The changing behavior of several insects is a growing concern for foresters, a University of Idaho Extension expert says.

Chris Schnepf, extension forestry educator in Post Falls, attributes the “atypical” behavior to changes in climate, calling it “global climate weirding.”

Moths in the Cydia laricana complex kill the tops of sapling larch trees. They were first recorded in Montana 100 years ago, but were never seen in Idaho until 2020, when they were found at several sites, Schnepf said.

Larch has been planted heavily throughout the state, as the top performer in dealing with root diseases, which are the biggest threat to forest health, Schnepf said.

“Douglas fir and grand fir are super vulnerable to root diseases; larch is our species that’s best capable of dealing with it, so it gets planted a lot,” he said. “So to see sapling larch that are just getting off the ground have tops be killed by this moth. … If you’re a forester and you’ve planted larch seedlings, that’s pretty painful to see.”

University and state entomologists are assessing the situation, Schnepf said.

“It’s a moth that’s never been seen in Idaho,” he said. “It could have been here and we didn’t see it.”

The moth isn’t the only insect that’s learned a new trick.

The pine engraver beetle normally survives for two generations a year. But in recent years, it’s lasted for three generations.

“If three is the new normal, that starts to affect what we do on the ground,” Schnepf said.

The beetles will emerge and attack standing green trees left after a timber harvest.

Fire seasons average a month longer than normal, which means a longer growing season for some bark beetles species, Schnepf said. Farther south from Idaho, they can produce as many as four generations, he said.

Forest density and species composition tend to drive insect and disease issues and forest fire concerns, Schnepf said.

“It’s not a cure, but generally speaking, if you reduce stand density and favor larch and pine instead of Douglas fir and grand fir, that deals with a lot of the insect and disease issues that tend to be most problematic,” he said.

https://www.idl.idaho.gov/wp-content/uploads/sites/116/2020/02/Cydia-Fact-Sheet-508cjw.pdf