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Poplar and willow borer, Cryptorhynchus lapathi
 
 

Fig. 354
Adult poplar and willow borer.
Fig. 355
Poplar and willow borer larvae in willow stem.
Fig. 356
Crown symptoms of trees damaged by poplar and willow borer.
Fig. 357
Poplar and willow borer emergence holes on willow stem.
Fig. 358
Stem damaged by poplar and willow borer.

DISTRIBUTION: This species was introduced into North America from Europe. In B.C., it is most common on Vancouver Island, and the southern interior valleys. Farther north, it is found south of 57 degrees north latitude, and populations are limited primarily to Bella Coola, Skeena, and Nass river valleys, and the northern Fraser River drainage around Prince George.

TREE SPECIES ATTACKED:
Willow is the preferred host, but this borer also attacks poplar species (mainly black cottonwood, balsam poplar, and hybrid poplars). Trembling aspen and paper birch are rarely attacked.

WHAT TO LOOK FOR: Upper crown or whole tree broken over or dead; irregular splits and holes in the bark, through which red-brown and white shavings exude; piles of shavings around the base of the stems.

INSECT DESCRIPTION & DAMAGE SYMPTOMS: Larvae are C-shaped, legless grubs. Their body is creamy-white with a brown head. They are about 1.3 cm long when mature. Adults are stout weevils with long curved snouts, and are 0.8 to 1.0 cm long. Their body is predominantly black, and their back is densely covered with tiny black and either grey or pink scales, which form an irregular band. The life cycle takes up to three years, with the first winter spent as a young larva. Females oviposit during the summer in deep holes chewed in the bark on the lower part of the stems. The young larvae burrow in the inner bark at first, then enter the wood, where they excavate extensive, meandering tunnels, pushing the borings to the outside of the stem. Current damage by the larvae is indicated by irregular splits and holes in the bark of host trees, through which sap and moist red-brown and white shavings exude, and by piles of shavings around the base of the stems. If infested stems are split open, larvae and their tunnels are visible. Previously infested stems are indicated by the presence of circular (0.3 to 0.4 cm diameter) emergence holes, darkened weathered tunnels, and calluses over injured areas. Most damage is done by the larvae, and attacked trees normally range from 2 to 8 cm in diameter. Adults also cause some injury by feeding on branches and on main stems, showing a preference for young succulent bark.

DAMAGE: Larval feeding weakens the stems of host trees, making them susceptible to breakage. Damage to hybrid poplar plantations is of most concern. Clones range from resistant to highly susceptible, and damage is the greatest on trees 2 to 3 years old. This insect can also pose problems in a nursery setting.

SIMILAR DAMAGE: The damage is similar to that caused by the poplar borer, but the poplar borer prefers trembling aspen.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136


Last updated April 23, 2002