My rhubarb is always being munched on by something, these days usually the sheep. However, back in the days when the animals didn't have any access to it, something was still eating it and I believe it was cabbage moth grubs. I've learned the last few years, that it's not just your cabbages you have to protect from these. I had a couple in my persimmon fruit this year. Usually they only get mealy bugs. I found the cabbage grubs or whatever they were only ate the leaves, they left the stalks alone. If it's the stalks that are being eaten, let me know and I'll see if I can find one of my books. In 6 years, I've only ever had problems with the leaves being eaten (except now, the sheep loves the stalks just as much as the leaves, which has left me with not much!!!).
When you signed off on your message I thought at first it said 'Wallace and Grommit'!!
Jane