STEM BORER


 

A stem borer in the genus Oberea is a sporadic pest of blueberries, huckleberries, azalea, rhododendron, and laurel. This species (or a close relative) occurs throughout much of the eastern United States (Craighead 1949).

The adult stage of the stem borer is a slender, elongate beetle with a light brown or yellowish body. There are two dark spots on the dorsal surface of the thorax and a dark lateral margin on each wing cover. Beetles are about 15 mm in length (5/8 inch) and have slender antennae that are nearly as long as the body. The larval stage lives only within the stem or crown of its host plant; it has a legless, cream-colored body with a dark brown head and mouthparts. A distinctive patch of tiny, dark colored spines is present on the upper surface of the body just behind the head. Larvae reach a length of about 3 cm (1.25 inches) when fully grown.

Illustrations:

  • Adult stage of the blueberry stem borer.
  • A distinctive mound of frass accumulates beneath a borer-infested cane.
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    Life Cycle and Seasonal Distribution


    In early summer, adult females lay eggs individually under a flap of bark cut near the terminal end of a blueberry cane. Larvae hatch in about two weeks. At first, the larvae tunnel upward within the cane (often killing the terminal), then reverse direction and burrow toward the crown of the plant. From 5 to 25 cm (2 to 10 inches) of the stem may be excavated during the first year. Larvae become inactive with the approach of winter, but resume feeding in the spring. After reaching the crown of the plant, they move to adjacent stems, continue feeding for the rest of the year, and complete development during the spring of the third year (Driggers 1929).

     

    Symptoms and Damage


    In some cases, stem borers cause extensive damage by destroying the growing tips or by killing entire canes. However, in other cases, infested plants seem to suffer very little injury. Recent infestations are often difficult to detect, but as larvae grow and begin to tunnel downward in the stem, they periodically chew open small holes in the bark. Pellets of light yellow frass are ejected from these holes during the summer and accumulate in distinctive mounds on the ground beneath the plant.

     

    Natural Enemies


    In the southeastern United States, stem borers in the genus Oberea have been reported as hosts of a tachinid fly (Lixophaga variabilis) and a braconid wasp (Bracon ceramycidiphagus). There is no evidence that either parasite is an important biological control agent (Linsley 1961).

     

    Scouting, Management, and Control


    Stem borers are usually not a frequent or widespread problem in commercial blueberry fields. Beginning in mid-summer, infested plants can be spotted easily by looking on the ground for characteristic mounds of frass. Stem borer injury can be minimized by removing infested canes or wilted terminals as soon as larvae are detected. Cut the stems well below their hollow section to insure that larvae will never reach the crown of the plant.


    References

  • Craighead, F. C. 1949. Insect enemies of eastern forests. USDA Misc. Publ. 657. 679 pp.
  • Driggers, B. F. 1929. Notes on the life history and habits of the blueberry stem borer, Oberea myops Hald., on cultivated blueberries. J. New York Entomol. Soc. 37: 67-73.
  • Linsley, E. G. 1961. The cerambycidae of North America. Part I. Introduction. Univ. Calif. Pub]. Entomol. 18: 1-135.

  • Last updated: 5 June 1997
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