creating more powerful traps and repellents that work with how mosquitoes process human scent.

Future research will take a deeper look at why pests evolved multiple receptors on single olfactory neurons.

WHY DO MOSQUITOES BIT SOME PEOPLE AND NOT OTHERS?

About 20% of people are more prone to mosquito bites.

And while scientists haven’t found a cure yet, they do have some ideas as to why insects attack some of us more than others.

Blood group

Certain blood types are more appealing to mosquito taste buds.

Research has shown that people with type O blood – the most common blood type – tend to get bitten twice as much as those with type A. People with type B get bitten somewhere in the middle.

Exercise and Metabolism

Sweating while exercising can also make a person more susceptible to mosquito bites.

Intense exercise causes higher body temperatures and a buildup of lactic acid, which sends delicious signals to insects.

Beer

A glass of cold beer makes you sweat and your body releases ethanol, which may be why mosquitoes like to land on beer drinkers.

skin bacteria

Bacteria levels on human skin can encourage mosquitoes to bite, especially where bacteria congregate like on the ankles and feet.

However, having different types of bacteria on the skin tends to put the insects out.

body odor

Mosquitoes use even the faintest of human body odors when searching for potential victims.

It has been known for some time that female mosquitoes use specific sensors around their mouths to detect the carbon dioxide exhaled by humans and animals.

But a few years ago, researchers at the University of California Riverside discovered that blood-sucking insects also use these same sensors to detect body odor — specifically foot odor.