Rose of Sharon Buds Being Chewed?

Something is eating the tips of my rose of Sharon buds. I've sprayed with Sevin and pulled all the chewed buds off the bush. All the new buds that grow are being chewed and never bloom. The leaves are healthy and there's lots of new growth on the bush. I've opened a chewed bud to see if there is an insect inside. Nothing. What's the problem

By Tim