It is important to find the culprit so that an effective control can be found. Usually with hostas the culprit is slugs or snails. There is a natural control called Sluggo which works as a bait for these pests. There is also a product with orthoboric acid in a bait form that is also considered more "environmentally friendly".
The damage may also be caused by grasshoppers, caterpillars, or beetles. If you can catch them in the act and submit another question I can provide a more targeted response. You may need to go out there at night with a flashlight as some pests are nocturnal. Turn leaves over in the search.
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