Spruce beetles take flight in search of new host trees

Spruce beetle outbreak in the Mat-Su Valley seen during the 2017 aerial detection survey. (U.S. Forest Service photo)

Spruce beetles may be native to Alaska, but they can still devastate a spruce forest. Over the last two years, an outbreak concentrated in Southcentral Alaska’s Susitna River drainage and northwest Kenai Peninsula has affected more than 500,000 acres of forest. It’s the worst infestation since the 1990s.

Jason Moan of Alaska’s Division of Forestry says a combination of factors causes a population to grow to the level of an outbreak.

“Spruce beetle favors large-diameter, slow-growing trees,” Moan said. “If we have wind events or things like that where a large number of trees might be blown over, you know, beetles tend to favor that material. They’re able to build up populations.”

Moan said warm summers can also play a role because beetles tend to reproduce faster in warmer weather. It takes one to two years for the beetles to complete their life cycles, and then when the weather warms above 60 degrees, female beetles begin to take flight in search of new host trees, sending out pheromones to attract others when they’ve found a tree. Larger, unhealthy trees are more susceptible to infestations.

“Folks can start keeping an eye on the spruce that they do that are not attacked. Keeping those watered if they need it. Avoiding damage to those trees,” Moan said.

Signs of an infestation include clumps of sap and sawdust where the beetles have bored holes in the bark as well as pieces of bark scattered at the base of the tree. Discolored needles can also be an indicator but not always. Moan said once a tree is infested, there’s not much that can be done other than to remove it. Pesticides can be effective in preventing beetles before they take flight but not after.

“In the current part of the beetle flight period, which usually runs from late May to somewhere into July, you know, we would just suggest avoiding cutting green trees,” Moan said. “Unless you’re going to be processing that soon.”

Beetle-killed spruce can be used for firewood and for lumber. Beetles tend to live on the underside of a tree’s bark. Moan said that over time, they’ve served as a natural part of forest ecosystems, making room for healthier younger trees, but many landowners want to manage outbreaks to limit the amount of destruction to their properties. The Division of Forestry and their partners are currently working to develop new tools to help.

Erin McKinstry is Alaska Public Media's 2018 summer intern. She has an M.A. from the University of Missouri's School of Journalism and a B.A. from Knox College. She's reported stories for The Trace, The Midwest Center for Investigative Reporting, Harvest Public Media, the IRE Radio Podcast, KBIA and The Columbia Missourian.

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