Hylurgops palliatus

 
IDENTITY
Name:   Hylurgops palliatus
Pest Authorities:  (Gyllenhal)
Taxonomic Position:  Insecta: Coleoptera: Scolytidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
Synonym(s):
   Bostrichus abietiperda Bechstein
   Hylesinus fuscus Duftschmidt
   Hylesinus marginatus Duftschmidt
   Hylesinus palliatus Gyllenhal
   Hylurgops parvus Eggers
   Hylurgus helferi Villa
   Hylurgus rufescens Stephens
   Ips piceus Marsham
   Ips rufus Marsham
 
RISK RATING SUMMARY
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Uncertain
Uncertainty in this assessment results from: The ability of Hylurgops palliatus to adapt to North American conifers or compete with indigenous bark beetles is unknown. Moreover the pathogenicity of fungi and nematodes, associated with this insect, to North American conifers and their ability to hybridize with closely related North American species has not yet been established.

RISK RATING DETAILS
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 active, directed host searching capability or is vectored by an organism with directed, host searching capability.
  • Organism has high inoculum potential or high likelihood of reproducing after entry.
Justification: Hylurgops palliatus has been collected in traps in Erie County, Pennsylvania, U.S. and may be established in that area. It has also been intercepted many times at ports of entry in both Canada and the U.S. in locations where potentially suitable host material occurs. Its distribution across Eurasia suggests that the climatic conditions prevalent over much of Canada and the U.S. would be suitable for its establishment. Moreover, it has adapted to two North American conifers, Pinus radiata and P. strobus, which have been planted within its natural range. This insect has a high likelihood of reproducing after entry.

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: Like other bark beetles of the family Scolytidae, Hylurgops palliatus is capable of flying at least short distances in search of suitable hosts. Adults are also subject to wind dispersal. The life stages of this insect can be transported over long distances in dunnage, crating, lumber containing bark strips and unprocessed logs. It has been intercepted at U.S. ports of entry on 217 occasions between 1985 and 2000 (Haack 2001). This insect has a high reproductive potential and potential hosts (conifers) have contiguous distributions across many parts of North America. Because of its cryptic nature and similarity in appearance to indigenous bark beetles, infestations might not be detected until they are widespread. This would make eradication difficult, if not impossible. H. palliatus has a broad host range. In addition, several of its known hosts (e.g. Pinus sylvestris, Picea abies) are widely planted in portions of North America in forest and Christmas tree plantations or as ornamental and shade trees.

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.
  • 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.
  • No effective control measure exists.
  • Organism has potential to be a more efficient vector of a native or introduced pest.
Justification: Hylurgops palliatus is not considered a pest of economic importance in its natural range because it confines its attacks to recently dead material. Moreover, species of Hylurgops indigenous to North America are not considered economically important. Provided that it behaves in North America in the same manner that it does in Eurasia, little or no economic impacts are expected.

The major potential economic damage that could be caused by this insect is related to the staining fungi and nematodes that are associated with it. The pathogenicity of these agents to North American conifers is unknown. However if this insect should introduce Eurasian species of pinewood nematodes, Bursaphelenchus spp., into North America and they cause the same level of tree mortality caused to Asian conifer forests following the introduction of the North American pinewood nematode, B. xylophilus, major economic impacts could result.

Environmental Potential Is Low Risk
The relevant criteria chosen for this organism are:  
Justification: By itself, Hylurgops palliatus is expected to have a negligible environmental impact. Although it could displace some indigenous bark beetles, it is expected to be one of a large complex of insects that help decompose dead wood. However, if some of the fungi or nematodes that it vectors are pathogenic to North American conifers, they could cause major ecological disruptions including extensive tree mortality in conifer forests and changes in tree species composition.

 
HOSTS
Hylurgops palliatus breeds in conifers of the family Pinaceae including species of fir, Abies spp., true cedar, Cedrus spp., larch, Larix spp., spruce, Picea spp and pine, Pinus spp. It appears to occur more commonly in fir and spruce and is less common in true cedar, larch and pine (Browne 1968, Grüne 1979, Wood and Bright 1992).

Species of Abies that are known hosts include Abies alba (=Abies pectinata), Abies nordmanniana (=Abies bornuelleriana), Abies cilicica, Abies sachaliensis and Abies sibirica (Balachowsky 1949, Browne 1968, Grüne 1979, Kyvolutskaya 1997, Selmi n.d.).

