Warren root collar weevil

Distribution

Canada

Micro-habitat(s)

Twig, Root collar, Root

Damage, symptoms and biology

Warren root collar weevil damage is caused by the larvae, which construct tunnels beneath the bark of the roots and root collar of conifers. Damage by feeding larvae causes resin flows at the base of the tree. The resin forms masses with debris on the ground around the tree, resulting in dirty whitish masses. Lifting these pitch masses reveals the galleries constructed by the larvae.

The insect attacks both young and mature trees. Mortality occurs in young trees when the galleries completely circle the base of the trunk or when, if severely weakened, they become vulnerable to windfall. On mature trees, the galleries rarely circle the trunk, but large roots may be completely girdled, especially near the fork. Repeated attacks of mature trees result in growth loss, but rarely cause tree mortality. However, the trees become more susceptible to disease, such as decay fungi, which accelerates their decline.

The adults emerge from the pupal cells in the fall or spring and crawl up the trunks to feed at night on the bark of the upper surface of small branches. They also feed on the bark of the roots. The adults live up to five years, but the larvae generally complete their development in two years. Generations overlap, with the insect overwintering either in the larval or adult stage. The adults overwinter in the humus at the base of the trees.

Life cycle (East of the Rockies)

Other information

Warren root collar weevil is native to North American conifer forests and is well established in Canada’s boreal forest. It occurs primarily on trees growing in moist sites where the soil is covered with a deep layer of humus or plant debris.

Warren root collar weevil feeds on all native species of pine and spruce, as well as exotic species. In natural forests, its preferred hosts are jack pine, lodgepole pine (in western Canada) and white spruce. First reported in Canada around the 1930s, it has since ravaged pine plantations in eastern Canada, particularly in Ontario, Quebec and Newfoundland.

To protect trees from an outbreak, remove the humus (which retains moisture and serves as an overwintering site for adults) near the collar and large roots, remove and burn all affected trees on infested sites, prune trees that have reached 2 cm in diameter to up to 1 m in height, avoid planting susceptible species in moist soils or near already infested areas, and remove all plant debris from the ground prior to planting.

Main host(s)

Jack pine, lodgepole pine, Norway spruce, red pine, scots pine, white spruce