Hardy hibiscus recurring problem
This looks like damage by the hibiscus sawfly. The photos are out of focus and we cannot say what the white substance is and the black may be frass.
The adult sawfly is a small black fly and the larvae are pale green. The larvae feed on the foliage. Look for this. You can handpick if the infestation is light or spray with horticultural oil. Follow all label directions and do not spray in high temperatures. See our website for photos and more information http://extension.umd.edu/hgic/sawflies-flowers