Bug off! Scientists study how mosquitoes learn to associate your scent with a swat

Mosquito
A mosquito flies on the end of a tether during an experiment to study responses to a swat-like shock. (Kiley Riffell Photo via University of Washington)

Does it do any good to swat at a mosquito if you miss? Yes, according to a newly published study.

A novel experiment conducted primarily by biologists at the University of Washington found that mosquitoes seem to associate the shock of the swat with the swatter’s scent, and learn to stay away.

“Once mosquitoes learned odors in an aversive manner, those odors caused aversive responses on the same order as responses to DEET, which is one of the most effective mosquito repellents,” senior author Jeff Riffell, a UW biology professor, said in a news release. “Moreover, mosquitoes remember the trained odors for days.”

The study, published in Current Biology, was intricately designed to gauge the learning abilities of the mosquito species, Aedes aegypti. First, the mosquitoes were exposed to a variety of scents, taken from a variety of humans as well as rats and chickens. While exposed to some of the scents, the bugs were subjected to mechanical jolts analogous to swatting and shivering.

After the training period, the mosquitoes were put in chambers where they could choose which scent to head toward. They usually went for the scent that wasn’t associated with the swatting sensation. (However, the bugs didn’t seem to be sensitive to chicken scents.)

In another phase of the trial, mosquitoes were glued to a custom-made, 3-D-printed miniature arena, in which they could fly in place while researchers recorded neuronal activity in the olfactory center of their bug brains.

Those neurons were less likely to fire in mosquitoes whose genetic code was tweaked to disable their dopamine response. The researchers say that suggests that dopamine is a critical component for the bugs’ ability to learn scents and associate them with hosts that make better (or worse) targets.

Mosquito arena
A mosquito is held in a custom-built arena for study. (Kiley Riffell Photo via UW)

“By understanding how mosquitoes are making decisions on whom to bite, and how learning influences those behaviors, we can better understand the genes and neuronal bases of the behaviors,” Riffell said. “This could lead to more effective tools for mosquito control.”

That’s a big deal, because Aedes aegypti provides a well-known channel for spreading the Zika virus as well as the viruses associated with yellow fever, dengue and chikungunya.

The research suggests that it’s worth swatting at a mosquito even if you miss, although it might take a while for the mosquito to get the message. For now, chemical repellent is still the most sure-fire way to keep the pests away, but scientists have come up with other scent-based strategies, ranging from eating garlic to swearing off alcohol.

Clement Vinauger and Chloe Lahondere are the lead authors of the study, titled “Modulation of Host Learning in Aedes Aegypti Mosquitoes.” Vinauger and Lahondere are former UW researchers who are now at Virginia Tech. In addition to Vinauger, Lahondere and Riffel, the authors include Gabriella Wolff, Lauren Locke, Jessica Liaw and Jay Parrish from UW, plus UC-Riverside’s Omar Akbari and Caltech’s Michael Dickinson.

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