What Winter does to Mosquitoes

Winter weather conditions can play a major role in shaping mosquito populations, creating different challenges for pest management professionals during spring and summer.

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

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

MILD WINTERS, BIGGER PROBLEMS. During a typical cold winter, adult mosquitoes often freeze and die, depending on the species, while eggs overwinter.

“Come the spring melt and thaw, which creates water, the eggs hatch,” Frazer said. “Then you have that reset time where eggs develop and become adults. When we have a mild winter, you don’t kill off that adult population. They survive and are ready to go in spring.”

Warmer winters start the mosquito life cycle earlier, with a more advanced population of sexually mature insects.

A mild winter creates a compounded mosquito population problem that affects spring, summer and fall because populations grow exponentially,” Frazer said. “That problem lasts all season.”

Harsher winters typically reduce adult populations, though some species can survive temperatures as low as 14 degrees. In those cases, the cycle resets with eggs developing into adults.

TEMPERATURE SWING IMPACT. Rapid temperature changes also affect mosquito survival.

“Mosquitoes survive winter by building fat reserves before cold weather,” Frazer said. “They switch from blood feeding to nectar and sugary fluids to build those reserves.”

Those reserves sustain them through winter, but warm spells can disrupt that process. “When you have a warm spell, mosquitoes think it’s spring,” Frazer said. “They start moving and burning energy. If a cold spell follows, that can knock down the population.”

This happens partly because mosquitoes leave protected areas and expend energy, making them more vulnerable to cold temperatures.

WHY EGGS PERSIST. While adult mosquitoes are affected by winter weather, eggs are largely unaffected.

“Eggs are super hardy,” Frazer said. “They are how mosquitoes survive the winter.”

Some species lay eggs in mud that will flood in spring, while others lay floating egg rafts in standing water. Still others survive as larvae beneath ice — all evolutionary strategies to endure winter.

Rapid weather changes can also delay early-season mosquito activity. “Instead of a full population reproducing on day one, we may see a two-week delay,” Frazer said. “Mosquitoes are temperature-driven, but they reproduce very quickly.”

PREVENTION STARTS AT HOME. Eliminating standing water in buckets, tires, pool covers or puddles is the most effective way to control mosquito populations, Frazer said.

“If you can do that, and get neighbors to do it as well, you’ll have a head start,” he said. “Mosquitoes don’t travel far. If you remove standing water, you reduce the population.”

The author is digital editor of PCT.