Tetropium fuscum

Name:   Tetropium fuscum
Pest Authorities:  (Fabricius)
Taxonomic Position:  Insecta : Coleoptera : Cerambycidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
   Brown spruce longhorn beetle (English)
   Longicorne brun de l’epinette (French)
   Tofarget granbarkbukk (Norwegian)
   Callidium fuscum Fabricius
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Certain
Establishment Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism has successfully established in location(s) outside its native distribution
  • Suitable climatic conditions and suitable host material coincide with ports of entry or major destinations.
  • Organism has demonstrated ability to utilize new hosts
  • Organism has high inoculum potential or high likelihood of reproducing after entry.
Justification: Tetropium fuscum was introduced and became established in eastern Canada in Halifax, Nova Scotia ca. 1990. The main area of infestation is Point Pleasant Park but infestations have also been detected outside of the Park. This insect is believed to have arrived in Halifax at least 10 years prior to its discovery via dunnage, wood packing material, or pallets on board ships coming from the insect’s home range. Point Pleasant Park is adjacent to the container terminal of the Port of Halifax, where this wood packing material is piled on site (Anon 2000). Other species of Tetropium have been intercepted in wood products entering North America, Europe and South America.

Spread Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is capable of dispersing more than several km per year through its own movement or by abiotic factors (such as wind, water or vectors).
  • Organism has demonstrated the ability for redistribution through human-assisted transport.
  • Organism has a high reproductive potential
  • Potential hosts have contiguous distribution.
  • Newly established populations may go undetected for many years due to cryptic nature, concealed activity, slow development of damage symptoms, or misdiagnosis.
  • Eradication techniques are unknown, infeasible, or expected to be ineffective.
  • Organism has broad host range.
Justification: Adults are strong fliers and could travel distances of at least 2-3 km in search of hosts. This insect has a high reproductive potential and a broad host range. The potential North American hosts of Tetropium fuscum, especially species of Picea, have contiguous distributions across the boreal forests of Canada, the northeastern U.S. and Alaska. Newly established populations of exotic Tetropium spp. could go undetected for long periods. For example, it is believed that the infestation of T. fuscum in eastern Canada may have arrived at least 10 years prior to its discovery (Anon 2000).

Economic Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism attacks hosts or products with significant commercial value (such as for timber, pulp, or wood products.
  • Organism directly causes tree mortality or predisposes host to mortality by other organisms.
  • Damage by organism causes a decrease in value of the host affected, for instance, by lowering its market price, increasing cost of production, maintenance, or mitigation, or reducing value of property where it is located.
  • Organism may cause loss of markets (domestic or foreign) due to presence and quarantine significant status.
  • No effective control measure exists.
Justification: Within its natural range, Tetropium fuscum attacks weakened, dying or recently felled trees and is normally resisted by healthy, vigorous trees. However, where it has been introduced into Canada, it attacks and kills apparently healthy spruce. Spruce accounts for about 60% of the forest volume in Nova Scotia and 33% across Canada. Therefore the spruce dominated boreal and montane forests of North America are potentially threatened by this insect.

The total shipment of conifer (softwood) lumber from Canada for destinations abroad was valued at $ 12.48 billion (CAD, 1997; Natural Resources Canada 1998, pp. 22). About 74% of these exports are to the U.S. At high population levels, attack by native Tetropium spp. can render the timber useless because of the high density of larval borings (Safranyik and Moeck 1995). In Ontario, the devaluation in lumber grade in spruce and pine amounts to about 10% during the first year of attack and up to 20% during the second year (Gardiner 1975). Gardiner (1975) estimates a 35% value loss could occur in white spruce.

Environmental Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is expected to cause significant direct environmental effects, such as extensive ecological disruption or large scale reduction of biodiversity.
  • Introduction of the organism would likely result in control/eradication programs that may have potential adverse environmental affects.
Justification: Justification: Wood boring insects are instrumental in decomposition of dead and dying trees, logging residues and stumps. Tetropium fuscum can kill trees and, therefore, change species composition of forests in favor of non-host species. The presence of Tetropium fuscum in North America could greatly reduce the number of spruce, which can grow to large sizes and live for several hundred years. Red spruce, Picea rubens, is the provincial tree of Nova Scotia, and is therefore an acknowledged symbol and key component of its forests.

Introduction of an exotic species of Tetropium may have effects on the community ecology of native species of bark beetles and woodborers, including native Tetropium spp. At the present time, no native Tetropium species have been found in Point Pleasant Park, Halifax Nova Scotia where T. fuscum has become established. This raises the possibility of competitive displacement of native species.

