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Datasheet

Bursaphelenchus xylophilus
(pine wilt nematode)

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Datasheet

Bursaphelenchus xylophilus (pine wilt nematode)

Summary

  • Last modified
  • 28 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Preferred Scientific Name
  • Bursaphelenchus xylophilus
  • Preferred Common Name
  • pine wilt nematode
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Nematoda
  •       Family: Parasitaphelenchidae
  •         Genus: Bursaphelenchus
  • Summary of Invasiveness
  • B. xylophilus on its natural hosts behaves like other members of the genus, living a mycophagous life cycle on trees weakened or damaged by other causes. When introduced into new continents, it encounters new h...

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Pictures

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PictureTitleCaptionCopyright
Bursaphelenchus xylophilus (pine wilt nematode); SEM showing the spicule (centre) which identifies the species, a destructive pinewood nematode. Original x 5000.
TitleSEM
CaptionBursaphelenchus xylophilus (pine wilt nematode); SEM showing the spicule (centre) which identifies the species, a destructive pinewood nematode. Original x 5000.
Copyright©USDA-ARS
Bursaphelenchus xylophilus (pine wilt nematode); SEM showing the spicule (centre) which identifies the species, a destructive pinewood nematode. Original x 5000.
SEMBursaphelenchus xylophilus (pine wilt nematode); SEM showing the spicule (centre) which identifies the species, a destructive pinewood nematode. Original x 5000.©USDA-ARS
Bursaphelenchus xylophilus (pine wilt nematode); distinctive spicule of male nematode. USA.
TitleMale
CaptionBursaphelenchus xylophilus (pine wilt nematode); distinctive spicule of male nematode. USA.
Copyright©A. Steven Munson/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); distinctive spicule of male nematode. USA.
MaleBursaphelenchus xylophilus (pine wilt nematode); distinctive spicule of male nematode. USA.©A. Steven Munson/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); vulva flap of female nematode. USA.
TitleFemale
CaptionBursaphelenchus xylophilus (pine wilt nematode); vulva flap of female nematode. USA.
Copyright©A. Steven Munson/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); vulva flap of female nematode. USA.
FemaleBursaphelenchus xylophilus (pine wilt nematode); vulva flap of female nematode. USA.©A. Steven Munson/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); tail of male, showing characteristic spicule. Japan.
TitleMale
CaptionBursaphelenchus xylophilus (pine wilt nematode); tail of male, showing characteristic spicule. Japan.
Copyright©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); tail of male, showing characteristic spicule. Japan.
MaleBursaphelenchus xylophilus (pine wilt nematode); tail of male, showing characteristic spicule. Japan.©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); gravid female. Japan.
TitleFemale
CaptionBursaphelenchus xylophilus (pine wilt nematode); gravid female. Japan.
Copyright©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); gravid female. Japan.
FemaleBursaphelenchus xylophilus (pine wilt nematode); gravid female. Japan.©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); general features of head region. Japan.
