Tetropium fuscum (Fabricius) - Fact Sheet


Identification

Adult beetles have a flattened body, 10 to 15 mm long.1, 25, 55, 128 The head is black or dark brown, with a deep longitudinal groove between the antennae. The head is also covered with long, light-coloured hairs.1, 25, 55 Their eyes are completely divided.55 The slender antennae are half the length of the body and are reddish brown.25, 55, 123, 128 The pronotum bulges laterally.19 The elytra are tan, brown, or reddish-brown with 2 or 3 longitudinal grooves.123 The legs are dark brown or reddish-brown.1, 25, 55

Host Trees

Picea (main host), Abies, Pinus and Larix.1, 25, 55, 128 In North America, only Picea has been found infested to date.55

Location of Infestation Within the Tree

Larvae feed on the inner bark and sapwood along the entire stem. However, the lower portions of the bole are the most heavily infested.55, 123, 124

Host Condition

Stressed (e.g. drought, root disease), dying, recently felled, or healthy trees.1, 25, 35, 55, 85 Middle aged and mature spruce trees are preferred.124

Distribution

Europe and Japan. Introduced to North America in Halifax, NS eastern Canada and efforts are being made to prevent further spread.1, 55

Signs and Symptoms

Eggs are laid singly or in pairs in well concealed locations under bark scales or in bark crevices.1, 55

Larvae bore into the inner bark and excavate a network of irregular, 6 mm wide galleries, which become filled with tightly packed, fine-grained frass and short wood fibres.1, 55 Larval galleries lightly etch the sapwood.55 Much of the tree's inner bark can be destroyed by these wide, irregular and meandering larval galleries.55 Mature larvae bore "L-shaped" galleries within the sapwood. Larvae first bore into the sapwood to a depth of about 2 to 4 cm, then turn parallel to the trunk for another 3 to 4 cm.123 These galleries end in an oval-shaped pupal chamber.1, 55

Pupation occurs in the spring either in the bark, between the sapwood and bark or in the sapwood. Pupae lie in a vertical position with their heads pointed upward.85 The wood may be stained from the associated Ophiostoma fungi.55

Adults exit through oval or circular exit holes that are 4 to 6 mm in diameter, which may or may not be plugged with coarse sawdust.1, 55 Attacked trees produce excessive white resin down the length of the trunk.55 Trees may be reinfested over subsequent years.55 Infested tree crowns exhibit progressive yellowing, browning and loss of needles.55 Once the tree has died, the remaining foliage changes to reddish-brown.55

Adult Tetropium fuscum (10-15 millimetre long).
A - Adult T. fuscum (10-15 mm long).
Resin flowing from tree attacked by Tetropium fuscum.
B - Resin flowing from tree attacked by T. fuscum.
Resin flowing from infested tree.
C - Resin flowing from infested tree.
Tetropium fuscum larva.
D - T. fuscum larva.
Irregular shaped Tetropium fuscum larval galleries.
E - Irregular shaped T. fuscum larval galleries.
Tetropium fuscum larval galleries and oval exit hole (4-6 millimetre wide). Note fine-grained frass in larval galleries.
F - T. fuscum larval galleries and oval exit hole (4-6 mm wide). Note fine-grained frass in larval galleries.
Stand mortality caused by Tetropium fuscum.
G - Stand mortality caused by T. fuscum.

Photo credits

  • A Klaus Bolte, Natural Resources Canada, Canadian Forest Service
  • B Canadian Food Inspection Agency, Dartmouth
  • C Bob Guscott, Nova Scotia Department of Natural Resources
  • D Stephanie Sopow, Natural Resources Canada, Canadian Forest Service
  • E Ken Harrison, Natural Resources Canada, Canadian Forest Service
  • F Tom Prest, Canadian Food Inspection Agency
  • G Bob Guscott, Nova Scotia Department of Natural Resources