Increased activity of indigenous insects and the hazard of wildfires of increased frequency and severity could occur in North American forests as a result of increased tree mortality caused by establishment of this insect.

Control and eradication programs could lead to undesirable environmental impacts associated with chemical or mechanical treatments.

Tetropium fuscum attacks conifers, primarily spruce, Picea spp., pine, Pinus spp. and fir, Abies spp.

In Europe, Norway spruce, Picea abies; Sitka spruce, Picea sitchensis; blue spruce, Picea pungens; Scotch pine, Pinus sylvestris and silver fir, Abies alba are known hosts. Larches, Larix spp., are also occasionally attacked (Juutinen 1955).

In Nova Scotia, Canada, where Tetropium fuscum has become established, the favorite host is red spruce, Picea rubens. Infestations have also been detected in white spruce, Picea glauca, black spruce, Picea mariana and Norway spruce (Smith and Humble 2000).

     In Asia, Tetropium fuscum is known to occur in Japan (Anonymous 1989), Turkey (Schimitschek 1944), and is uncommon in western Siberia (Schwenke 1974, Novak et al. 1976, Cherepanov 1990).
     This insect occurs in northern (Lappland) and central Europe and the forests of the Ural Mountains of Russia (Schimitschek 1929, Vité 1952, Schwenke 1974, Cherepanov 1990, Bense 1995), Slovenia and Bosnia-Herzogovina (Mikšic 1963).
North America:
     Tetropium fuscum was introduced and became established in eastern Canada at Halifax, Nova Scotia ca. 1990.
The genus Tetropium is a large genus of conifer infesting longhorned woodborers. Members of this genus are found in conifer forests of Asia, Europe and North America. Several species are reported capable of killing living trees and one species, T. fuscum, has recently become established near Halifax, Nova Scotia, Canada. Species indigenous to North America include: T. cinnamopterum and T. velutinum, which occur both in eastern and western North America, T. schwarzianus from eastern Canada and T. abietis and T. parvulum in western North America (Knull 1946, Furniss and Carolin 1977).

The life cycle of Tetropium castaneum is generally staggered over a one to two year period depending on climate and nutritional requirements (Juutinen 1955, Schwenke 1974, Johansson et al. 1994). In mild climates, most of the population develops over one year throughout Europe (Novak et al. 1976) and a small portion of the population requires two years to complete development. In colder climates, such as Siberia, most of the population requires two years to complete a generation (Cherepanov 1990, Juutinen 1955).

The larval stage is the typical overwintering stage. However adults may also overwinter (Vité 1952, Schwenke 1974, Novak et al. 1976).

The adults live about three weeks, but emergence is staggered so that they are present any time from May to August (Novak et al. 1976). Warm, calm and sunny days are preferred for flight activity (Novak et al. 1976). Flight in Tetropium castaneum generally does not occur below about 12ºC to 14ºC and warm summer temperatures of 19ºC to 24ºC are preferred (Dourojeanni 1971, Dourojeanni and Falisse 1970). First flight is observed between 240 and 300 degree-days accumulated above 5ºC in one year and the peak of flight activity generally occurs at about 450 degree-days above 5ºC (Dourojeanni 1971). At temperatures below 5ºC, egg development ceases (Juutinen 1955).

Adults are sexually mature immediately after emergence from the host and copulate for a short period of time (generally minutes). Typically, wind thrown trees, lightning damaged trees exposed to fire and freshly cut logs are attacked. The chemical ecology for this species is not well known. More general biological information about cerambycids can be gleaned from Gressitt (1959) and Hanks (1999). A few days after mating, the female lays an average of 100 eggs (range 80-150), usually singly, or sometimes in clusters of up to 10 eggs underneath the bark scales or in fresh crevices in the bark of hosts (Juutinen 1955; Schwenke 1974). Microsculptures on the egg’s surface may capture gut symbionts for the larva.

Larvae hatch after a period of 10-14 days and feed directly on the woody tissue. They feed in the cambium and produce an extensive network of wide, irregular tunnels, which are densely filled with sawdust and excrement. Larval development is complete after about two months of feeding (Novak et al. 1976). Mature larvae construct a horizontal gallery into the wood to a depth of about 2 to 5 cm and continue boring vertically for another 3-4 cm. vertically to form a hook-like gallery. At the end of this gallery, the larva constructs pupal chamber. The mature larva prepares a bed of frass for a pupation site and plugs the entrance to the pupal chamber with frass.