TitleFeatures
CaptionBursaphelenchus xylophilus (pine wilt nematode); general features of head region. Japan.
Copyright©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); general features of head region. Japan.
FeaturesBursaphelenchus xylophilus (pine wilt nematode); general features of head region. Japan.©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); tee mortality on Mason pine (Pinus massoniana), caused by the nematode. Anhui Province, China.
TitleField symptoms
CaptionBursaphelenchus xylophilus (pine wilt nematode); tee mortality on Mason pine (Pinus massoniana), caused by the nematode. Anhui Province, China.
Copyright©William M. Ciesla/Forest Health Management International/Bugwood.org - CC BY-NC 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); tee mortality on Mason pine (Pinus massoniana), caused by the nematode. Anhui Province, China.
Field symptomsBursaphelenchus xylophilus (pine wilt nematode); tee mortality on Mason pine (Pinus massoniana), caused by the nematode. Anhui Province, China.©William M. Ciesla/Forest Health Management International/Bugwood.org - CC BY-NC 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); pine wilt symptoms, one year after death of tree. USA.
TitleField symptoms
CaptionBursaphelenchus xylophilus (pine wilt nematode); pine wilt symptoms, one year after death of tree. USA.
Copyright©USDA Forest Service/Region 2- Rocky Mountain Region/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); pine wilt symptoms, one year after death of tree. USA.
Field symptomsBursaphelenchus xylophilus (pine wilt nematode); pine wilt symptoms, one year after death of tree. USA.©USDA Forest Service/Region 2- Rocky Mountain Region/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); symptoms in a field setting - note dead trees and browning of foliage on others. China
TitleField symptoms
CaptionBursaphelenchus xylophilus (pine wilt nematode); symptoms in a field setting - note dead trees and browning of foliage on others. China
Copyright©Juan Shi/Beijing Forestry University/Bugwood.org - CC BY-NC 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); symptoms in a field setting - note dead trees and browning of foliage on others. China
Field symptomsBursaphelenchus xylophilus (pine wilt nematode); symptoms in a field setting - note dead trees and browning of foliage on others. China©Juan Shi/Beijing Forestry University/Bugwood.org - CC BY-NC 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); the nematode is mycophagous and feeds on fungi in the wood, including bluestain fungi transmitted by engraver and other bark beetles. Japan.
TitleSecondary association
CaptionBursaphelenchus xylophilus (pine wilt nematode); the nematode is mycophagous and feeds on fungi in the wood, including bluestain fungi transmitted by engraver and other bark beetles. Japan.
Copyright©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US
Bursaphelenchus xylophilus (pine wilt nematode); the nematode is mycophagous and feeds on fungi in the wood, including bluestain fungi transmitted by engraver and other bark beetles. Japan.
Secondary associationBursaphelenchus xylophilus (pine wilt nematode); the nematode is mycophagous and feeds on fungi in the wood, including bluestain fungi transmitted by engraver and other bark beetles. Japan.©L.D. Dwinell/USDA Forest Service/Bugwood.org - CC BY 3.0 US

