I've got the same problem, but most of my bushes are defoliated- they move quick. I tried the manual removal (mushing them one by one) early in the year, but even killing dozens of worms per bush is a losing battle.

From what I've read, BT will not kill them, as they are not true caterpillars. Spinosad and insecticidal soaps are what I see commonly mentioned.

I'm interested in hearing from anyone who has dealt with them successfully.

You are going to have to read your labels; I don't think a BT strain has been developed yet to control sawflies.

Birds do not eat these pests, but certain wasps do, if you see any wasps patrolling around the gooseberries, they are beneficial. Some wasps can detect eaten leaves from a great distance.

Repeated and heavy spraying by mid-spring is about the only effective control, once an infestation has occurred, future covering of the plants will not help as next year's flies are already pupating in the soil beneath the plants.

My gooseberry plant is currently half-defoliated, as are others in the neighborhood.

What puzzles me is where it came from and why this year. I have my garden at this location from 2007. I bought the plants currently infected in 2009. I bought them half-price, because they were defoliated!) . So that was first time I saw it without leaves. And since that time - for 5 years - no issues at all. This year it started with my miniature pine tree(growing problem-less since 2007). It lost about all its needles, but I didn't pay much attention why. And now it is on Gooseberry. From what I found in the internet, the pests are Pine sawfly and Gooseberry sawfly. But why they suddenly appeared this year? Are they the same bugs, or conditions of this year juts favorable for pests in this family?

I've replied on your other thread. But as to where it comes from - I find it comes and goes. About 10 years ago it nearly defoliated my Gooseberries but hasn't recurred since (fingers crossed).

I control them with a mixture of green soap (liquid soap avail in Sweden) and water and sometimes chilli / use a spray bottle or garden spray. works like a charm.

Info on pacpackaging

Green Soap Contains:
Saponify pine oil 15-30%, perfume <5%. pH around 10,5. Natural and effective all-purpose cleaner. Soap is a pure natural product made from real pine oil. Soap is effective while being gentle on the surface and the environment. Grumme soap is suitable for cleaning almost all materials and surfaces in all rooms. Eco-labeled. Think, every day you can contribute to a better environment!