This year’s new generation of eager young spruce bark beetles may soon be emerging from the bark of local trees where they’ve spent the winter maturing and feeding. Homeowners looking to protect a prized spruce can spray the trunks of their trees with preventative insecticides, but they should do so soon.
“There are some pesticides that work, but they have to be sprayed before the beetles get there,” said U.S Forest Service Supervisory Entomologist John Lundquist. “And the beetles are going to start flying here in the next week or two … They’re getting ready. We’ve dug into some trees, and they’ve got wings, and they’re adults, and they’re ready to move.”
After boring into the bark of a spruce tree, the beetles eat the tree’s circulatory tissue, or phloem. When this tissue is cut off all the way around the trunk, the tree starts to die.
Female beetles lay up to 150 eggs in galleries excavated beneath the bark, and after spring temperatures rise, they emerge to seek new trees between mid-May and July. Kenai National Wildlife Refuge entomologist Matt Bowser said the peak of beetle-flight has usually been in the first weeks of June.
Spruce bark beetles are native to the region and always present in its trees, though a series of warm, dry summers can cause their population to explode, killing thousands of acres of spruce. Such an outbreak began around 2015 and is ongoing, Lundquist said.
The U.S Forest Service and the Alaska Division of Forestry have counted beetle-killed trees in annual aerial surveys since the 1970s, and in 2017 found more acres of beetle damage than any year since 1997 — the midst of the last beetle outbreak in the late 1990s. Most of the damage is in the Susitna Valley, though the Kenai Peninsula had 55,000 acres of damage, mostly in the north and west. Lundquist said there are many beetle-killed trees in the Swanson River area.
The fresher beetle-killed trees aren’t visible yet in aerial surveys, Bowser said.
“You can see right around here, especially in the woods around Soldotna, there are a lot of trees that are still green on the top — so if you were looking at them in an aerial survey they would not look dead — but they’ve been hit hard in the last couple years,” Bowswer said. “And I expect to a big pulse of beetles this year — there will be more beetles, and more dying trees, and the damage will be more conspicuous soon. Even if the outbreak stops this season, there are damaged trees from previous seasons that are green on top and going to have red needles soon.”
The aerial surveys of damaged trees each July mostly show the effects of the last year’s beetle activity.
“A lot of what was killed last year is going to show up this year — it takes a year before the trees actually turn brown,” Lundquist said. “So it’s going to give the perception of a much more intense, widespread outbreak this year.”
To measure the beetle population before damage becomes visible from the air, Lundquist said the Forest Service and the U.S Bureau of Land Management will also be studying beetle abundance with a network of pheromone traps across the state, which can show the population increase before it become visible in the trees.
“We should have a good idea now how far north it is, and how far east,” Lundquist said.
This spring, so far cool and damp, may favor the surviving spruce over the beetles, depending on how long the cool streak continues.
“It would help with the trees that are still fighting, the trees that are still healthy, if we continue to have cool wet weather into the summer,” Bowser said. “It would slow the outbreak, or have the potential to — but there’s some inertia. We have a lot of beetles hatching out this spring.”
Reach Ben Boettger at firstname.lastname@example.org.