Invasive sawfly identified in Sitka

SITKA — An invasive species has been discovered in Sitka, but biologists said they don’t expect the destructive insect to cause the same harm to alders in southeast Alaska as it did farther north in the state.


The green alder sawfly is native to Europe, East Asia and North Africa. It was first positively identified in Alaska in 2009, according to the Daily Sitka Sentinel.

By the time it was identified, the sawfly was actively defoliating thin-leaf alders along riverbeds in Anchorage, Seward, Kenai and in the Matanuska-Susitna area, according to the Cooperative Extension Service. Anchorage’s Ship Creek has been particularly hard hit, said Bob Gorman, a CES agent in Sitka.

“It’s pretty well cleared out of alder,” Gorman said.

The extension service was notified about the Sitka presence of the green alder sawfly after Michelle Putz with the U.S. Forest Service noticed one of her red alder trees didn’t look healthy.

“I was thinking, ‘Why does my tree look so bad?’” Putz said.

Turns out the tree was covered with hundreds of the pale-green caterpillar-like insects. She called Gorman, who went to Putz’s property to see for himself.

“It was, like, whoa,” Gorman said.

Putz destroyed the tree to keep the insects from spreading.

The larval stage of the insect resembles a caterpillar, according to the extension service.

In spring, the larvae pupate and change into winged adults that resemble some wasps. Within two weeks of emerging, the larvae feed on alder leaves. They mature in six weeks.

Gorman he doesn’t believe the sawfly poses the same threat to the Sitka alder as the thin-leaf alder in Anchorage and farther north.


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