Alaska’s dry summer could mean more mosquitoes next year, entomologist says

An Anchorage mosquito that did not survive the process of natural selection. (Nat Herz/Alaska’s Public Media)

As a recent transplant to Talkeetna, KTNA reporter Nell Salzman found herself shocked and annoyed by the swarms of mosquitoes. So she called up entomologist Derek Sikes at the University of Alaska Fairbanks to learn more about them.

“Mosquitoes could be considered to be these very fancy machines for turning blood into more mosquitoes,” he said.

The purpose of mosquitoes is to make more mosquitoes. And they’re really good at it.

There are 30 mosquito species in Alaska. There are 20 in Interior Alaska, though in any one place you won’t see more than ten. Most are in the Aedes genus.

“They are faster flying, much more numerous, far quicker to bite,” Sikes said.

They winter as eggs in water. The eggs hatch in the spring, and then the larvae feed in the water, pupate and emerge as adults in May.

Then have two things in mind: they want to mate, then feed. All mosquitoes that drink blood are female. Males, alternatively, feed off nectar.

“But the females only get the blood to make eggs, in order to provide food for their offspring,” Sikes said.

Carbon dioxide stimulates the female to start host-seeking. They buzz around our heads because that’s where we expel the most CO2. All summer, they’re busy biting.

“Once we start getting below freezing temperatures at nighttime, which happens sometime in September usually, then the mosquitoes start disappearing,” Sikes said.

This explains why the ends of most Alaskan summers are mosquito-free.

Sikes says populations of mosquito species are shifting.

“This one that’s moving north, this is the species Culex tarsalis. It’s moving north probably because of warming temperatures. And so we do expect, globally, species to expand their ranges northward, and so we could start seeing disease transmission in areas that don’t have it right now,” he said.

Culex tarsalis transmits diseases like norovirus. Sikes would not be surprised if, by the end of this century, it became thoroughly established in places like Alaska.

But in the long term, warming trends could lead to a decrease in mosquito populations. Sikes says that permafrost in northern Alaska is shrinking. Permafrost keeps water from evaporating and helps maintain breeding grounds.

“There is going to be less standing water, and that will probably affect the mosquito populations,” he said. “I mean, if we fast-forward 200 years, 300 years in the future and there’s no permafrost in Alaska, I imagine there will be a lot fewer mosquitoes.”

Sikes says it’s hard to predict whether there will be a lot of mosquitos in a given summer, but there are four big factors in play: “Water, temperature, predators and competitors.”

A bad mosquito year happens when all those variables line up in the mosquitoes’ favor.

But Sikes says entomologists haven’t been able to find strong patterns between rainfall and mosquito abundance. There is the general rule that a wetter year leads to more mosquitoes, but there are exceptions.

“Mosquito abundance can be higher after a drought year,” he said.

A recent study found that drought will empty out a lot of temporary water bodies, killing other insects — the mosquitoes’ predators and competitors.

“The year following, when the rain fills up those water bodies, the mosquitoes are able to colonize them and breed in a mostly predator-free environment. So their populations can get huge,” he said.

Which means that this summer’s drought doesn’t bode well for next year’s mosquito season.

Sikes says this is why spraying for mosquitoes isn’t a good idea. It’s similar to the “drought-year” effect. It kills all their competitors and predators.

I asked Sikes about a mosquito-specific insecticide. What if we could get rid of just the mosquitoes?

“Mosquitoes transmit so many diseases among wildlife and drink so much blood that,” Sikes said. “It would probably be for the net benefit of humanity, even if there were some small ecological consequences.”

Sikes says it probably wouldn’t be a major problem if mosquitoes disappeared completely.

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