Could we alter mosquitos’ internal clocks to stop them from biting?

People who live in the tropical areas where Aedes aegypti mosquitoes reside have probably known for centuries, or even millennia–thanks to their itchy bites–that the mosquitoes hunt most often at dawn and dusk.

A new study offers scientific proof of that hunting behavior, and new insight into the biological mechanism behind it. It also offers a potential path to reducing bites and helping stop the spread of deadly, mosquito-borne disease.

“The more we can understand about how these behaviors that are so important for pathogen transmission are regulated, the more we can broaden our arsenal of tools that we can use against these mosquitoes,” said Laura Duvall, an assistant professor of Biological Sciences, who led the new study, published this week in the journal Proceedings of the National Academy of Sciences.

The research focuses on Aedes aegypti, a type of mosquito that lives primarily in tropical areas, and that can carry diseases like dengue, chikungunya, and Zika. Although this mosquito species cannot survive harsh winters like those in New York, in recent years they have made their habitats in new areas as climate change enables them to thrive in more temperate climates.

There are many reasons people could, in theory, get more bites from these mosquitoes at dawn and dusk, Duvall said. It could be that they’re just outside more, or that humans are more attractive to them at these times. Her study focused on understanding if this biting pattern is also influenced by mosquitoes’ own daily rhythm.

The research team began by video recording mosquitoes, and watching how they responded to carbon dioxide, a signal mosquitoes use to locate humans. The team used machine learning to quantify the mosquitoes’ movements.

They found that the mosquitoes had a more persistent response to the same amount of carbon dioxide at dawn and dusk, exactly the times of day that many people (both mosquito researchers and not) have reported getting more bites. “This is consistent with the idea that they’re actually better predators at that time of day,” Duvall said.

Suspecting that what was changing was not the mosquitoes’ ability to sense us at these times of day, but the persistence, or aggressiveness, of their response, Duvall’s team used CRISPR-Cas9, a gene editing tool, to mutate a gene that controls mosquitoes’ internal clocks. They found that mutating the gene changed their behavioral timing, making the mosquitoes less persistently responsive to carbon dioxide in the morning. Normally, biting rates are high in the mornings, but when they disrupted the clock gene, the mutant mosquitoes were less successful at feeding during that time.

“This is the first time we’ve found that there’s an internal rhythm in the mosquito’s behavior that could be driving these bites at dawn and dusk. Their internal clocks make them more persistent and predatory in their response to humans at these times of day,” Duvall said.

The findings aren’t immediately commercially viable, and that wasn’t the lab’s goal, Duvall said. But as science begins to understand more about what makes these animals particularly efficient at finding people at specific times of day, she said that “we could, in theory, find ways to lock mosquitoes in a state that prevents them from effectively seeking out humans.” Which could mean fewer uncomfortable bites, and less disease.