Adult rhododendron borers active in May and June, are small black moths with white and yellow markings. These moths lay their eggs on the bark of rhododendrons, azaleas, and mountain laurels. Tiny caterpillars hatch from the eggs, bore into the sapwood, and develop into inch-long "worms." The boring by the caterpillars may cause the stem to wilt. If the stem is large enough it may not wilt. However, sometimes the first indication of rhododendron borer infestation is that the stem breaks off. Pruning and destroying heavily-infested parts of the plants is component of the management for this pest.
From: Steve Bambara, Extension Entomologist, NCSU