Not sure I can help you Martin, but a few years back in my old garden I planted a small Scots Pine. Each spring/early summer however the tree would become infested with hundreds of caterpillars which swarmed around the new needle growth and devoured them completely. They were clever little blighters though because they never ate enough to bring about the demise of the tree, just make it look awful. I once physically shook the tree to detach them and they spread all over the surrounding lawn. Undeterred however they all immediately turned heel and headed straight back for the trunk of the tree.I'm sure they all had little evil grins on their faces.