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

Do you find you still get covered in bites during the summer even when you have covered yourself in mosquito repellent?

Scientists may have figured out why, as it the bloodthirsty pests have evolved the ability to sniff out human body odour in more ways than one.

Most animals smell with the ‘olfactory receptors’ in their nose or antennae, which each detect a single, unique scent particle.

The receptors are connected to ‘olfactory neurons’ that transmit information about that particular odour to the brain.

However, researchers from Rockefeller University in New York, USA, have discovered that the neurons in mosquito antennae are connected to multiple types of receptor. 

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, a senior author of the study, said: ‘You need to work harder to break mosquitoes because getting rid of a single receptor has no effect. 

‘Any future attempts to control mosquitoes by repellents or anything else has to take into account how unbreakable their attraction is to us.’

Lead author Professor Meg Younger, from Boston University, said: ‘This project really started unexpectedly when we were looking at how human odour was encoded in the mosquito brain.’

Mosquitoes are able to track down humans by the carbon dioxide we exhale, and the chemicals in our body odour, including 1-octen-3-ol and amines.

Professor Younger’s team initially used the gene-editing technology CRISPR on female mosquitoes, Aedes aegypti, to deactivate groups of human-odour receptors on their antennae.

They expected this would entirely prevent their olfactory neurons from firing up in response to the human scent.

However, when they measured neuronal activity as the mosquitoes were exposed to human odour, they found the insects could still detect the smell.

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

Therefore, the cocktail of chemicals in human odour was still managing to activate olfactory neurons through receptors that had not been deactivated.

‘This may be a general strategy for insects that depend heavily on their sense of smell,’ says Vosshall. 

It could also explain why insect repellents that work by blocking a specific scent receptor are not effective, as their neurons can still be triggered by their other receptor types.

This goes against all existing rules of how animals smell, suggesting mosquitoes evolved this ability as a fail-safe of sniffing out valuable human blood. 

The findings, published today in Cell, suggest that gene-editing out their human-scent detectors is not the most effective way of preventing the spread of mosquito-borne disease, like malaria and yellow fever.

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

Future research will look more deeply at why the pests have developed multiple receptors on single olfactory neurons.