Known larch hosts include Larix decidua (=Larix europaea), Larix gmelinii and Larix sibirica (Balachowsky 1949, Browne 1968, Grüne 1979, Pfeffer 1995, Winter 1983, Wood and Bright 1992).

Species of spruce attacked by this insect include Picea abies (=Picea excelsa), Picea glehnii, Picea koraiensis, Picea jezoensis (=Picea microsperma), Picea obovata, Picea omorika and Picea orientalis (Balachowsky 1949, Pfeffer 1995, Selmi n.d., Winter 1983, Wood and Bright 1992.)

Pine hosts include Pinus cembra, Pinus heldreichii (=Pinus leucodermis), Pinus mugo var.. rostrata (=Pinus uncinata), Pinus nigra, Pinus nigra ssp. pallasiana, Pinus peuce, Pinus pinea, Pinus pinaster, Pinus radiata (native to North America), Pinus sibirica, Pinus strobus (native to North America) and Pinus sylvestris (Balachowsky 1949, Diaz 1984, Pfeffer 1995, Winter 1983, Wood and Bright 1992).

 
GEOGRAPHICAL DISTRIBUTION
Africa:
      Algeria (Wood and Bright 1992)
Asia:
      China (Heilongjiang Province), Japan, Korea, Russia (Kuril Islands, Sakhalin, Siberia, Ussuri region, West Siberian Plain), Turkey (Choo and Woo 1989, Kryvolutskaya 1997, Legalov n.d., Wood and Bright 1992).
Europe:
     Austria, Belgium, Bulgaria, Caucasus Region, Czech Republic, Denmark, England, Estonia, Finland, France, Germany, Hungary, Ireland, Italy, Latvia, Lithuania, Netherlands, Norway, Poland, Republic of Georgia, Romania, Russia (Leningrad Province), Scotland, Slovakia, Spain, Sweden, Switzerland, Turkey, Former Yugoslav Republics (Balachowsky 1949, Bright and Skidmore 2002, Diaz 1994, Kakulia and Maglakelidze 1973, Mandelshtam 2002, Subansenee 1971, Selmi n.d., Telnov et al. 2001, Turcani and Capek 2000, Wood and Bright 1992).
North America:
     In 2001, Hylurgops palliatus adults were captured in baited funnel traps in Erie County, PA, U.S. (USDA Forest Service 2003).
 
BIOLOGY
The genus Hylurgops consists of 20 known species of bark beetles. Seven species are known from North and Central America and 13 are found in Eurasia (Wood 1982). None of the North American species are considered pests. Hylurgops pinifex, an eastern North American species, breeds in logs, stumps and the basal portions of dead and dying pines, spruce and larch (Drooz 1985, Furniss and Carolin 1977). All species of Hylurgops have similar habits and none are considered important pests. In Germany, Hylurgops palliatus may have one or two generations per year (Grüne 1979) whereas in France, it has two generations. Overwintering adults appear in the spring, sometimes as early as March (Balachowsky 1949).

Adult maturation feeding takes place in the bark of the same host in which they developed. They feed either in individual or collective tunnels (Browne 1968). Flight usually occurs from April -July (Grüne 1979) but adults can be seen until late fall if the temperature is favorable. The spring flight season in Germany was reported as being March-April in some localities and from mid-April-late May in others. In Denmark, studies show a positive correlation between flight activity and temperature. Overwintering adults begin flight in April when the temperature reaches a maximum of 6 to 8 degrees C. Adult flight peaks in late April when maximum temperatures vary from 15-20 degrees C (Subansenee 1971).

If a second generation occurs, adults emerge between July and November or December, with peak emergence taking place in August. Emerging second-generation adults do not fly long distances and overwintered close to where they developed (Subansenee 1971).

Females construct galleries, which are diffuse and wider at the entry orifice. They extend longitudinally between the bark and the cambium. Egg galleries are 3-5 cm long (Balchowsky 1949, Diaz 1994, Grüne 1979). Eggs are deposited randomly in small groups along the gallery in an irregular fashion. Eggs are covered with a fine layer of sawdust in notches cut along the sides of the gallery (Diaz 1994).

The larval galleries are sinuous and entangled, either perpendicular to the wood fibers or oriented in all directions, sometimes engraving the sapwood (Balachowsky 1949, Diaz 1994). In England, larvae are present from May to September (Bevan 1987) and undergo four instars.

Pupation occurs in late summer. Adults emerge in late summer-fall and spend the winter in the soil (Lekander 1968, Balachowsky 1949), under the bark of large trees trunks, or in groups of individuals among sawdust (Diaz 1994).

