Scientists discover how mosquitoes can ‘sniff out’ humans

Whether you opt for repellant, long sleeves or citronella coils, the dreaded drone of a mosquito always seems to find its way back to you.

Now researchers say they have found the mechanism behind the insect's ability to home in on humans.

Humans give off a fragrant cocktail of body odour, heat and carbon dioxide, which varies from person to person and mosquitoes use to locate their next meal. While most animals have a specific set of neurons that detect each type of odour, mosquitoes can pick up on smells via several different pathways, suggests the study, which is published in the science journal Cell.

"We found that there's a real difference in the way mosquitoes encode the odours that they encounter compared to what we've learned from other animals," said Meg Younger, an assistant professor of biology at Boston University and one of the lead authors of the study.

Researchers at the Rockefeller University, in New York, were baffled when mosquitoes were somehow still able to find people to bite after having an entire family of human odour-sensing proteins removed from their genome.

The team then examined odour receptors in the antennae of mosquitoes, which bind to chemicals floating around in the environment and signal to the brain via neurons.

"We assumed that mosquitoes would follow the central dogma of olfaction, which is that only one type of receptor is expressed in each neuron," said Younger. "Instead, what we've seen is that different receptors can respond to different odours in the same neuron."

This means losing one or more receptors does not affect the ability of mosquitoes to pick up on human smells. This backup system could have evolved as a survival mechanism, the researchers say.

"The mosquito Aedes aegypti is specialised to bite humans, and it is believed that they evolved to do that because humans are always close to fresh water and mosquitoes lay their eggs in fresh water. We are basically the perfect meal, so the drive to find humans is extremely strong," said Younger.

Ultimately, the researchers say, understanding how the mosquito brain processes human odour could be used to intervene in biting behaviour and reduce the spread of mosquito-borne diseases, such as malaria, dengue and yellow fever.

"One major strategy for controlling mosquitoes is to attract them to traps to remove them from the biting population. If we could use this knowledge to understand how human odour is represented in the mosquito antennae and brain, we could develop blends that are more attractive to mosquitoes than we are. We could also develop repellants that target those receptors and neurons that detect human odour," said Younger.

Dr Olena Riabinina, from the Insect Neuro Lab at Durham University, who was not involved in the research, said: "We already knew that mosquitoes are hard-wired to bite humans, but this research tells us that their olfactory system is different and more complex than we thought. Interventions based on this new information could be very promising."

Dr Marta Andres Miguel, from University College London, who was also not involved, said: "This is a remarkable discovery not only from a fundamental biology perspective, but also from a disease-control perspective, as it opens new paths for the development of novel tools to control mosquitoes, either to attract them to traps, or to repel them and avoid human biting."