Identity

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Preferred Scientific Name

  • Bursaphelenchus xylophilus (Steiner & Buhrer, 1934) Nickle, 1970

Preferred Common Name

  • pine wilt nematode

Other Scientific Names

  • Aphelenchoides xylophilus Steiner & Buhrer, 1934
  • Bursaphelenchus lignicolus Mamiya & Kiyohara, 1972

International Common Names

  • English: pine wood nematode
  • French: nématode des pins; nématode du bois de pin

Local Common Names

  • Germany: Kiefernholznematode

EPPO code

  • BURSXY (Bursaphelenchus xylophilus)

Summary of Invasiveness

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B. xylophilus on its natural hosts behaves like other members of the genus, living a mycophagous life cycle on trees weakened or damaged by other causes. When introduced into new continents, it encounters new host species of Pinus, some of which are exceptionally susceptible, so that the nematode follows a 'phytophagous' life cyle. Readily transmitted by local Monochamus spp., it invades and destroys pine forests.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Nematoda
  •             Family: Parasitaphelenchidae
  •                 Genus: Bursaphelenchus
  •                     Species: Bursaphelenchus xylophilus

Notes on Taxonomy and Nomenclature

Top of page The species first came to widespread attention with the paper of Mamiya and Kiyohara (1972) which described Bursaphelenchus lignicolus as a new species from Japan. Subsequent research revealed that the species had been previously described from the USA as Aphelenchoides xylophilus by Steiner and Buhrer (1934), but had been subsequently overlooked. Later it was described again, as Bursaphelenchus lignicolus, when recognized to be the causal agent of pine wilt disease in Japan (Mamiya and Kiyohara, 1972). The synonymy was recognized in 1981 (Nickle et al., 1981). A very similar but non-pathogenic species (B. mucronatus) was described by Mamiya and Enda (1979), differing morphologically only in minor respects from B. xylophilus and most obviously by the presence in the female of a caudal mucron (finger-like projection) in the former species which was absent in the latter. However, populations of B. xylophilus were subsequently discovered in the USA which also carried a mucron on the tail. There has thus been much discussion about the taxonomic relationships between these two species, and also with B. fraudulentus Ruhm, a nematode from deciduous trees in Germany. Biochemical studies of several populations of these nematodes have clearly confirmed the distinctness of the three species (Webster et al., 1990; Abad et al., 1991). It is suggested that they constitute a species complex or supraspecies, separating from one another by reproductive isolation; B. xylophilus is a native of North America, whereas the other two are Palaearctic species, one colonizing coniferous trees, the other deciduous. B. xylophilus found in Japan and other Asian countries is obviously an introduction from North America. Another apparently closely related species, Bursaphelenchus kolymensis Korenchenko, has been described from Larix from the Far East of Russia (Korenchenko, 1980); this nematode has not been studied extensively, but is possibly synonymous with B. mucronatus.

Description

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Measurements (after Nickle et al., 1981)

Female lectotypes (n=5): L=0.52 (0.45-0.61) mm; a=42.6 (37-48); b=9.6 (8.3-10.5); c=27.2 (23-31); V=74.7 (73-78)%; stylet=12.8 (12.6-13.0) µm.

Male lectotypes (n=5): L=0.56 (0.52-0.60) mm; a=40.8 (35-45); b=9.4 (8.4-10.5); c=24.4 (21-29); stylet=13.3 (12.6-13.8) µm; spicule=21.2 (18.8-23.0) µm.

Measurements (after Mamiya and Kiyohara, 1972)

Female (n=40): L=0.81 (0.71-1.01) mm; a=40.0 (33-46); b=10.3 (9.4-12.8); c=26.0 (23-32); V=72.7 (67-78)%; stylet=15.9 (14-18) µm.

Male (n = 30): L=0.73 (0.59-0.82) mm; a=42.3 (36-47); b=9.4 (7.6-11.3); c=26.4 (21-31); stylet=14.9 (14-17) µm; spicules=27.0 (25-30) µm.

Description (after Nickle et al., 1981)

Female: cephalic region high, offset, with six lips. Stylet with small basal swellings. Oesophageal gland lobe slender and about 3-4 body-widths long. Excretory pore located at about the level of the oesophago-intestinal junction, occasionally at the same level as the nerve ring. Hemizonid about 0.67 of a body-width behind the median bulb. Vulva posterior, the anterior lip overhanging to form a flap. Genital tract monoprodelphic, outstretched. Developing oocytes mostly in single file. Post-uterine sac well developed, extending for 0.75 or more of the distance to the anus. Tail subcylindroid with a broadly rounded terminus. Mucron usually absent, but some populations may have a short, 1-2 µm, mucron.

Male: similar to female in general respects. Spicules large, strongly arcuate so that the prominent transverse bar is almost parallel to the body axis when the spicules are retracted. The apex is bluntly rounded and the rostrum prominent and pointed. The distal tip of each spicule is expanded into a disc-like structure named the cucullus. The tail is arcuate with a pointed, talon-like terminus bearing a small bursa. Seven caudal papillae are present; one pair adanal, a single preanal ventromedian papilla, and two postanal pairs near the tail spike and just anterior to the start of the bursa.

A morphological key to the species of the xylophilus group of the genus Bursaphelenchus has recently been published by Braasch and Schönfeld (2015).

Distribution

Top of page B. xylophilus is indigenous to North America, particularly the USA, and has probably been introduced elsewhere by infected timber/wood products. In Europe, the nematode has been detected in imported timber in Finland, Norway, Sweden and France.

