Mosquitoes Have Learned to Avoid Pesticides Used to Kill Them Says a UK Study

Mosquitoes are getting smarter these days. With the changing environment, they are adapting to new ways of survival. According to the scientists at Keele University in the U.K, they are learning new ways to avoid pesticides used to kill them.

Scientists studied two species of mosquitoes Culex quinquefasciatus and Aedes aegypti. These two species are responsible for spreading diseases such as West Nile Fever, Zika, malaria, yellow and dengue fever. In recent years, pesticide resistance among mosquitoes has increased. However, the extent of this ability in different species of mosquitoes is still unknown. Scientists found that the female mosquitoes have learned to identify the smell of venomous pesticides after a single harmless exposure to pesticides.

During the experiment, researchers exposed female mosquitoes to safe doses of common anti-mosquito pesticides. They observed that mosquitoes that were earlier exposed to these pesticides avoided passing through the net treated with the same pesticide to reach the food source kept behind it. 

Also, the rate of recognizing the pesticide’s smell was higher in pre-exposed mosquitoes than those of non-exposed ones. Consequentially, the survival rate was more than two times higher in these mosquitoes. The experiment results suggested that mosquitoes who learned to avoid venomous pesticides may find safe food resources and resting sites to live and reproduce.

The researchers conducted a similar experiment but with controlled substances such as malathion and naled. They discovered that pre-exposed mosquitoes rested on containers that smelled of controlled substances and avoided pesticide smelled containers.

“Mosquitoes have been learning. We just didn’t know about it,” said Frederic Tripet, a behavioral ecologist and director at the Centre for Applied Entomology and Parasitology at Keele University.

In 2012, Tripet performed another research that highlighted the visual and olfactory (smell) associated learnings of Anopheles gambiae, a malaria vector (disease carrier). The study suggested that mosquitoes were capable of learning. They could associate different patterns, visual signs and smells in the surroundings with negative or positive experiences. These findings from the previous experiment were critical in understanding the results of the recent experiment. It could be that mosquitoes exposed to pesticides for the first time had a negative experience. Therefore, they avoid its smell when exposed to it the second time.

“So they’re there. They get this first bad experience,” said Tripet. “And if we don’t kill them at first instance, then they learn to avoid that.”

Learning abilities of mosquitoes are helping them develop physiological resistance against anti-mosquito pesticides. Therefore, the combination of their learning skills and pesticides resistance abilities are allowing them to survive even in the presence of pesticides in the surroundings making them less effective in controlling the mosquitoes population.

Hence, new methods or solutions are required for the same. One way can be to formulate a chemical compound that has a delayed effect on mosquitoes. So, if the insect has encountered the chemical the first time and didn’t die, it will not associate the chemical’s smell with a negative experience and won’t avoid it the second time.

Another way to disrupt their learning can be to add an attractive smell to pesticides so they can relate this smell with a positive experience or pleasure and won’t ignore it, researchers suggest. 

The research has been published in the Journal Scientific Reports.

Contributed by: Simran Dolwani