At pupation the head of the larva points towards the plug. Pupation lasts about 14 days (Schwenke 1974). The pupal chamber is constructed near the phloem and xylem interface only during heavy attacks on Picea abies (Novak et al. 1976). In central Europe, the brood adults emerge at the end of the summer from elliptical holes about 5 mm in diameter (Cherepanov 1990). These are the new generation that will produce overwintering larvae. At average July and August temperatures greater than 20ºC, a generation of Tetropium fuscum, a related species, requires about 120 days for completion. However, if average July and August temperatures are less than 20ºC, then one generation takes about 360 days to complete (Schimitschek 1929). Larvae overwinter in the wood or near the bark as dictated by environmental or nutritional conditions.

There are natural biological control agents that already occur in Canada which are known to attack T. fuscum such as the parasitic wasps, Rhyssa persuasoria (L.) (Schimitschek 1929), and possibly Rhyssa lineolata (Kirby) and Rhimphoctona macrocephala (Provancher), and woodpeckers. The latter two parasitoids were reared from red spruce logs associated with T. fuscum infestations in Point Pleasant Park or near Halifax, Nova Scotia (Andy Bennett, Agriculture and Agri-food Canada, pers. comm. 2005). These biological mortality factors may reduce beetle populations (Vité 1952; Schwenke 1974), but their impact on the T. fuscum population in Halifax has not been determined.

There are also many other natural enemies in Eurasia that are known to attack T. fuscum (Schimitschek 1929; Vité 1952; Juutinen1955; Demelt 1966) and these include:

Ichneumonidae: Townesia tenuiventris (Holmgren), Dolichomitus dux (Tschek.), Dolichomitus terebrans (Ratzburg), Dolichomitus tuberculatus (Geoffroy), Neoxorides collaris (Gravenhorst), Odontocolon spinipes (Gravenhorst), Odontocolon dentipes (Gmel.), Xorides ater (Grav.), Xorides brachylabris (Kriechbaumer), Xorides irrigator (F.), Xorides praecatorius (F.) and various Campopleginae such as Rhimphoctona obscuripes (Holmgren), Rhimphoctona megacephalus (Gravenhorst) (Andy Bennett, Agriculture and Agri-food Canada, pers. comm. 2005).

Braconidae: Atanycolus initiator (Fabr.), Atanycolus neesi Marsh., Atanycolus sculpturatus (Thoms.), Doryctes mutillator (Thunb.), Doryctes obliteratus (Nees), Wroughtonia dentator (F.) (Henri Goulet, Agriculture and Agri-food Canada, pers. comm. 2005).

Tachinidae: Billaea triangulifera Zett.

Known predators include: Laphria gilva [Choerades gilva] (Lavigne et al. 2000; CABI 2005), Thanasimus spp., Athous subfuscus Müll., Raphidia spp., Phaoestigma notata F., Inocellia crassicornis Schummel (Vité 1952), Palloptera usta Meig., and numerous woodpeckers (Juutinen 1955).

Economic Impact:    In Europe, Tetropium fuscum is a pest of Norway spruce. Typically, windthrown trees, trees damaged by lightning or exposed to fire and freshly cut logs are attacked. This species can build up to damaging populations, especially in forests weakened by defoliating insects (Juutinen 1955). T. fuscum is capable of attacking and killing relatively vigorous trees within its natural range but is recognized primarily as a secondary forest insect (Juutinen 1955, Lottyyniemi and Uusvaara 1977, Lucht and Klausnitzer 1998).

Within its natural range, the primary economic impact of Tetropium fuscum is loss of wood quality and market value of conifer logs. In European forests Tetropium fuscum and other species of Tetropium cause about 40% loss in volume in young stands and about 30% in mature stands (Novak et al. 1976). Exit holes leave trees susceptible to secondary infection by various fungi or other pathogens. This can further diminish timber values (Juutinen 1955).

Recreation and aesthetic values could be severely affected in urban or park-like settings if outbreaks occur. The death and removal of large specimen trees in these settings has an impact on the users, which far outweighs the commercial value of such trees.

Environmental Impact:   Wood boring insects are instrumental in decomposition of dead and dying trees, logging residues and stumps. Tetropium fuscum can kill trees and, therefore, change species composition of forests in favor of non-host species. Moreover, tree mortality caused this insect can result in wildfires of increased frequency and intensity because of elevated fuel levels in forests.

