Bob, I have read that spider mites are often a cause of leaf damage in butterfly bushes. These are really tiny little things that are reddish in color. They're so small that you might not even see them on the leaf. Take a white sheet of paper and hold it under a few leaves. Try to knock mites off the underside of the leaves. You should see little red specs on the paper.

If that's what you see, try an insecticidal soap or horticultural oil. Both should help get rid of them.

Good luck! I'm curious if that's what it is.