Mosquitoes in winter? Scientists say pests will be a year-long problem thanks to climate change

GAINESVILLE, Fla. — Mosquitoes are one of the few unpleasant parts of summer. As the temperature rises, these disease-carrying pests become a common sight, especially around standing water. Thankfully, these tiny nuisances don’t follow us into the winter, right? Wrong. According to researchers in Florida, climate change will likely keep mosquitoes active even in the colder months of the year.

A team from the University of Florida adds, in places seeing the greatest effects of climate change, mosquito activity could soon become a year-round problem.

“In tropical regions, mosquitoes are active all year, but that isn’t the case for the rest of the world. Outside of the tropics, winter temperatures cause mosquitoes to go into a kind of hibernation called diapause. We call these mosquitoes ‘cold bounded’ because their activity is limited by these lower temperatures,” says Brett Scheffers, assistant professor in the UF/IFAS wildlife ecology and conservation department, in a university release.

“However, with climate change, we expect summers to get longer and winters to become shorter and warmer. What will that mean for those cold bounded mosquitoes? How will they respond?”

Mosquitoes have a ‘plastic’ nature?

To see just how adaptive mosquitoes are already becoming to changing temperatures throughout the year, researchers collected these insects during each season in Gainesville, Florida.

“We found that the mosquitoes in our study are what we call ‘plastic,’ meaning that, like a rubber band, the range of temperatures they can tolerate stretches and contracts at different times of year,” Scheffers reports.

During the spring, when it’s cold at night but warms up during the day, mosquitoes appear to have a tolerance for a very large range of temperatures. By the summer, that range actually contracts as temperatures typically stay hot all the time. However, when the weather cools off in the fall, mosquitoes see their tolerance stretch out again.

“That tells us that as climate change makes our autumns and winters warmer, mosquitoes in more temperate regions are well prepared to be active during those times,” Scheffers explains.

“Our results suggest that to better understand how well populations and species may be able to tolerate ongoing climate change, we need to measure species thermal responses across different times of the year,” adds study first author Brunno Oliveira. “This information would help us to deliver a more accurate representation of the temperature range a species can tolerate.”

Mosquitoes love the heat and hunt animals who breathe

Study authors captured over 28,000 insects from 18 different mosquito species during their experiment. Scientists lured the pests in using a trap that emits carbon dioxide gas. Mosquitoes seek out this gas, which both humans and animals exhale when they breathe. For these pests, the gas signals that a tasty meal is nearby.

The team randomly selected 1,000 of these mosquitoes to test in their lab temperature experiment. They placed each insect in a test tube before putting it in water. From there, researchers continued to change the temperature, from cold to hot. At the same time, the team monitored when each mosquito became inactive — marking their upper or lower temperature thresholds.

“It was surprising to see how well these little creatures could tolerate high temperatures during the experiments, often well above the mean ambient temperatures measured by the weather stations,” says study co-author Gécica Yogo.

As for what is allowing mosquitoes to make these rapid adjustments to the weather, the answer is still unclear. However, researchers believe evolution could be working at a much faster rate in tinier creatures.

“Many people do not realize how quickly natural selection can act on short-lived animals,” explains Daniel Hahn, a professor in the UF/IFAS entomology and nematology department. “Whether the changes we are seeing in mosquito thermal properties are due to rapid natural selection across seasons, seasonal plasticity – much like a dog changing its coat — or a combination of both, is what we are working on now.”

The keys to keeping insects away year-round

Study authors believe their findings will help communities better prepare for insect season as climate change continues to lengthen summer. The team says one of the biggest things people can do to limit mosquito breeding is get rid of any standing water and cover items that could hold water, such as bottles, tin cans, garbage, outside water fixtures, and boats.

“The more mosquito activity there is, the greater the risk of these diseases spreading. Knowledge is power, and knowing that mosquitoes will be more active for more of the year can inform how we get ready for climate change,” Scheffers concludes.

The findings appear in the journal Ecology.

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