Mosquitoes could become active year-round

A new study from the University of Florida has shown that mosquitoes could become active year-round in places where they are usually dormant in the winter. The experts found that mosquitoes can adjust to rapid temperature changes.

“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,” explained study senior author Professor Brett Scheffers.

“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?” 

To investigate, the researchers conducted experiments with mosquitoes collected at more than 70 sites in and around Gainesville, Florida, which is located on the dividing line between subtropical and temperate climates. 

Overall, about 1,000 mosquitoes were randomly sampled for lab testing. The experts analyzed how mosquitoes responded to changes in temperature while considering what time of year they were collected. 

“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,” said Professor Scheffers.

The study revealed that the mosquitoes’ tolerable temperature range stretched out in the spring to include both warmer days and colder nights. In the summer, when the nights are warmer, their suitable temperature range contracts. 

In autumn, when temperatures begin to cool off, the range stretches again, explained Professor Scheffers.

“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,” said Professor Scheffers.

“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,” said study first author Brunno Oliveira.

“This information would help us to deliver a more accurate representation of the temperature range a species can tolerate.”

To establish the upper or lower temperature thresholds, the researchers monitored the activity of each mosquito, which was placed in a vial that was then put in a water bath. Over time, the researchers changed the water temperature. When the mosquitoes became inactive, it was a signal that the upper or lower threshold had been reached. 

“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,” said study co-author Gécica Yogo.

According to the researchers, it is not yet clear what allows mosquitoes to adjust to rapid changes in temperature.

“Many people do not realize how quickly natural selection can act on short-lived animals,” said study co-author Professor Daniel Hahn. 

“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 experts noted that insights from this study can help communities better prepare for the impacts of climate change as they relate to mosquitoes, which spread diseases that affect humans and animals.

“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,” said Professor Scheffers.

“When we talk about how climate change might affect plants and animals, we are often talking about species moving to new areas because the conditions are changing — in other words, the arrival of something new. However, climate change will also affect species we live with right now, like highly flexible mosquitoes, and that’s another aspect to consider.”

The study is published in the journal Ecology.

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By Chrissy Sexton, Earth.com Staff Writer