Summer preview: Mosquito eggs undaunted by freezing temps

A prolonged freeze should mean fewer mosquitoes this summer, right?

Wrong, said Amanda Beehler, manager of the Benton County Mosquito Control District.

“We have dormant mosquito eggs out there waiting to hatch and become spring mosquitoes,” she explained.

Tropical mosquito varieties, such as the ones carrying the dreaded Zika virus, perish in cold temperatures. Unfortunately, the strains inhabiting the Mid-Columbia are made of sterner stuff.

“The kind of mosquitoes we have are fine with low temperatures. They’re going to tough it out,” she said.

It is too early to predict what 2017 will bring in terms of mosquitoes. More than a painful nuisance, local mosquitoes spread the potentially deadly West Nile Virus and other diseases.

Beehler said mosquito populations depend on the amount of eggs laid the previous year and on weather patterns through the spring.

Benton County Mosquito Control recorded low numbers in its 2016 mosquito traps, unexpectedly comparable to 2015, a drought year.

Even if there are fewer eggs to hatch, it doesn’t take many mosquitoes to create a problem. The bugs are basically designed to reproduce en masse.

“One mosquito can lay a lot of eggs, 200 to 400 at a time.”

Spring weather plays a bigger role in determining if mosquito eggs hatch and become breeding adults.

Mosquito eggs hatch when the temperatures rise. But a warm up followed by another freeze could kill the larvae before they can mature and mate. Or the weather could simply warm up enough to produce hatching and stay that way.

“The weather is warm enough that they don’t die, so they go out and bite and breed,” Beehler said.

The volume of moisture falling in winter is another factor. Thawing snow carries off dormant mosquito eggs as it washes through canals and rivers.

Mosquito control districts run year-round. They work to actively control as soon as the weather turns, typically in April but often in March and continue through hunting season to October.

Staff spend the winter reviewing operations, repairing and updating equipment, evaluating what did and didn’t work in the prior season, and working to comply with the wide variety of local, state and federal regulations that govern their operations.

When temperatures begin climbing, it will begin the season-long eradication effort and monitoring for mosquito eggs and larvae. The mosquito strains that carry the deadly Zika virus aren’t found this far north, but local varieties carry the West Nile Virus.

The Washington State Department of Health reported nine cases of humans contracting West Nile virus in 2016, including three cases where the infection occurred in Benton County. One of the local victims passed away. No cases were attributed to Franklin County.

West Nile was detected in 25 mosquito samples collected in Benton County, six in Franklin County and 51 in Grant County.

This story was originally published January 14, 2017 at 1:47 PM with the headline "Summer preview: Mosquito eggs undaunted by freezing temps."