Control:    In Nova Scotia, attempts are underway to eradicate infestations of Tetropium fuscum by cutting and burning of infested trees. In some parts of its natural range, T. fuscum causes enough damage to require direct control. Control measures make use of silvicultural tactics designed to improve overall forest health and vigor. These include cutting and elimination of all infested trees, use of trap trees subsequently treated with chemicals and treatments with chemical and biological insecticides

No chemical pesticides are currently registered for direct control of Tetropium spp. in North America.

Symptoms:    In Nova Scotia, where Tetropium fuscum is an aggressive tree killer, symptoms of attack include streams of resin flow down the trunk emitted from larval entrance wounds, ovoid adult exit holes about 4 mm in diameter and the presence of dead and dying spruce trees.

Morphology:    The egg is 1.0-.2 mm long and 0.2-0.3 mm wide and oblong and oval in shape. Color is white with a tinge of green. The generally smooth egg bears a band of microsculpture about 20% of the length of the egg, towards the end with the head of the developing larva. Differentiation among eggs of various species of Tetropium is not possible (Schimitschek 1929).

The larva is yellow-white in color, with conspicuous legs on the thorax, the tarsi of which bear tiny spinules (Schimitschek 1929). Mature larvae are about 14-28 mm long, and are slightly flattened. The head is about 0.8 mm wide (Švácha and Danilevsky 1987, Cherepanov 1990). Hairs on the sides of the head are sparse and the head is reddish brown in color. The head capsule bears a narrow lateral white band, typical of the genus. Long, but sparse setaceous hairs (about 10 to14 hairs per tuft) occur in the anterior half with a sclerotized base. The lateropraesternum is entirely reticulately microspiculate, without a large central smooth area (Švácha and Danilevsky 1987). Sclerotized spinules occur on the posterior margin of abdominal tergum IX, which look like spots and are separated by a space greater than the diameter of the spinule. The spinules are set on their tubercular base with extensive, but indistinct sclerotization (Cherepanov 1990).

The pupa is white in color, about 17 mm long (range 10-17 mm) and about 3.8 mm wide (Schimitschek 1929, Cherepanov 1990). The mesonotum is slightly raised and is devoid of large spinules. The pronotum bulges and is rounded laterally, narrowing more anteriorly (i.e., the sides become parallel), with a short longitudinally grooved fold along the sides of the disk, and minute uneven spinules. In the region of the scutellum, the mesonotum is slightly raised and minute spinules occur that are barely visible under high magnification. The abdominal tergites bulge in the posterior half, with acute spinules along the sides of a common longitudinal groove forming a transversely elongate band that narrows laterally. Tergum VII has minute spinules behind the middle form an indistinct transverse row.

The adult is black or dark brown, with a flattened body that varies in length from 8-17 mm (Novak et al. 1976, Villiers 1978, Bense 1995). The elytra range in color from brown to reddish or yellow-brown or straw-yellow and bear 2 to 3 distinct longitudinal stripes (Bense 1995, Novak et al. 1976, Cherepanov 1990). A broad whitish to beige pubescent band is present at the base of the elytra (Cherepanov 1990) and the 5th sternite is distinctly truncated (flat edge). Short gray-yellow densely packed hairs cover the first quarter of the elytra. The short antennae are red-brown in color and the legs are dark brown and short. A deep groove is found on the head between the antennae. The mat-like pronotum is almost as wide as it is long. Viewed from the side, the pronotum is angular and wide, with dense granulation. It also bears a dense, wrinkled and punctured plate that has a longitudinal hole (Novak et al. 1976). The pronotum is usually black with a notable bulge and sometimes with a rusty border at the base and apex (Cherepanov 1990). Fine short hairs cover the body and various diverse forms in color and size occur (Villiers 1978).

Testing Methods for Identification:    Examination of adults by a taxonomist with expertise in the family Cerambycidae is required for positive identification to species. The adults and larval galleries have sufficient characteristics to permit entomologists to make field identifications at least to genus.

Adults are strong fliers and could travel several km in search of suitable host trees.

All life stages could be moved via unprocessed logs, lumber, wooden crating, pallets and dunnage. The borings may be blocked by frass and difficult to detect. Other species of Tetropium have been intercepted at international ports of entry and T. fuscum is established in the vicinity of Halifax, Nova Scotia, Canada (Anon 2000). All interceptions and introductions of Tetropium spp. have been via wood products in international trade.

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Erhard John Dobesberger
Name and Address of the First Author:
Erhard John Dobesberger
Science Division
Canadian Food Inspection Agency
3851 Fallowfield Road
Ottawa, Ontario
Canada K2H 8P9
CREATION DATE:        12/23/02
MODIFICATION DATE:        10/17/05

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