Mosquitoes learn to avoid pesticides after just one non-lethal dose

Experiments show that two species of mosquitoes change their behaviour after exposure to five common pesticides, which could make the chemicals less effective

By Chen Ly

Mosquitoes can learn to avoid pesticides after just one exposure to them, which means current pesticides may not be as effective as we thought as against the insects.

Millions of people a year contract diseases that are transmitted by mosquitoes, such as malaria, Zika, dengue and West Nile fever. Pesticides are a common tool for controlling mosquito populations, but insects become more resistant to them over time.

This resistance arises due to a range of factors, including biological changes in mosquitoes. Frédéric Tripet at Keele University in the UK and his colleagues decided to test whether mosquitoes could also learn to avoid pesticides.

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In a laboratory, the researchers exposed two species of mosquitoes – Aedes aegypti and Culex quinquefasciatus – to non-lethal doses of five commonly used pesticides. Around 200 mosquitoes were introduced to each pesticide, all of which were female.

After exposure, the mosquitoes underwent two tests. In the first, the insects were placed in a box with food at the other end. The mosquitoes and the food were separated by a net laced with the same pesticide they were previously exposed to.

Just 15.4 per cent of A. aegypti and 12.1 per cent of C. quinquefasciatus mosquitoes that had been pre-exposed passed through the net, compared with 57.7 per cent and 54.4 per cent respectively that hadn’t been exposed before.

In the second test, the researchers offered the mosquitoes the choice to rest in either a container that smelled like the pesticide they were exposed to or a control substance. They found that pre-exposed mosquitoes were much more likely to rest in the pesticide-free container than those that weren’t exposed.

These findings show that mosquitoes are capable of learning behavioural resistance to pesticides. “What is quite interesting is that mosquitoes feel ill effects from the pesticides,” says Tripet. “They are capable of understanding that they’re uncomfortable, and they should avoid that experience.”

Tripet hopes these findings will help to inform new strategies for managing mosquitoes. For example, he suggests mosquitoes may be slower to learn avoidance behaviour if pesticides are combined with other smells that they find attractive.

Journal reference: Scientific Reports, DOI: 10.1038/s41598-022-05754-2