After a string of warm summers, the Kenai Peninsula’s spruce bark beetles are now hitting their highest numbers since their last outbreak in the 1990s.

“We’re seeing levels we haven’t seen for over a decade, since the late 90s,” said entomologist Matt Bowser of the Kenai National Wildlife Refuge.

The U.S Forest Service and the Alaska Division of Forestry have run annual aerial surveys since the 1970s. This year’s survey found 405,000 acres of beetle damage — the most in a given year since 1997, according to Forest Health Program Manager Jason Moan of the Alaska Division of Forestry. About 95 percent of the statewide damage was in southcentral Alaska, Moan wrote in an email, with the majority in the Susitna Valley.

Spruce bark beetles outbreaks are cyclical, depending on the prevalence of mature trees and the warm, dry conditions that make them vulnerable to beetle attack. Prior to the 1990s outbreak, the last major spike in spruce beetle population was in the 1880s, according to tree ring studies by former Fish and Wildlife Service ecologist Dr. Ed Berg, who predicted a coming spruce beetle outbreak in a 2015 article.

“It’s not a surprise at all — it’s just a matter of when,” Bowser said of the present outbreak. “This is a beetle that’s been here a long time… It’s not a new thing. This is one of the forest happenings we understand better than a lot of others — we know that all it takes is susceptible trees — a mature enough forest — and then runs of warm summers. If you have those things put together, you have at least the potential for an outbreak.”

With the peninsula seeing above average temperatures in the past two summers and a population of mature spruce on the north peninsula — which was less impacted by the 1990s outbreak than the south peninsula — the conditions are once again favoring the beetles, which bore through spruce bark to eat and lay eggs in the tree’s circulatory tissue, or phloem.

When beetle populations rise, they can do so rapidly. On the Kenai Peninsula, aerial surveys saw 7,000 acres of damage in 2015 and 16,000 damaged acres in 2016. 2017’s survey found 55,000 acres of damage, “primarily in the northwestern portion of the peninsula west of the Kenai Mountains and north of the Kenai River,” Moan wrote.

The Kenai National Wildlife Refuge’s response to the natural event is “mostly hands-off,” Bowser said, aside from cutting down beetle-killed trees near roads and campgrounds. Some private property-owners who stand to lose favorite trees are less sanguine about the cycles of the beetle population. At a Nov.7 workshop for property owners put on by the Alaska Division of Forestry and the University of Alaska Fairbank’s Cooperative Extension service, Soldotna attorney Joe Kashi was among the attendees seeking information on how to fight the beetle.

Kashi said that after seeing some of the north peninsula beetle kill on a casual flight over the area, he became concerned about his property north of Sterling, which he said has some big, old trees, including a “a 65 feet high, 19 inch diameter, full-to-the bottom spruce” that he described as a prized tree.

Sure enough, he found that several of his trees had bark coming off, a result of being attacked by woodpeckers seeking the beetles inside.

Kashi said that in spring, when the beetles emerge from the bark and begin to fly around in search of new food, he plans to use injected insecticides in surrounding trees and fertilize them to strengthen their resistance against infestation. Though insecticides are an ineffective way to kill beetles after they’ve infested a tree, they can be used preventatively on trees that haven’t yet been infected.

“I’m going to try to hit it multiple ways,” Kashi said. “…I’ll do what I can, and if I can’t save it, I’ll feel bad but I won’t feel that I screwed up.”

For more information on controlling beetle infestations, you can contact the Soldotna office of the University of Alaska’s Cooperative Extension Service at 907-262-5824.

Reach Ben Boettger at ben.boettger@peninsulaclarion.com