It is presumed that B. xylophilus originated in North America and was transported from there to the southern Japanese island of Kyushu in infested timber at some time around the beginning of the twentieth century (Nickle et al., 1981; Mamiya, 1983; Malek and Appleby, 1984). The fact that native American conifers are mostly resistant, while Japanese species are susceptible, tends to support this view. From Japan, B. xylophilus has spread to other Asian countries (Li et al., 1983), but not to Russia (Kulinich and Kolosova, 1995; Kulinich and Orlinskii, 1998).

Surveys to determine whether B. xylophilus may be present have been conducted in several European countries, including Finland, Germany, Netherlands, Norway, Poland, Sweden and the UK, but the species was not found. Furthermore, an examination in Finland of 150 consignments of conifer wood from European countries failed to detect the species. B. xylophilus was reported on P. pinaster in south-west France (Baujard et al., 1979), but later microscopic and biochemical examination showed that the nematode involved was, in fact, B. mucronatus. It was found associated with dead or dying Pinus, but it was concluded that it was not responsible for the mortality. As well as in France, B. mucronatus has been found in Austria, Finland, Norway, Sweden and the USSR (see also De Guiran and Boulbria (1986)).

Species of Monochamus, the main vectors, are found throughout the northern hemisphere, and many have been recorded as having species of Bursaphelenchus as associates; it is assumed, therefore, that most, if not all, Monochamus species would be capable of transmission to a greater or lesser extent. However, the only species known to transmit B. xylophilus and likely to carry the nematode on importation are those from North America and eastern Asia. Of the species recorded as carrying B. xylophilus, M. alternatus occurs in Japan, China, Taiwan, Laos and the Republic of Korea, M. nitens and M. saltuarius in Japan, Siberia and northern China, and the others in Canada and the USA.

See also CABI/EPPO (1999, No. 789).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ChinaPresentIntroduced1982 Invasive EPPO, 2014; CABI/EPPO, 2015
-AnhuiPresent1988EPPO, 2014; CABI/EPPO, 2015
-ChongqingPresentEPPO, 2014; CABI/EPPO, 2015
-FujianPresentEPPO, 2014; CABI/EPPO, 2015
-GansuPresentCABI/EPPO, 2015
-GuangdongPresent1988EPPO, 2014; CABI/EPPO, 2015
-GuangxiPresentEPPO, 2014; CABI/EPPO, 2015
-GuizhouPresentEPPO, 2014; CABI/EPPO, 2015
-Hong KongPresentEPPO, 2014; CABI/EPPO, 2015
-HubeiPresentEPPO, 2014; CABI/EPPO, 2015
-HunanPresentEPPO, 2014; CABI/EPPO, 2015
-JiangsuPresent1982Zhang and Huang, 1990; EPPO, 2014; CABI/EPPO, 2015
-JiangxiPresentEPPO, 2014; CABI/EPPO, 2015
-LiaoningPresentCABI/EPPO, 2015
-ShaanxiPresentEPPO, 2014; CABI/EPPO, 2015
-ShandongPresent1991Wu et al., 2013; EPPO, 2014; CABI/EPPO, 2015
-ShanghaiPresentWang et al., 2004
-SichuanPresentEPPO, 2014; CABI/EPPO, 2015
-YunnanPresentCABI/EPPO, 2015
-ZhejiangPresent1991EPPO, 2014; CABI/EPPO, 2015
JapanPresentIntroduced Invasive EPPO, 2014; CABI/EPPO, 2015
-HonshuPresentEPPO, 2014
-KyushuPresentEPPO, 2014
-Ryukyu ArchipelagoPresentEPPO, 2014
-ShikokuPresentEPPO, 2014
Korea, Republic ofPresentIntroduced Invasive EPPO, 2014; CABI/EPPO, 2015
TaiwanWidespreadIntroducedEPPO, 2014; CABI/EPPO, 2015

