Warren Root Collar Weevil

Warren root collar weevil is a beetle that is indigenous to coniferous forests in North America. It extends throughout most of the forested areas in Canada, from Newfoundland to coastal British Columbia and into the southern part of the Northwest Territories and the Yukon.

Description

Warren root collar weevils are dark in colour, relatively large (13.0 mm and 13.7 mm long for males and females, respectively) and flightless.

The hosts of the Warren root collar weevil include most pine and spruce trees native to Canada, as well as some exotic species, but lodgepole pine, jack pine (Pinus banksiana) and white spruce (Picea glauca) are preferred.  White spruce and black spruce (Picea mariana) are usually attacked if they occur intermixed with lodgepole pine. Less frequent hosts include western white pine (Pinus monticola), and Engelmann (Picea engelmannii) and Sitka (Picea sitchensis) spruces.

Oviposition occurs from late May to early September with a peak oviposition period in July.  The larval stage causes the most damage, and is the most easily identified indicator of an attacked tree.  The larva is a white legless grub with a brown head capsule.  The larval stage is parasitic on the live host tree, feeding in below-ground galleries present in the bark and cambial tissues of the root collar and roots, sometimes causing extensive damage.  It is only when the weevil girdles the complete circumference of the tree that host mortality occurs.

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 5-20 year old trees. Severely affected trees of this age class exhibit 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. A planting delay of two to three years in areas where large pre-harvest weevil populations were present may reduce the impact of the weevil in susceptible stands.  Prescribed burning or scarification may also to reduce weevil populations.

References

Borror DJ, DeLong DM, and Triplehorn CA. 1976. An introduction to the study of insects. 4th ed. New York; Chicago; San Francisco; Atlanta; Dallas: Holt, Rinehart and Winston. 852p.

Cerezke HF. 1974. Effects of partial girdling on growth in lodgepole pine with application to damage by the weevil Hylobius warreni Wood. Canadian Journal of Forest Research. 4:312-320.

Cerezke HF. 1994. Warren root collar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae), in Canada: Ecology, behaviour, damage relationships and management. Canadian Entomologist 126: 1383-1442.