Warren root collar weevil

Hylobius warreni

Warren root collar weevil is found in the coniferous forests of North America. The weevil's range extends from Newfoundland to coastal British Columbia and into the Northwest Territories and the Yukon.

On this page

• Description
• Host tree species
• Damage symptoms
• Management
• Identification images

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Description

Warren root collar weevils are dark in colour, relatively large (about 13.5 mm long) and flightless. Females lay eggs between late May and early September with a peak period in July. 

The larvae are a white legless grub with a brown head capsule. The larval stage causes the most host damage and is the most easily identified indicator of an attacked tree. The larvae doesn't always kill the tree but feed in below-ground galleries present under the bark of the root collar and roots. It's only when the weevil girdles the complete circumference of the tree that host mortality occurs.

Host tree species

The hosts of the Warren root collar weevil include most pine and spruce trees native to Canada. Lodgepole pine, jack pine and white spruce are preferred. White spruce and black spruce are usually attacked if they occur intermixed with lodgepole pine. Less frequent hosts include western white pine, and Engelmann and Sitka spruces.

Damage symptoms

Pitch exuded by an attacked tree is mixed with particles of the chewed off bark and soil to create a protective covering, which looks pinkish-brown when fresh and eventually hardens into a black mass. Weevil-attacked trees are easily recognizable by the presence of this protective covering below the soil surface at the base of the tree or on major roots.

Tree mortality can occur if one or more larvae completely girdle the tree. Young plantations with small-diameter trees have the highest risk of mortality. Weevil attacks are most evident on young trees, from 5-20 years in age. Severely affected young trees can suffer from above ground growth reduction and decreased root diameter growth.

Management

Warren root collar weevils can live as long as five years, and this longevity is a concern during regeneration of host trees.

Where large weevil populations are present, a planting delay after harvest of two to three years may reduce the impacts. Prescribed burning or soil mixing may also to reduce weevil populations.

Identification images

Characteristic adult root collar weevil larva freshly dug-out of pitch mass at the bottom of a host tree.

Larva

Warren root collar weevil larvae construct a protective covering from pitch, bark, soil, and frass. The larval tunnel is often visible if the pitch mass covering is broken open.

Further reading

Read more about the warren root collar weevil in the Field Guide to Forest Damage in B.C. (PDF, 6.6MB)