Sugar maple borer

Damage by the sugar maple borer (Glycobius speciosus) varies among forest types and stands within a type. Infestation rates, the proportion of damages stems per acre or hectare, range from less than 5 to nearly 50 percent. Sugar maples in all stands are susceptible, but the incidence of damage is highest in stands with high proportion of sugar maple. Rarely does sugar maple borer kill a tree, but it directly affects the main part of the stem, sometimes reducing the available space for tapping. Borer attack is most prevalent on trees of low vigor.

Damage also is important because a successful; attack results in the partial girdling of the tree and the possible death of portions of the crown. Silvicultural practices that maintain tree vigor are essential, and early thinnings should include the removal or previously attacked trees.

The adult sugar maple borer (Fig. 56) is a black beetle marked with bright yellow bands of varying width and shape like a W. The borer is 0.8 to 1.0 inch (20 to 25 mm) long and belongs to a group commonly referred to as longhorn beetles, a name evoked by the pest’s unusually long antennae.

The sugar maple borer deposits one to several eggs in crevices or holes that it chews through the bark, usually on the lower 20 feet (6 m) of the trunk. Following egg hatch, the small larva enters the tree and feeds beneath the bark.

During the second year of its 2-year life cycle, it excavates a shallow transverse or oblique feeding gallery in the outer wood and inner bark. As a result of this girdling (similar to the damage caused by an axe blaze or logging scar), large branches above the gallery may be killed. A large open scar of exposed wood often results (Fig. 57), and a significant portion of the trunk may be rendered unusable for tapping. Large, open wounds are conspicuous, but scars from the sugar maple borer often are difficult to detect as the damage is hidden beneath slightly cracked and loosened bark (Fig. 58). The larval gallery deeply engraved on the surface of the exposed wood distinguishes scars caused by sugar maple borer from those caused by other agents.

During its first year, gallery direction changes from transverse to vertical. Eventually, the off-white, grub-like larva (Fig. 59) excavates an oval overwintering tunnel (Fig. 60) 0.4 to 0.6 inch (10 to 15 mm) in diameter that penetrates the wood to a depth of 2.0 to 4.0 inches (5 to 10 cm).

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