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Warren's root collar weevil,
Hylobius warreni,
Tree Species Attacked: Lodgepole pine is the most common host, followed by interior spruce. Usually, only trees over 2 cm in diameter at the root collar are attacked.
Insect Description & Damage Symptoms: Larvae are large (up to 2 cm in the final instar), legless, and creamy white. The heads are orange-brown. The flightless adults are typical weevils with a prominent, curved snout. They are 1.0 to 1.5 cm long and thick-bodied, with dull, black-flecked colouring and grey-white scales. Infested plantations display random mortality of single or small groups of trees. Damaged trees exhibit straw-coloured to deep red foliage starting with the older needles, and stunted terminal growth. Damaged trees are usually easy to push over or have an obvious lean. Positive identification requires careful examination of the tree root collar. During feeding, larvae tunnel into the phloem and cambium and slightly into the wood of the root collar area. Damage is always associated with large quantities of resin mixed with the soil surrounding the damaged roots, which the larvae form into tube-like shelters. This mixture usually feels crunchy if crushed during root collar examination. Pupation occurs at the end of a pitch tunnel sealed off to form a pupal cell.
Damage: Larvae are responsible for the majority of the damage. Young trees may be completely girdled at the root collar and die. Older trees are often partially girdled at the root collar, and may be completely girdled around some of the roots; however, no mortality results. Significant damage often occurs when a young stand is located adjacent to an older infested stand, particularly if the young stand opening is small, as the flightless adults usually only move a maximum of 13 m per year. In addition to direct mortality, damaged trees may suffer growth loss and increased susceptibility to root rot, blue-stain fungi, windthrow, and snow press. No pre-weakening of host trees is required for attack, and studies indicate that weevil populations increase as duff depth increases.
Similar Damage: Basal feeding by small mammals such as voles and hares, as well as death due to stem rust or root disease, may be initially confused with Warren's root collar weevil. The tube-like shelters and resin-soaked soil protecting the larvae will distinguish the root collar weevil.
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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 February 18, 2002 |
