Trees, Shrubs and Conifers: Gone 3 days, worms ate my tree, 0 by Pistil

Pistil wrote:
Aagh. It was fine when I left. They ate all the new growth. I just planted this Mountain ash sapling this summer (Sorbus aucuparia, I think). I had one here before that I really liked, as did the birds, so I assumed it would be pest free. These little buggers reared up and glared at me when I approached. I cut off the leaves they were on and threw them away.
But, now what do I do?
I assume it will probably recover, but am not sure, it was already pretty stressed by being planted in summer, and was slightly scorched. If this will happen every summer I should just plant something else there instead.
What do you all think?