White Pine Weevil

The white pine weevil, a native of North America, is a very serious pest of white pines. Other trees that bear the most serious attacks are Norway spruce and jack pine; trees that are commonly attacked are pitch pine, Japanese red pine, western white pine, limber pine, foxtail pine, and red spruce; Scotch pine, western yellow pine, mugho pine, and black spruce sustain occasional attacks. They stunt and disfigure trees in the forest as well as those grown for ornamental purposes. The weevils prefer small trees (3 to 15 feet tall) and seldom attack trees growing in the shade of other trees.

Description and Life Cycle

The weevils are often hard to find but their damage – die back of the leader – is  easy to spot. Adult weevils are about ¼ inch long and light reddish-brown with several patches of white on the wing covers. Like most weevils, adults have a long snout-like beak from which arise knobbed antennae. The larvae, which are found under the bark of the dying leader, are white, legless, C-shaped, and have brown heads.

Adults overwinter in ground litter and resume activity in April. In early to mid- April, adult females climb to the leaders of trees to feed through small holes chewed in the bark. Eventually, they will insert eggs into these feeding wounds. The larvae hatch in about a week and feed just below the bark. The larvae mature and pupate in mid-July. The  pupae rest in cells carved into the sap wood and lined with straw like sawdust. Adults emerge in late July and early August and feed on the upper tree branches, making small puncture wounds. As winter approaches, the adults return to the litter to hibernate.

Damage

The weevils feed on the bark tissue of the terminal shoots. Adult females climb to the leaders of trees to feed through small holes chewed in the bark. This feeding causes sap to run down the leader. The larvae continue to feed downward, girdling and killing the shoot as they go. As the terminal is girdled, the new shoot of the current year's growth withers and the tip bends over and turns brown. This stage of damage usually becomes noticeable about mid-June. Examination of the dead shoots will show the white larvae or pupae beneath the bark or in the wood and pitch. That year's growth is always killed, but two or three years of growth are commonly killed. The result is forked and crooked trees.

Control

All controls should be targeted to kill the adults or larvae before the tree leaders are damaged. Mechanical control: Prune infested leaders as soon as they droop, cutting the leader out just below where the bark discoloration stops. Do not throw this pruned leader on the ground as some of the weevils may survive. If the damage is stopped before the first whorl of branches is reached, a new leader can be easily trained.

Chemical control: Spraying with insecticides on the spring is the most commonly used technique. Look for the sap flow coming from leaders in early to mid-April. This indicates that the adults are feeding and sprays should be applied immediately. Systemic insecticides are often more effective because they kill any larvae that may already be inside the leader.

Adapted from: University of Connecticut Integrated Pest Management Program; University of Maine Cooperative Extension, 1999; Ohio State University Extension