Bronze Birch Borer
Hosts: White, cutleaf and yellow birch are preferred but other birches are also attacked.
Evidence: Look for top dieback, with first symptoms including sparse, chlorotic foliage. Welts appear on the surface of the stem above borer galleries (a). Adult emergence holes are D-shaped and about 1/8 inch long. Adults are dark green-bronze or copper-bronze and about 3/8 inch long. Larvae are flat-headed borers with two spines at the posterior end.
Life Cycle: It takes one to two years to complete development. Winter is spent in the larval stage in tunnels beneath the bark. Depending on location, adults emerge from early spring through August. They feed on leaves for several weeks before laying eggs on unshaded bark. Newly-hatched larvae bore into the cambium, and then make galleries that are tightly packed with frass and zig-zag across the wood grain (b).
Management: Weakened or injured trees are preferred by this pest, but healthy trees are also attacked. Trees which have been recently transplanted or those on stress-prone sites are especially susceptible. Numerous galleries can girdle the tree, causing branch dieback. Infestation and dieback tend to start at the top of the tree and move down. Prune off dead and dying branches before adults emerge in early spring. Maintaining or improving vigor of trees through proper fertilization, watering, and control of defoliators can help reduce attack. Chemical controls are generally not effective by the time a problem is detected.
Figure a: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Figure b: E. Bradford Walker, Vermont Department of Forests, Parks and Recreation, Waterbury, VT.
Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 277-278;
Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 272-273;
Martineau, R. 1984. Insects Harmful to Forest Trees. Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 131-133;
Rose, A.H. and Lindquist, O.H. 1982. Insects of Eastern Hardwood Trees. Canadian Forest Service Publication, Forestry Technical Report 29. p 95-96.