Western balsam bark beetle

  • Latin name: Dryocoetes confusus Sw.
  • French name: Scolyte du sapin de l'Ouest
  • Order: Coleoptera
  • Family: Curculionidae
Description

Distribution

British Columbia

The range of the western balsam bark beetle overlays that of its primary host, alpine fir, stretching south to Arizona and New Mexico, and east into western Alberta.

Micro-habitat(s)

Bark, Trunk

Damage, symptoms and biology

During the year following a successful beetle attack, the tree’s foliage changes from green to a bright brick red colour. This red foliage may be retained for up to five years. Accurate assessment of current mortality is therefore only possible if aerial surveys are followed by ground-truthing. Field observations suggest that the majority of attacks occur above 2 m on the bole.

The most conspicuous sign of recent successful attack is a mixture of boring dust and fecal matter (frass) found in bark fissures and at the base of the bole.

Although occasionally D. confusus infestations can kill high numbers of trees in a stand in a single season, successive years of aerial mapping surveys have shown that, more frequently, less than 5% of a stand is attacked in any one year. High beetle populations can persist within a stand for many years until all of the mature and semi-mature alpine fir have been killed.

Description
Egg: Small; pearly-white; oval.

Larva: 3-4 mm long; head pale tan; body yellow-white, curved and wrinkled.

Pupa: 3-4 mm long; yellow-white, with many of the adult parts recognizable.

Adult: 3-4 mm long; mature adult dark brown, with erect red-brown hairs; front of female entirely covered with a dense brush of short red-yellow hairs; front of male sparsely covered with long, red-yellow hairs.

Life history
Adult beetles emerge in late May or June when the temperature within the stand reaches about 15oC, and the flight period may last until the end of July.

The insect normally requires two years to develop from egg through to adult, but given the right climatic conditions there is evidence to suggest that the beetle can complete its life cycle in a single year.

Other information

Dryocoetes confusus is closely associated with a phytopathogenic lesion-causing fungus, Ceratocystis dryocoetidis. The fungus is carried on special repositories called mycangia, located on the beetle’s thorax. Ceratocystis dryocoetidis is responsible for an estimated 65% of the mortality associated with D. confusus. Though initial beetle attacks are often pitched out by the tree, the fungus may be successfully introduced into the phloem, causing subsequent beetle attacks to meet with little or no resistance. Coalescing lesions caused by the fungus may also girdle and kill the trees without any further beetle activity.

Canadian Forest Service Publications

Western balsam bark beetle

Diet and feeding behaviour

  • Phloeophagous : Feeds on phloem.
Information on host(s)

In addition to alpine fir, the beetle also occasionally attacks amabilis fir, Abies amabilis. Rare instances of attacks to white spruce, Picea glauca, and Engelmann spruce, P. engelmannii, have also been recorded.

Main host(s)

Subalpine fir

Secondary host(s)

Amabilis fir, balsam fir, Engelmann spruce, white spruce

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