Anything that would stop, "bugs" eating your shrub would be detrimental to the butterfly larva. Are you sure it's not butterfly caterpillers. A search in the evening with a flashlight might turn up slugs or snails, (hand picking is involved) Enjoy Rai

A lot of times if you have holes in the leaves and can't see any bugs it is earwigs. They feed at night. Insectigone (diatomatious earth) sprinkled around the bottom of the plant will help control them and shouldn't harm the butterflies or their larva