Mosquitoes learn from damage

You’d think they’re driven by mere bloodlust – but mosquitoes are also capable of “clever” behavior, as the study shows: If you’ve just avoided death with an insecticide, insects avoid experimenting with its scent. Learning to learn could therefore play a role in the resistance of dangerous disease vectors to control measures, the researchers said.

As you know, these are not only hated pests – mosquitoes are considered the most dangerous animals in the world: some species spread diseases such as malaria, dengue and yellow fever, from which at least half a million people die each year. Various strategies are currently under development to tackle the problem. However, the chemical club still remains an important weapon in the fight against mosquitoes: different active ingredients are used in different ways. An important strategy is to treat mosquito nets or surfaces with active ingredients on which bloodsuckers settle. Through contact, they absorb toxins and die – this is a concept.

Because of simple bloodsuckers

However, the use of these methods has already led to the development of immunity in mosquitoes: they form stronger protective layers or produce active substances that break down toxins. So far, however, less attention has been paid to another possible aspect that may limit the effectiveness of treatments: it seems possible that mosquitoes might learn to avoid insecticides on an individual level. Because it is already common knowledge that mosquitoes can use certain experiences for themselves. For example, they can learn to associate previously unknown smells with the chance of a blood meal. In their research, scientists led by Seynabou Sougoufara of Keele University (UK) have now investigated the opposite effect: are mosquitoes learning to associate certain odors with sub-lethal poisoning?

They conducted experiments with two known species of mosquitoes: the Aedes aegypti yellow fever mosquito and the domestic mosquito Culex quinquefasciatus. They placed some animals in paper jars containing non-lethal doses of malathion, propoxur, deltamethrin, permethrin, and lambda-cyhalothrin. While the animals apparently survived it unscathed, it can be assumed that they felt the poison – they probably felt unwell. The mosquitoes that had to remain in the same vessels served as controls – but no poison. Instead, the paper was soaked with harmless oil. The researchers then conducted experiments to investigate the extent to which treated mosquitoes exhibited abnormal behavior when exposed to pesticides in various ways.

Survival through clever behavioral adaptation

Studies have shown that mosquitoes that had previously been exposed to one of the insecticides extremely often refused to pass through a hole in the net treated with these agents in order to reach an enticing source of blood: most untreated test animals squeezed. through the opening, while only about 15 percent of “experienced” mosquitoes dared to do so. Subsequent studies showed how reasonable this “wise” decision was: during the passage, mosquitoes came into contact with the poisoned web and often died from it. Most importantly, treated mosquitoes benefited from their avoidance thanks to their high survival rate.

The researchers also found that pre-exposed mosquitoes generally avoided the smell of pesticides. In these experiments, the animals were given a choice of two rest containers, one smelling of pesticide and the other smelling of control substance. Assessments showed that 76 percent of A. aegypti and 83 percent of C. quinquefasciatus that had previously been exposed to pesticides rested in a pesticide-free container. On the other hand, inexperienced controls did not show this preference and were also looking for a container that smelled of insecticide.

Importance for the control strategy

According to the researchers, this shows that the behavioral adaptation experienced by mosquitoes is important: they are more likely to look for food sources and places to rest, which increases their chances of survival and reproduction. As the scientists explain, it can also be assumed that non-lethal experiments of pesticides occur very often in practice. Because if surfaces are not constantly wetted, concentrations can easily drop below lethal levels. In this case, the toxins can make the mosquitoes smart in a way that is problematic for us.

‘The results highlight the role of mosquito cognition in pesticide resistance in chemically controlled mosquito populations,’ the researchers write. Therefore, they are now calling for more detailed research into the fundamentals of behavioral flexibility in these insects. “Ultimately, better understanding can lead to more effective control strategies that bypass the behavioral aspect of mosquito resistance,” say Sougoufara and his colleagues.

Source: Scientific reports, doi: 10.1038 / s41598-022-05754-2

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