Before I start treating I'd want to identify the culprit. You could wind up killing beneficial insects and doing nothing to stop the damage. Could you take some photos of the damage, what parts are chewed up? Do you see anything that might give you a clue what is doing the damage?
With hostas my first thought is slugs. Does it look like slug damage? Are they coming out at night and hiding during the day? Can you see slime trails? You might put some beer in a shallow container at night and see if any drown overnight. Or look with a flashlight after dark.
It's a little early in the season but grasshoppers or blister beetles can cause problems. Maybe some other chewing insect. Can you see any black bits that might be insect poop?