‘Pavlov’s mosquitoes’: Swatting has similar effect as insect repellent

In this photo, a mosquito’s response to various odors is tested.
Based on smell, mosquitoes may learn to avoid people who swat at them. In this photo, a mosquito’s response to various odors is tested.
Source: Image courtesy of Kiley Riffell.

When it comes to keeping mosquitoes away, swatting may have the same effect as the best insect repellents.

One swat may be enough, researchers said, and the findings may have implications for mosquito control efforts.

In laboratory experiments, researchers found that mosquitoes quickly learned to associate the scent of individual humans with an unpleasant mechanical shock that simulated a vibration on their skin that occurs when humans attempt to swat a mosquito but miss.

Once they learned this association, according to Jeffrey A. Riffell, PhD, associate professor of biology at the University of Washington, the mosquitoes showed an aversion to human scent akin to how they react to DEET, an effective insect repellent. Armed with this knowledge, mosquitoes will seek out another target.

“Essentially, Pavlov's mosquitoes,” Riffell told Infectious Disease News.

Scientists have known that insects as diverse as bees and moths can learn. But Riffell said little is known about how learning influences the biting preferences of insects like mosquitoes that feed on blood. Other biting insects have shown a preference for hosts that do not defend themselves.

Cattle and goats flick their tails to swat biting insects. But if the goats are sedated and unable to move, they receive 15 times more insect bites than nearby, unsedated goats,” Riffell said. “For the mosquito, the swat of a goat tail or human hand could lead to its death, and it would thus be advantageous for the mosquito to learn from these past experiences.”

Diseases spread by mosquitoes kill millions of people every year. According to Riffell, most of the spread is caused by relatively few people — just 20% of humans make up 80% of transmission. In their experiment, Riffell and colleagues trained Aedes aegypti mosquitoes — the main vector of Zika and other diseases — by pairing human odors with a mechanical shock caused by a machine called a vortexer. Later, these trained mosquitoes showed a lack of attraction to human odor in a Y-shaped maze where they had to fly upwind and choose between a human scent or a control scent.

“As it turns out, pairing a blend of human smells with vortexing has a profound effect on the mosquitoes’ host-seeking behavior: they lose their innate attraction to human hosts, acting just as though no odor was present at all,” Marcus Stensmyr, PhD, senior lecturer in the department of biology at Lund University in Sweden, and Current Biology editor Florian Maderspacher wrote in a related review of the research. “Given that naive mosquitoes show such a strong preference for human odors, the fact that they can overcome their natural urge after a single swatting experience is striking.”

Riffell and colleagues found that dopamine is involved in mosquitoes’ ability to learn a negative association between an odor and a vibration. Using CRISPR-Cas9 gene editing technology, they showed that knocking out the dopamine receptor Dop1 could impair their memory and make them less adaptable and more susceptible to control.

“But dopamine is also involved in general motivation in insects, so modifying the Dop-1 gene would be an attractive target [for a gene drive],” Riffell said. “It would impair the ability to learn, but also suppress general motivation.” – by Gerard Gallagher

References:

Stensmyr M, Maderspacher F. Curr Biol. 2018;doi:10.1016/j.cub.2017.12.056.

Vinauger C, et al. Curr Biol. 2018;doi:10.1016/j.cub.2017.12.015.

Disclosures: The authors report no relevant financial disclosures.

In this photo, a mosquito’s response to various odors is tested.
Based on smell, mosquitoes may learn to avoid people who swat at them. In this photo, a mosquito’s response to various odors is tested.
Source: Image courtesy of Kiley Riffell.

When it comes to keeping mosquitoes away, swatting may have the same effect as the best insect repellents.

One swat may be enough, researchers said, and the findings may have implications for mosquito control efforts.

In laboratory experiments, researchers found that mosquitoes quickly learned to associate the scent of individual humans with an unpleasant mechanical shock that simulated a vibration on their skin that occurs when humans attempt to swat a mosquito but miss.

Once they learned this association, according to Jeffrey A. Riffell, PhD, associate professor of biology at the University of Washington, the mosquitoes showed an aversion to human scent akin to how they react to DEET, an effective insect repellent. Armed with this knowledge, mosquitoes will seek out another target.

“Essentially, Pavlov's mosquitoes,” Riffell told Infectious Disease News.

Scientists have known that insects as diverse as bees and moths can learn. But Riffell said little is known about how learning influences the biting preferences of insects like mosquitoes that feed on blood. Other biting insects have shown a preference for hosts that do not defend themselves.

Cattle and goats flick their tails to swat biting insects. But if the goats are sedated and unable to move, they receive 15 times more insect bites than nearby, unsedated goats,” Riffell said. “For the mosquito, the swat of a goat tail or human hand could lead to its death, and it would thus be advantageous for the mosquito to learn from these past experiences.”

Diseases spread by mosquitoes kill millions of people every year. According to Riffell, most of the spread is caused by relatively few people — just 20% of humans make up 80% of transmission. In their experiment, Riffell and colleagues trained Aedes aegypti mosquitoes — the main vector of Zika and other diseases — by pairing human odors with a mechanical shock caused by a machine called a vortexer. Later, these trained mosquitoes showed a lack of attraction to human odor in a Y-shaped maze where they had to fly upwind and choose between a human scent or a control scent.

“As it turns out, pairing a blend of human smells with vortexing has a profound effect on the mosquitoes’ host-seeking behavior: they lose their innate attraction to human hosts, acting just as though no odor was present at all,” Marcus Stensmyr, PhD, senior lecturer in the department of biology at Lund University in Sweden, and Current Biology editor Florian Maderspacher wrote in a related review of the research. “Given that naive mosquitoes show such a strong preference for human odors, the fact that they can overcome their natural urge after a single swatting experience is striking.”

Riffell and colleagues found that dopamine is involved in mosquitoes’ ability to learn a negative association between an odor and a vibration. Using CRISPR-Cas9 gene editing technology, they showed that knocking out the dopamine receptor Dop1 could impair their memory and make them less adaptable and more susceptible to control.

“But dopamine is also involved in general motivation in insects, so modifying the Dop-1 gene would be an attractive target [for a gene drive],” Riffell said. “It would impair the ability to learn, but also suppress general motivation.” – by Gerard Gallagher

References:

Stensmyr M, Maderspacher F. Curr Biol. 2018;doi:10.1016/j.cub.2017.12.056.

Vinauger C, et al. Curr Biol. 2018;doi:10.1016/j.cub.2017.12.015.

Disclosures: The authors report no relevant financial disclosures.

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