Mosquitoes have more ways to smell us than we thought

Mosquitoes with human-scent receptors removed from their antennae can still smell humans, which suggests their olfactory system has built-in redundancy.

Female mosquitoes rely on the cocktail of smells that humans and other animals emit to detect the blood they need to nourish their eggs. The insects pick up scents through olfactory neurons located primarily on their antennae, which detect and transmit scent information to the brain.

Meg Younger at Boston University in Massachusetts and her colleagues used the gene editing technology CRISPR on female mosquitoes (Aedes aegypti) to inactivate groups of human-odour receptors on the olfactory neurons in their antennae.

The team expected that this would prevent the olfactory neurons from detecting the human scent and relaying this information to the brain. However, when they measured neuronal activity as the mosquitoes were exposed to the smell of humans, they found the insects could still detect the smell. “[This was] the last thing that we expected to find,” says Younger.

They suspected that the odours activated other receptors on the olfactory neurons. To confirm this, the researchers used RNA sequencing to pinpoint what was happening on a cellular level. They found that a single olfactory neuron could possess multiple types of receptors, rather than just one, and that human odour engaged some receptors than hadn’t been inactivated.

“If one of these types of olfactory receptors is mutated or no longer functioning, there’s this backup system,” says Christopher Potter at Johns Hopkins School of Medicine in Maryland who recently found a similar phenomenon in fruit flies (Drosophila melanogaster). “It’s changing the dogma of what we thought we knew about the olfactory system.”

The discovery that mosquitoes are even better at detecting human scents suggests that efforts to prevent the spread of mosquito-borne disease should be differently directed, says Younger. Instead of focusing on gene editing out mosquitoes’ human-scent detectors in the hope they won’t be able to detect people, resources could be channelled into creating more potent traps and repellents, she says.