Hylurgops palliatus prefers moist, shady conditions for breeding sites. Therefore attacks are confined to portions of logs and trees not exposed to sunlight (Balachowsky 1949, Diaz 1994. In a Finnish study of attack density and breeding success at different distances from the edge of a Picea abies forest, H. palliatus was found to breed more successfully at increasing distances from the stand edge and its attack densities increased markedly towards the forest interior. This was attributed to the significant effect of the forest edge on the desiccation of host material (Peltonen and Heliovaara 1999).

 
PEST SIGNIFICANCE
Economic Impact:    Hylurgops palliatus does not attack live trees and has not been reported as a pest of economic importance within its natural range. It breeds in stems and large branches of dying, dead or cut trees, as well as in log piles and prefers logs cut during the fall of the previous year over freshly cut logs (Schroeder and Lindelöw 1989). On rare occasions, it will occupy large roots (Balachowsky 1949). The beetle has been observed in trees infested by more aggressive bark beetles, including Ips sexdentatus and Tomicus piniperda. It appears to favor Norway spruce, Picea abies, which are beginning to deteriorate (Volz 1987).

Hylurgops palliatus is associated with a number of bluestain fungi. Two are Ceratocystis autographa Bakshi and C. penicillata (Grosm.) Siemaszko (Bakshi 1951 and Mathiesen-Käärik 1953 (in Upadhay 1981), both cited Diaz 1994). Neither are known to be primary pathogens.

In England, blue-stain fungi isolated from Hylurgops palliatus trapped in Pinus sylvestris billets consisted of four Leptographium species, including one of unknown identity, and two undescribed species of Graphium. These have been identified as Leptographium procerum, L. truncatum, L. wingfieldii, Leptographium sp. ‘GG’, Graphium sp. A. and Graphium sp. B. (Wingfield & Gibbs 1991). Leptographium procerum (= Verticicladiella procera) has a wide distribution, which includes Europe, New Zealand, and the eastern US and Canada (Ontario and Quebec) (Alexander et al. 1988). It infects the inner bark and sapwood of roots and the lower stem of various conifers, causing basal cankers and tree decline or wilt (Sinclair et al. 1989). The fungus is responsible for white pine root decline, and has caused extensive losses in Christmas tree plantations in Virginia, New York, Pennsylvania, New Zealand and Yugoslavia (Lackner 1984). Pines are the most common hosts but this fungus has also been reported from Pseudotsuga menzeisii, Picea abies and Abies fraseri. L. procerum is known to kill eastern white pine in six states in eastern U.S. from Maryland and Pennsylvania to Indiana (Alexander et al. 1988).

Leptographium truncatum (=? L. lundbergii Lagerberg & Melin), affects Pinus radiata and P. strobus (Eglitis and Pasek 2001). According to inoculation tests, the species is not highly virulent and may be a secondary pathogen (Wingfield et al. 1988). This fungus has also been reported in Ontario where it is not believed to be a strong pathogen (Harrington 1988).

Leptographium wingfieldii is a European species associated primarily with the bark beetle, Tomicus piniperda but has also been reported in association with Hylastes opacus and Hylurgops palliatus. This fungus has recently been isolated from logs of Pinus sylvestris infested with Tomicus piniperda in southern Ontario. Although its role as a tree pathogen has not been defined, it causes staining in trees attacked by T. piniperda. Mass inoculum experiments have demonstrated its pathogenicity at high inoculum density, causing mortality of healthy Pinus sylvestris (Jacobs & Wingfield 2001, Solheim et al. 1993). It has been suggested that L. wingfieldii may play a role in overcoming the resistance of trees under beetle attack (Solheim and Långström 1991).

No observations have been made yet on the pathogenicity of the as yet undescribed species of Leptographium and Graphium species isolated from Hylurgops palliatus in England. The same is true for Cylindrocarpostylus gregarious, redescribed after having been rediscovered from individuals and galleries of bark beetles, including H. palliatus (Kirschner and Oberwinkler 1999). Other fungi found in Europe in association with this insect or its galleries for which there is no information regarding pathogenicity include Chionosphaera cuniculicola, Ophiostoma neglectum, Atractocolax pulvinatus and Phialocephala trigonospora, (Kirschner and Oberwinkler 1998, Kirschner and Oberwinkler 1999a, 1999b, Kirschner et al. 1999, Kirschner et al. 2001).

