"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", says senior author Jeff Riffell, a professor of biology at the University of Washington.
Interestingly, although the insects learned to avoid the smell of humans and rats, they could not make the same association with the odor of a chicken. A recent study published by a team from the University of Washington suggests that mosquitoes have the ability to associate scents with mechanical shocks, and are thus capable of learning what types of odors to avoid. The researchers found that's also true in mosquitoes, helping them learn and process odor-related information. They repeated this test with mechanical vibrations thrown into the mix, and the effect on the mosquitoes was dramatic.
They can actually learn to associate movements like swatting or shivering with human odors, according to a.
"Moreover, mosquitoes remember the trained odors for days", he added.
A chemical message in mosquitoes' brains meant the insects were warned when they thought they might be about to be squashed.
Researchers determined this by exposing mosquitoes to a choice between a sleeve that either had a human odor or did not. Some mosquitos were genetically modified not to have dopamine receptors and were trapped in an arena of sorts while scientists studied the insects' brain activity.
Along with the discovery that mosquitoes can learn to avoid particular odours, Riffell and his team have also investigated mosquitoes' ability to learn favoured hosts.
Twenty-four hours later, the same mosquitoes were assessed in a Y-maze olfactometer in which they had to fly upwind and choose between the once-preferred human body odor and a control odor.
Researchers already knew that mosquitoes don't decide whom to bite at random. The researchers then 3D printed a miniature arena into which they glued the mosquitoes, allowing them to fly in place while the researchers recorded the activity of neurons in the olfactory centers of their brains. They 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. Here, we show that olfactory learning may contribute to Aedes aegypti mosquito biting preferences and host shifts. We further show through combined electrophysiological and behavioral recordings from tethered flying mosquitoes that these odors evoke changes in both behavior and antennal lobe (AL) neuronal responses and that dopamine strongly modulates odor-evoked responses in AL neurons.
In addition to encouraging people to swat mosquitoes as much as possible, the research may prove valuable in large-scale mosquito control and prevention of transmission of mosquito-borne diseases. "Training and testing to scents of humans and other host species showed that mosquitoes can aversively learn the scent of specific humans and single odorants and learn to avoid the scent of rats (but not chickens)", the researchers wrote in their study.
Authors of the paper include Clément Vinauger, Chloé Lahondère, Gabriella H. Wolff, Lauren T. Locke, Jessica E. Liaw, Jay Z. Parrish, Omar S. Akbari, Michael H. Dickinson, and Jeffrey A. Riffell.