Lead cable borer—Scobicia declivis
Lead cable borer (a false powderpost beetle, family Bostrichidae) is named for its behavior of boring into old, lead-covered electrical and telephone cables. In these situations, it also has been named short-circuit beetle. Lead cable borer is an uncommon pest of damaged tree limbs. Its larvae mostly feed in wood already killed by other causes.
Because they feed hidden in damaged or dead wood, their emergence holes in wood (described below) may be the first indication this beetle is present.
Adults are cylindrical and black to dark brown. They sometimes have a partly reddish prothorax, the enlarged hoodlike feature immediately behind the head that mostly hides the head when seen from above. Adults are 1/4 to 1/3 inch long.
Larvae are up to about 1/3 inch long and cream colored with a small, dark head. They occur in wood and when exposed in their tunnels they commonly have a C-shaped posture. The oblong pupae are about 1/4 inch long and initially whitish but darken and develop appendages before the adult emerges.
Lead cable borer develops through 4 life stages: egg, larva, pupa, and adult. Overwintering and most of the life cycle is spent as larvae in wood. Pupation occurs in late winter to spring. Adults emerge from damaged and dead wood during spring and early summer. Adults chew tunnels into dead or injured wood where the females lay eggs. The larvae chew, feed, and tunnel in wood for about 9 months. Lead cable borer has 1 generation per year.
Adults bore into wood to create tunnels in which the females lay eggs. The hatching larvae chew, feed, and tunnel in limb or trunk wood, which weakens the host's structure. When adults emerge, they leave rounded holes 1/8 to 1/6 inch in diameter in bark and wood.
Provide shrubs, trees, and woody vines with a good growing environment and appropriate cultural care to keep them growing vigorously, which makes them less susceptible to most wood borers. Use good sanitation to manage this pest. Prune out and dispose of dead and dying limbs. Remove and dispose of dead shrubs, trees, and vines. Do not pile dead wood near woody species because these beetles can breed there and emerge to attack nearby plants.
Adapted from Pest Management Guidelines: Grapes and Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).
Tunneling damage of lead cable borer larvae.
Adult lead cable borer, side view.
Adult lead cable borer, top view.