Hylurgops palliatus has also been found to carry dauerlarvae of the pinewood nematodes Bursaphelenchus mucronatus, B. poligraphi, B. eggersi and B. sexdentati (Braasch et al. 1999, Braasch et al. 2000). None of these nematodes are known to occur in North America. Both B. mucronatus and B. sexdentati are pathogenic to various degrees, depending on the origin and virulence of the strains, the susceptibility and age of the tree species and the environmental conditions. The host trees most susceptible to B. mucronatus are Pinus sylvestris, P. pinaster and Larix deciduas. B. sexdentati is reported from P. sylvestris, P. pinaster, P. halepensis and P. nigra. Different strains of B. mucronatus did not cause death to 11-29 year old pine trees in Germany and Austria but pathogenic strains are believed to contribute to pine decline in areas of low precipitation and mean July/August temperatures of between 20-25 degrees C. A preliminary risk assessment of B. mucronatus concluded that its establishment in southern Europe of pathogenic strains together with a suitable vector may represent a risk to and P. nigra. As for B. eggersi and B. poligraphi, pathogenicity tests carried out in Europe by inoculation on 3-year-old plants of Pinus, Picea, Abies, Larix and Pseudotsuga in climate chambers and in the field showed that they did not cause mortality of the experimental trees (Braasch et al. 2000). Five additional species of nematodes have been reported from the Republic of Georgia on Hylurgops palliatus and its frass collected from Picea orientalis. These are: Parasitorhabditis palliati, Cryptaphelenchus cryptus, Mikoletzkya palliati, Panagrolaimus fuchsi and Cephalobus persegnis (Kakulia and Maglakelidze 1973). Little is known about these nematodes. Therefore, their importance as potential pathogens cannot be assessed.

Environmental Impact:   Hylurgops palliatus is one of a complex of cambium and wood boring insects instrumental in the decomposition of dead wood. There are no reports in the literature of any detrimental environmental effects of H. palliatus.

Control:    Species of Hylurgops are not considered pests of economic importance and, therefore, no control measures have been developed. However, good sanitation and stand management is probably the best approach. All dead host material should be removed to deprive the beetle of places to breed. This approach is not feasible however in natural (i.e. unmanaged) areas. Debarking and treatment of wood material by kiln-drying or with an approved fumigant or insecticide spray at prescribed rates in the originating country and/or at the port of entry should reduce likelihood of introduction. Infestations in export logs may be minimized by a rapid turnover of log stockpiles in the forest or in log yards (Bain 1977).

 
DETECTION AND IDENTIFICATION
Symptoms:    Symptoms of attacks include reddish colored boring dust on the bark surface of infested trees and logs and characteristic galleries in the cambium region.

Morphology:    Eggs are a pearly white color. Larvae are white, c-shaped, legless grubs with an amber colored head capsule. Larvae are similar to the closely related species, Hylurgops glabratus from which it can be distinguished by its smaller size and other minor characteristics. The pupae are white, mummy-like and have some adult features including wings that are folded behind the abdomen.

Adult are superficially similar to other Scolytidae of the subfamily Hylesininae. The head, underside of body and edges of elytra are blackish, the remaining parts brown, dark brown or reddish-brown in color (Balachowsky 1949, Grüne 1979). They are about 2.5-3.4 mm long with a broad thorax that narrows down at the front (Bevan 1987). The head is usually visible from above. Eyes are entire and not divided.

Testing Methods for Identification:    Examination of adults by a taxonomist with expertise in the family Scolytidae is required for positive identification.

 
MEANS OF MOVEMENT AND DISPERSAL
Adults are capable of flying up to 11.5 m above ground to suitable sites but most (84%) fly below that height, as demonstrated by a Swedish study (Byers et al. 1989). They are capable of flying several km. in search of suitable hosts are also subject to dispersal by winds. Untreated solid wood packing material is the most important pathway for long distance spread of Hylurgus palliatus as evidenced by numerous interception records of this pest since the 1970's, on pallets, crating and dunnage at ports of entry in the U.S., New Zealand and Canada (CFIA 2001, Haack 2001). H. palliatus is one of the most commonly intercepted Scolytidae at U.S. ports of entry. Between 1985 and 2000, it was intercepted 217 times (Haack 2001).

 
BIBLIOGRAPHY
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AUTHOR(s)
Name(s):
Louise Dumouchel
 
 
Name and Address of the First Author:
Louise Dumouchel
Plant Health Risk Assessment
Canadian Food Inspection Agency
3851 Fallowfield Road
Nepean, Ontario
Canada K2H 8P9
 
CREATION DATE:        05/12/03
MODIFICATION DATE:        05/06/04