These invasive, wasp-like insects are eating Pierce County pine trees

Yahoo

02-06-2025

You may notice a pine sawfly on your pine trees this spring or summer. The pesky creatures are more disturbance than damage, but The News Tribune has gathered advice on what to do about them.
A common type of pine sawfly people are likely dealing with in Pierce County is the European sawfly, said entomologist and director of Washington State University's Puyallup Research and Extension Center Todd Murray.
He said he's seen pine hedges in the area being fed on by sawflies, which are a wasp-like insect. They are an invasive species from Europe, and were first documented in Washington state around 2008, Murray said. The sawflies feed on pine needles, sometimes causing bare spots on trees that can be striking, but do not cause critical tree damage, Murray added.
'They aren't really tree killers, they're not a species that's a major concern,' he said. 'They just take the needles away.'
He said pine sawflies also lay their eggs in pine needles, and these egg-positing wounds can be spotted on the foliage. As they get bigger, larvae begin to feed on the needles, making their presence more obvious. Since larvae typically live in big groups, the best way to rid a plant of them is to remove them physically, Murray said.
'They're aggregate feeders, they like to hang out together and eat,' he said. 'If you can reach into bushes within arm's length, you can knock the larvae right off the tree physically, into a bucket of soapy water.'
He said some people may also use insecticide to keep the insects away from their plants, but the bugs aren't deadly to pine trees. Birds are the main predator for pine sawflies, so people can also allow nature to take its course, he added.
For those who feel they have an annual issue with the insects, Murray suggested scouting recent pine needle growth for egg-positing wounds and using that information to see when larvae will eventually develop, to be prepared to remove them.