Plants > Plant Pests > Brown Spruce Longhorn Beetle  

Tetropium fuscum (Fabricius) - Brown Spruce Longhorn Beetle

BACKGROUND:

In March, 1999, the brown spruce longhorn beetle (BSLB), Tetropium fuscum  was found in dying red spruce trees in Point Pleasant Park, Halifax, Nova Scotia. The following summer, the Canadian Forest Service (CFS) reared over 40  T. fuscum adults from red spruce bolts collected in the park. Subsequent investigations by the CFS concluded that T. fuscum was also attacking apparently healthy trees. Specimens collected in the park in 1990, originally identified as a related native species (Tetropium cinnamopterum) have also now been confirmed as Tetropium fuscum.

HOSTS:

Spruce (Picea spp.) trees are the main hosts of BSLB. On occasion, firs ( Abies spp.), pines (Pinus spp.) and larches (Larix spp.) may be attacked.

DISTRIBUTION:

This insect is native to Europe, where it can be found from Scandinavia to Turkey.It is also known from Japan and western Siberia. The find in Nova Scotia is believed to be the first discovery in North America.

BIOLOGY:

In the spring, female beetles lay eggs in the bark of standing or recently felled trees. Eggs are usually laid singly, but sometimes in clusters of up to ten eggs. Larvae hatch 10 to 14 days later, and bore into the phloem to feed, producing a network of irregular tunnels packed with sawdust-like frass (excrement). After about two months, the larvae are 1.5 to 2.5 cm long. They bore into the sapwood perpendicular to the trunk, for about 2-4 cm cm. They then turn and tunnel parallel to the trunk for another 3-4 cm. This forms a characteristic L-shaped tunnel, where the larva changes to a pupa. The adults emerge in about 14 days, chewing a round or oval exit hole in the bark about 4-6 mm in diameter. The adults live approximately three weeks and can be found from June to August. Both males and females are strong flyers.  Larvae overwinter just under the bark in the phloem / cambium layers.

Over most of the range of spruce in Canada, the BSLB would likely have one generation per year (egg, larva, pupa, adult).

DETECTION & IDENTIFICATION:

Damage:

In its native range BSLB, is recognized mainly as a secondary forest insect, attacking trees that have already been subjected to other types of insect attack or environmental stresses. During a population outbreak, beetles can attack living, healthy trees. Outbreak levels have the potential to persist for a decade and continually cause damage over extensive tracts of vulnerable conifer forest. In Europe, T. fuscum often attacks stands of Norway spruce over 50 years of age. Tunnels in the wood as a result of larval feeding reduce timber quality.

Symptoms of attacked trees include:

• Streams of resin scattered along the trunk (Figures 3 & 4 )
• Holes in the bark about 4 mm across
• Networks of feeding tunnels just under the bark, up to 6 mm across, filled with sawdust-like material
• Tunnels in the wood about 4 cm deep and 6 mm wide. These tunnels appear L-shaped when the wood is cut longitudinally.
• Coarse sawdust may be found in and around tunnels or plugging the entrance/exit hole

Identification:

• Adult (Figures 1 & 2): Flattened body, 1 to 1.5 cm long. Head and neck area dark brown to black. The elytra (wing covers) can be tan, brown or reddish brown and have 2 to 3 longitudinal stripes. The antennae are red-brown and about half of the body length. The legs are dark brown.
• Egg: one mm long, oblong and white with a tinge of green.
• Larva: Yellow-white, about 14 to 28 mm long, and slightly flattened. The head is reddish brown and about 3 mm wide.
• Pupa: White, 10 to 17 mm long and 3.8 mm wide.

Click on image for larger view
Fig. 1. Female	Fig. 2. Male	Fig. 3. Resin flow	Fig. 4. Resin flow

Other Links

• Natural Resources of Canada, The Canadian Forest Service
• Nova Scotia Department of Natural Resources

Text: Plant Health Survey Unit.
Photos : Natural Resources of Canada, Canadian Forest Service