Most of us think of mosquitoes as irritating little pests, plaguing us during the summer months when open windows are a necessity. But new research, reported in Current Biology on January 25 shows that mosquitoes can learn to associate a particular odour with an unpleasant mechanical shock akin to being swatted. As a result, they’ll avoid that scent the next time.
“Once mosquitoes learned odours in an aversive manner, those odours caused aversive responses on the same order as responses to DEET, which is one of the most effective mosquito repellents,” says Jeffrey Riffell at the University of Washington, Seattle. “Moreover, mosquitoes remember the trained odours for days.”
If you’ve ever been on a family holiday, or camping with your friends under the stars, you may have realised that mosquitoes don’t decide whom to bite at random. They show obvious preferences for some people over others. Mosquitoes are also known to alternate hosts seasonally, feeding on birds in the summer and mammals and birds during other parts of the year, for instance. Riffell and his colleagues wanted to find out more about how learning might influence mosquitoes’ biting preferences.
Firstly, the researchers trained mosquitoes by pairing the odour of a particular person or animal species (a rat versus a chicken) with a mechanical shock. For the mechanical shock, a vortexer machine was used simulate the vibrations and accelerations a mosquito might experience when a person tried to swat them. The mosquitoes swiftly learned the association between the host odour and the mechanical shock and used that information in deciding which direction to fly. As a side note, they couldn’t learn to avoid the smell of a chicken.)
Learning in many animals, from honeybees to humans, depends on dopamine in the brain. Additional study showed that dopamine is also essential in mosquito learning. Genetically modified mosquitoes lacking dopamine receptors lost the ability to learn.
The researchers also glued mosquitoes to a custom 3D-printed holder that allowed the insects to still fly in place while the activity of neurons in the olfactory center of their brains was recorded. Those experiments showed that without dopamine, those neurons were less likely to fire. As a result, mosquitoes became less able to process and learn from odor information.
The findings may have important implications for mosquito control and the transmission of mosquito-borne diseases, such as Zika, dengue, chikungunya, and yellow fever:
“By understanding how mosquitoes are making decisions on whom to bite, and how learning influences those behaviours, we can better understand the genes and neuronal bases of the behaviours,” Riffell says. “This could lead to more effective tools for mosquito control.”
Now that we know that mosquitos learn to avoid certain hosts, it’s time to explore how mosquitoes learn and remember favoured hosts.
“In both cases, we think dopamine is a critical component,” Riffell says.
You can read the article here.