Gooseberry Sawfly

Not an orchard-fruit pest as such, but returned this week to find one of my gooseberry cordons almost entirely stripped of its leaves by sawfly larvae (variety: Invicta). I haven't had this problem for over ten years, and I wonder if it might be related to the fact this is the first year for many we have no blue tits nesting in our boxes. Another cause might be that this rather middle-aged plant is a little stressed by intensive cordon-culture, as there is also a bad aphid infestation of new growth.

I think we'll just have to live with it as I don't particularly want to spray. I'm not a huge fan of culinary gooseberries and I've never had the problem on Whinham's Industry, the only other variety I grow.