Africa

NigeriaAbsent, unreliable recordIntroducedKhan and Gbadegesin, 1991; EPPO, 2014; CABI/EPPO, 2015
South AfricaPresent, few occurrencesIntroduced Not invasive Braasch et al., 1998

North America

CanadaWidespreadNative Not invasive EPPO, 2014; CABI/EPPO, 2015
-AlbertaPresentEPPO, 2014; CABI/EPPO, 2015
-British ColumbiaPresentEPPO, 2014; CABI/EPPO, 2015
-ManitobaPresentEPPO, 2014; CABI/EPPO, 2015
-New BrunswickPresentEPPO, 2014; CABI/EPPO, 2015
-Newfoundland and LabradorPresentBowers et al., 1992; EPPO, 2014; CABI/EPPO, 2015
-Northwest TerritoriesPresentBowers et al., 1992; EPPO, 2014; CABI/EPPO, 2015
-Nova ScotiaPresentBowers et al., 1992; EPPO, 2014; CABI/EPPO, 2015
-NunavutPresentCABI/EPPO, 2015
-OntarioPresentEPPO, 2014; CABI/EPPO, 2015
-QuebecPresentEPPO, 2014; CABI/EPPO, 2015
-SaskatchewanPresentEPPO, 2014; CABI/EPPO, 2015
-Yukon TerritoryPresentBowers et al., 1992; EPPO, 2014; CABI/EPPO, 2015
MexicoPresentNative1993 Not invasive EPPO, 2014; CABI/EPPO, 2015
USAWidespreadNative Not invasive EPPO, 2014; CABI/EPPO, 2015
-AlabamaPresentEPPO, 2014; CABI/EPPO, 2015
-ArizonaPresentCABI/EPPO, 2015
-ArkansasPresentEPPO, 2014; CABI/EPPO, 2015
-CaliforniaPresentEPPO, 2014; CABI/EPPO, 2015
-ColoradoPresentBlunt et al., 2014; EPPO, 2014; CABI/EPPO, 2015
-ConnecticutPresentEPPO, 2014; CABI/EPPO, 2015
-DelawarePresentEPPO, 2014; CABI/EPPO, 2015
-FloridaPresentEPPO, 2014; CABI/EPPO, 2015
-GeorgiaPresentEPPO, 2014; CABI/EPPO, 2015
-IllinoisPresentEPPO, 2014; CABI/EPPO, 2015
-IndianaPresentEPPO, 2014; CABI/EPPO, 2015
-IowaPresentEPPO, 2014; CABI/EPPO, 2015
-KansasPresentEPPO, 2014; CABI/EPPO, 2015
-KentuckyPresentEPPO, 2014; CABI/EPPO, 2015
-LouisianaPresentEPPO, 2014; CABI/EPPO, 2015
-MarylandPresentEPPO, 2014; CABI/EPPO, 2015
-MassachusettsPresentEPPO, 2014; CABI/EPPO, 2015
-MichiganPresentEPPO, 2014; CABI/EPPO, 2015
-MinnesotaPresentEPPO, 2014; CABI/EPPO, 2015
-MississippiPresentEPPO, 2014; CABI/EPPO, 2015
-MissouriPresentEPPO, 2014; CABI/EPPO, 2015
-NebraskaPresentEPPO, 2014; CABI/EPPO, 2015
-New JerseyPresentEPPO, 2014; CABI/EPPO, 2015
-New YorkPresentEPPO, 2014; CABI/EPPO, 2015
-North CarolinaPresentEPPO, 2014; CABI/EPPO, 2015
-OhioPresentEPPO, 2014; CABI/EPPO, 2015
-OklahomaPresentEPPO, 2014; CABI/EPPO, 2015
-OregonPresent1996EPPO, 2014; CABI/EPPO, 2015
-PennsylvaniaPresentEPPO, 2014; CABI/EPPO, 2015
-South CarolinaPresentEPPO, 2014; CABI/EPPO, 2015
-TennesseePresentEPPO, 2014; CABI/EPPO, 2015
-TexasPresentEPPO, 2014; CABI/EPPO, 2015
-VermontPresentEPPO, 2014; CABI/EPPO, 2015
-VirginiaPresentEPPO, 2014; CABI/EPPO, 2015
-West VirginiaPresentEPPO, 2014; CABI/EPPO, 2015
-WisconsinPresentEPPO, 2014; CABI/EPPO, 2015

