Mosquitoes learn to avoid people who’ve swatted at them

New research shows mosquitoes can recognize their targets’ scents and decide whom to bite.

Mosquitoes don’t decide whom to bite at random, decidedly preferring some people over others. But it’s not clear how exactly they choose where their next meal will come from. Now, new research suggests the insects’ ability to associate the smell of a specific human with the vibration of a swat may be a factor. We spoke with study author Jeff Riffell, a biologist at the University of Washington, to learn more.

ResearchGate: What motivated this study?

Jeff Riffell: Mosquitoes are intense vectors of disease, such as West Nile, chikungunya, and Zika viruses. They have the ability to target specific individuals and can easily change their host preferences. Much of the spread of disease is caused by relatively few people. In fact, 80 percent of disease transmission is caused by 20 percent of the host population.

The mosquito’s ability to learn to recognize its targets could be one explanation for how mosquitoes select certain individuals over others. It was thought that the mosquito could learn and remember the smell of an animal that disturbs its bite, and avoid it thereafter. So we wanted to see if Aedes aegypti mosquitoes could learn host cues, and how they accomplish this feat.

This photograph shows a tethered flying Aedes aegypti mosquito. Credit: Kiley Riffell.

RG: What did you find?

Riffell: We found that mosquitoes were able to learn to avoid attractive people, once they learned the association between vibrations simulating a swat and the odor of the person. At these relatively low levels, the vibrations do not cause any stress or physical damage to the mosquito, but it causes the mosquitoes to readily learn the association between that vibration and an odor. Once learned, the aversive responses were similar to how mosquitoes react to DEET, currently one of the most effective mosquito repellents!

We also looked at whether mosquitoes could learn to bite other, non-typical hosts, like a bird or rat. We found that they could learn the rat odor, but they couldn't learn the bird odor. Aedes aegypti bite mammals, so perhaps this wasn't surprising. But it did show that mosquitoes could learn other odors.

RG: Does this mean if I swat at a mosquito in my backyard, it will leave me alone?

Riffell: If you are the only person in the backyard, there's a chance that the mosquito is so desperate that it might go back and try again. However, if there's another attractive person there with you, then they'll probably go try and bite that other individual, avoiding you. So in these types of situations, after shooing away the mosquito, encourage your friend to talk a lot (and thus breath out CO2). That should do the trick.

RG: What role does dopamine play in mosquito learning?

Riffell: Dopamine is a critical chemical for learning and motivation in animals ranging from humans to honeybees. We found that genetically modified mosquitoes that lacked functional dopamine receptors could no longer learn. We next recorded neurons in the olfactory center of the mosquito brain, and found that without dopamine, neurons were less likely to react to specific host odors.

These two experiments showed us that influencing dopamine in the mosquito brain can suppress the mosquito's ability to learn, while also decreasing its ability to process odor information.

RG: How do you hope this research will be used?

Riffell: We hope this provides motivation to examine how learning by disease vectors influences biting, and hence disease transmission. We’re also hopeful that this study and others provides motivation to understand how the mosquito brain processes information to drive behavior, like seeking hosts. Dopamine is an important neuromodulator, and we're hopeful that this study could lead to tools for more effective mosquito control.

Featured image courtesy of Kiley Riffell.