Forest Pests: Insects, Diseases & Other Damage Agents

Balsam Shootboring Sawfly
Pleroneura brunneicornis Rohwer

Hanson, T., and E. B. Walker. [n.d.] Field guide to common insect pests of urban trees in the Northeast. Waterbury, VT: Department of Forests, Parks and Recreation.

Hymenoptera: Xyelidae Hosts: Balsam, Fraser and white fir Evidence: Larvae tunnel into the center of new shoots, causing the needles to turn red and die. Initially, the affected shoot has a flattened appearance and just the center turns red (a). As the shoot elongates, the dead tip becomes more obvious and looks much like frost damage. Unlike with frost, the dead tip is easily pulled off, revealing a white larva or hollowed-out shoot (b,c). After the larvae leave the shoots (by mid-June in northern New England) the affected part usually drops. Damage tends to be heaviest in even years. Life Cycle: The sawflies overwinter as either larvae or pupae in earthen cells in the soil. Adults, which emerge in early spring, lay eggs through the bud sheath before buds swell. Upon hatching, the young larva feeds toward the tip of the shoot in the needle cluster. Later, it burrows into the shoot and tunnels towards its base. When mature (6-7 weeks), the larva crawls out of the shoot, burrows into the ground, and spins a thin cocoon. In more northerly regions, the insect may spend nearly two years in the cocoon.	a. Early sign of damage by BALSAM SHOOTBORING SAWFLY.
	b. BALSAM SHOOTBORING SAWFLY larva feeding on developing shoot.
	c. BALSAM SHOOTBORING SAWFLY adults emerge in early spring and lay eggs through the bud sheath before buds swell.

Management: Since damage is rarely heavy in consecutive years, control measures are not usually necessary. However, repeated damage from this insect has resulted in unmarketable trees in some plantations. In a year with normal to above normal temperatures, the sawfly does poorly on balsams that break bud early so it tends to attack late-breaking balsam fir or Fraser fir. Conversely, in years when cool weather slows bud development following adult emergence, damage to balsam tends to be similar to that of Fraser. In mixed plantations of Fraser and balsam, the insect shows a decided preference for Fraser fir during most years. Keeping trees healthy and tightly sheared, where appropriate, will help minimize damage caused by this insect. This pest is most prevalent in areas adjacent to native balsam fir stands.

References:

Drooz, A.T. 1985. Insects of Eastern Forests. USDA Forest Service Miscellaneous Publication 1426. p 378;

Johnson, W.T. and Lyon, H.H. 1991. Insects That Feed on Trees and Shrubs. 2nd edition. Cornell University Press. p 20;

Martineau, R. 1984. Insects Harmful to Forest Trees . Agriculture Canada Government Publishing Centre, Supply and Services, Ottawa. p 103;

Rose, A.H. and Lindquist, O.H. Revised by Syme, P. 1994. Insects of Eastern Spruces, Fir and Hemlock. Canadian Forest Service Publication. p 38-39.

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