I think Diatomaceous Earth might be a good course of action based on what I have read/heard. It stops insects physically, not chemically. At least that is my understanding. If I where you I would start there before going with anything chemical.
Best advice to date from Gorst Valley Hops: Have a strong Integrated Pest Management plan and be prepared to use it.
That said, I don't know what exactly that is (other than a caterpillar).
Generic google search results: