Winter Weather Could Decide How Bad Mosquito Season Gets

PROVO, Utah — With varying temperatures and winter weather patterns across the country PCOs may be dealing with drastically different mosquito populations as spring and warmer weather approaches.

Trent Frazer, lead entomologist and senior director of quality assurance, Aptive Pest Control, said mosquitoes operate, develop and grow based on temperature. He said 50 degrees Fahrenheit is the known line for most mosquitoes to be able to live normally.

“When we have a mild winter, you kind of lose that reset that most winters bring to the mosquito population,” Frazer said. “Mosquitoes also gain the time in spring. So, when you have a mild winter, you have kind of a compounded problem when it comes to mosquitoes.”

During a typical cold winter, the adult mosquito population will usually freeze off and die depending on the species, with an overwintering stage laying eggs.

“Come spring melt and thaw, which creates water, the eggs hatch,” Frazer said. “Then you have that reset time where the eggs continue to develop and become adults. When we have a mild winter, you don’t kill of that adult population with those freezing temperatures. They can survive the winter and then come springtime, they’re ready to go.”

This warmer weather starts the mosquito lifecycle earlier with a more advanced population of sexually mature mosquitoes.

“A mild winter creates this compounded mosquito population problem that will affect the entire spring, summer and fall because those populations grow exponentially,” Frazer said. “So, that problem that started in a mild winter will last all summer long.”

Harsher winters lead to a smaller adult population though the temperature is still a factor with some species able to survive down to 14 degrees Fahrenheit. Frazer said a harsh winter would kill of the adults leading to a normal mosquito cycle that starts with the egg population that then becomes an adult.

Rapid change in temperature also plays a factor in the survivability of adult mosquitoes.

“Mosquitoes will survive the winter by building up fat reserves before the cold weather onset,” Frazer said. “They actually build those fat reserves, this is all species dependent, but they’ll switch from sucking blood to eating nectar and sugary fluids to build up these fat reserves.”

These fat reserves help mosquitoes survive in the winter.

“When you have a warm spell in the winter, those mosquitoes think it is springtime,” Frazer said. “They start moving, metabolizing and they start flying around, which burns more energy and those fat reserves. It also starts exposing them more than it would have had they spent the entire winter in diapause. If you have a cold spell after the warm spell, that can actually knock down the population.”

This is due in part to the adult mosquito population flying out of their hiding places, but also due to the population expending its reserve energy through the burning of its fat reserves. This further exposes the adult mosquito population to colder temperatures leading to their likely death.

Frazer said while adult mosquitoes feel the effects of winter weather, eggs are largely unaffected.

“Eggs are super hardy,” he said. “They are the evolutionary way that mosquitoes have figured out how to survive the wintertime. Some species lay eggs in mud where there will be spring overflow and runoff. “

Other species may lay their eggs in a raft that will float in puddles and standing water, Frazer said, while others survive in the larval stage underneath the ice. Each of these is a way that mosquitoes have evolved to survive the winter.

Rapidly changing weather can also lead to fewer adult mosquitoes who are ready to reproduce on day one.

“Instead of a full population of adult mosquitoes getting to it right on day one, we’ll have a two-week head start for humans and a two-week delay for mosquitoes to begin that reproductive cycle,” Frazer said. “Mosquitoes are fairly uncomplicated creatures; they’re just temperature driven, but they reproduce wildly fast.”

Getting rid of any stagnant water, whether it be buckets, tires, pool covers or tiny puddles is the best way to control the mosquito population, Frazer said.

“If you do that, and especially if you can get your neighbors to do that as well, you will have a head start or you will be able to reduce the population of mosquitoes since they actually don’t fly far,” he said. “They’re not migrators, so if you can create an environment that is free of standing water, then you have a reduced mosquito population.”

Frazer discussed how mosquitoes survive winter in a video posted here.