Infested areas appear swollen and cracked because the sapwood is also destroyed. Numerous holes are visible in heavily infested stock, and frass is usually abundant. Moreover, the wounds caused by the lilac borer allow a wood-destroying fungus, Polyporus vericolor, to enter, producing additional damage. Adults emerge in August and September to mate, and the females lay their eggs on the rough bark or wounds of lilac and privet. As soon as they hatch, the tiny worms bore into the bark.
Contact is maintained with the outside, and frass is expelled through the opening.
Lilac borers overwinter as larvae in the wood, usually near the ground. The following spring and summer, the borers tunnel under the bark and into the wood. The larvae pupate close to the surface. There is one generation per year. Infestation-prone shrubs can be sprayed with a residual pesticide in August to prevent further infestation.