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FS ShieldForest Health Protection, Southern Region


Agrilus bilineatus (Weber)

Importance. - This borer attacks red and white oaks throughout the East. Trees weakened by drought, insect defoliation, or other factors are most susceptible. Larvae mine the cambium, resulting in girdled trees. Mortality can be extensive in weakened stands.

Identifying the Insect. - Adult beetles are about 1/5 to 1/2 inch (6 to 12 mm) long, slender, and black, with a light yellowish stripe on each wing cover. Larvae are white, slender, flattened, and about 1 inch (25 mm) long, with two spines at the rear end.

Larvae in galleries

Larvae in galleries. (Click for detail. JPG 34K).

Identifying the Injury. - Larvae excavate winding mines in the inner bark and outer sapwood of the main trunk and large branches, frequently girdling the tree. Attacks usually begin in the upper tree canopy and extend downward as the tree continues to weaken. D-shaped adult emergence holes are evidence of infestation.

Biology. - Adults emerge during spring and early summer and deposit eggs in bark crevices. Eggs hatch in 10 to 14 days. The larvae burrow through the bark and cambium. They overwinter in cells in the bark and pupate the follwing spring. There is one generation per year.

Control. - Control is mainly a matter of preventing attacks through cultural practices that promote tree vigor. Spraying to protect foliage from insect defoliators is recommended in some areas.