Branch Borers
Oberea schaumii LeConte and 0. Delongi Knull

Morris, R.C.; Filer, T.H.; Solomon, J.D.; McCracken, Francis I.; Overgaard, N.A.; Weiss, M.J. 1975. Insects and Diseases of Cottonwood. Gen. Tech. Rep. SO-8. New Orleans, LA: U.S. Dept of Agriculture, Forest Service, Southern Forest Experiment Station. 41 p.

Two branch borers attack cottonwood and other poplars throughout much of the United States. Although both species may occur together, 0. delongi is more prevalent in the South, and 0. schaumii is more common further north. Small stems and branches are tunneled and sometimes weakened so that breakage occurs. Terminal breakage often results in crooked trunks, forking, and heavy branching.

Egg niches, the earliest signs of attack, may remain in evidence on stems and branches for several weeks. Later, frass protrudes from the entrance, particularly during attacks of 0. schaumii; 0. delongi ejects little frass. Infested stems may appear swollen. This symptom is most noticeable with 0. delongi, which causes some stems to become greatly enlarged and gall-like. The adults typically feed on the midribs and branch veins of the leaves; such feeding is conspicuous and indicates stem infestation.

Oberea delongi attacks in cottonwood branches. Photo by James Solomon, USDA Forest Service

The adults are elongate long-horn beetles. 0. schaumii ranges from 1/2 to 5/8 inch (12 to 16 mm) in length; 0. delongi is slightly smaller. Both species are variable in coloration. In 0. schaumii the thorax is yellowish to orange with four dark, smooth spots; the wing covers vary from yellowish to black. In 0. delongi the thorax varies from yellowish orange to black, and the wing covers are black. The larvae of both species are legless, narrow, and yellowish white. Larvae of 0. schaumii reach a length of 1/2 to 1 inch ( 12 to 25 mm) ; those of 0. delongi reach 3/8 to 5/8 inch (10 to 16 mm). The pupae of both species are yellowish white.

Adult beetles emerge from April to June and feed on the foliage before laying eggs in niches gnawed in the bark. 0. schaumii selects stems and branches up to 1 1/2 inches (38 mm) in diameter, but 0. delongi prefers smaller stems (usually current year’s growth) up to 1/2 inch (12 mm) in diameter. The eggs hatch in about 2 weeks, and the larvae begin tunneling down the center of the stem. Pupation occurs within the gallery. Adults cut circular holes to exit. The life cycle of 0. schaumii varies from 1 to 3 years; that of 0. delongi is 1 year.

O. delongi adult feeding on cottonwood. Photo by James Solomon, USDA Forest Service

Branch borer damage is usually kept at low levels by natural enemies. Woodpeckers, particularly downy woodpeckers, have been observed to destroy large numbers of 0. delongi larvae in some stands. Larval diseases kill many borers during some years.