Trees, Shrubs and Conifers: Gone 3 days, worms ate my tree, 2 by Pistil

Pistil wrote:
Thanks VV-
Once you got me going, I found it. These are Pristiphora geniculata, the Mountain-ash Sawfly (there are a lot of sawfly species). They are originally from Europe. They were identified for me by our local Ag Extension agent/Master Gardeners group. I have uploaded photos in Bugfiles. They are new in the Pacific Northwest- first noted in my county in 2009. Nobody is attempting any kind of control. I am worried about the native Sorbus species around here, and a bit worried about the Sorbus aucuparia that has naturalized. It is really nice to see all the berries this time of year. I planted this sapling because I missed one that was in my yard. I had to remove it for some rock walls I had put in. The birds missed it too. It seemed like an easy choice-it was easy and pest free. I think I chopped it down in 2009...
Hmmm. Now it is hard to know what to do. If the sawfly invasion has begun, maybe I should cut my losses and give up now. Meanwhile, I stomped on a half dozen more that hatched out.