3 years ago I had sawfly on my gooseberry bush for the first time. The bush must be not much short of being 100 years old. lots of delicious fruit every year until then. I've tried removing them, spraying with soapy water, using a bug spray, and thinning out the plant. Nothing seemed to work. 2 years ago I had such a small crop it wasn't worth picking. Last year there were 3 gooseberries, and this year, despite spraying with nematodes, there were none, and the sawfly caterpillars were more prolific than ever, even spreading to my redcurrant bush.
I'm tempted to just get rid of the bushes altogether if I can't find a prevention.