Unlocking the mystery of host preference and learning in mosquitoes

Insects exhibit sophisticated and complex behaviors, but they have miniature nervous systems with low numbers of neurons. Nonetheless, insects can exhibit the same complex behaviors as rats or dogs: for instance, insects can learn various cues as predictors of reward, or punishment, and some insects can learn concepts, and even numerosity. These results raise a fundamental question: how do insects generate such complexity with so few neurons? As part of our HFSP project, we have been working towards quantifying higher-order cognitive behaviors in insects and unraveling the neural circuits responsible for cognition.

HFSP Program Grant holder Jeffrey Riffell and colleagues
authored on Thu, 12 April 2018

One of the insects we have worked on is the tiger mosquito, Aedes aegypti. These mosquitoes are intense vectors of disease such as West Nile, Chikungunya, and Zika viruses. Mosquitoes can target specific individuals, and they can easily change their host preferences. How are mosquitoes selecting certain individuals over others, and shifting their preferences? The mosquito’s ability to learn to recognize its targets could be one explanation.

Figure 1: Aedes aegypti mosquitoes (pictured) prefer to bite certain individuals over others. Photo credit: Kiley Riffell

As a first step, we trained mosquitoes the association between an odor and a vibration. For the vibration, we gently vibrated the mosquitoes at similar forces to what they might experience if you shook your arm. Mosquitoes quickly learned the association between the host odor and vibration. Once learned, the aversive responses were similar to how mosquitoes react to DEET, currently one of the most effective mosquito repellents!

Figure 2: A tethered Aedes aegypti mosquito. Photo credit: Kiley Riffell

One critical chemical for learning and motivation in diverse animals, ranging from humans to honeybees, is dopamine. Using genetically modified mosquitoes with defective dopamine receptors, we found that mosquitoes could no longer learn. We next recorded from 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 suppresses its ability to learn, while also decreasing its ability to process odor information. These experiments also demonstrate the amazing flexibility insects have in their learning abilities, and by using such small miniature brains.

Reference

Modulation of Host Learning in Aedes aegypti Mosquitoes. Vinauger C, Lahondère C, Wolff GH, Locke LT, Liaw JE, Parrish JZ, Akbari OS, Dickinson MH, Riffell JA. Curr Biol. 2018 Feb 5;28(3):333-344.e8. https://doi.org/10.1016/j.cub.2017.12.015.

Pubmed link