Europe

DenmarkAbsent, confirmed by surveyEPPO, 2014
EstoniaAbsent, confirmed by surveyEPPO, 2014
FinlandAbsent, intercepted onlyIntroducedEPPO, 2014
FranceAbsent, intercepted onlyEPPO, 2014
ItalyAbsent, confirmed by surveyEPPO, 2014
LatviaAbsent, confirmed by surveyEPPO, 2014
LithuaniaAbsent, confirmed by surveyEPPO, 2014
MaltaAbsent, confirmed by surveyEPPO, 2014
NetherlandsAbsent, confirmed by surveyEPPO, 2014
NorwayAbsent, intercepted onlyIntroducedEPPO, 2014
PolandAbsent, confirmed by surveyEPPO, 2014
PortugalRestricted distributionIntroduced Not invasive Mota et al., 1999; EPPO, 2011; EPPO, 2014; CABI/EPPO, 2015; Inácio et al., 2015
-MadeiraRestricted distributionEPPO, 2014; CABI/EPPO, 2015
-Portugal (mainland)Restricted distributionCABI/EPPO, 2015
SlovakiaAbsent, confirmed by surveyEPPO, 2014
SloveniaAbsent, confirmed by surveyEPPO, 2014
SpainTransient: actionable, under eradicationAbelleira et al., 2011; CABI/EPPO, 2015; Zamora et al., 2015; EPPO, 2018
SwedenAbsent, intercepted onlyIntroducedEPPO, 2014
UKAbsent, confirmed by surveyEPPO, 2014

Risk of Introduction

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B. xylophilus and its vectors, Monochamus species, are regulated by the European Union (EU, 2000) and by other EPPO countries, on the basis of a detailed Pest Risk Analysis (Evans et al., 1996). It is also treated as a quarantine pest in Asia (particularly China), in South America and in Oceania (Mireku and Simpson, 2002; Ridley et al., 2000). Infested wood is the most probable means of international transport of B. xylophilus, and the species has been detected on a number of occasions in sawn wood, round wood and wood chips imported into Europe from the USA and Canada. The introduction of the nematodes within wood imports does not, in itself, represent a threat to the forests of the EPPO region (Magnusson, 1986). It is necessary for a pathway to be found for the nematode to come into contact with a native vector, and this can probably only be achieved if the nematode first invades wood which contains juveniles or pupae of a potential vector. Several species of Monochamus are present in Europe and have been shown to transmit the closely related B. mucronatus (Tomminen, 1990). Nematodes can move very actively from wood chips or sawdust, and the connection with the vector could be made if such material were to come into contact with tree stumps or cut logs (Skwiercz, 1988). Within the wood processing industry, the same means of transport is sometimes used for collecting both imported and local wood material (McNamara and Støen, 1988).

B. xylophilus is more likely to be introduced by any given pathway if it is imported together with vector insects. Such insects can only survive if the wood has a sufficient moisture content, greater than that needed by the nematode. The larger the pieces of timber, the longer insects are liable to survive, and therefore round wood and sawn wood present a greater risk than wood chips. Wood chips can have a high moisture content, allowing ready nematode survival, but the processing undergone in their preparation reduces the possibility of vectors surviving (Kinn, 1986).

Soliman (2012) predicted significant impacts caused by B. xylophilus in Europe in Portugal, Spain, southern Franec and northwest Italy.

Hosts/Species Affected

Top of page Most species of Pinus can act as hosts, but the following are especially susceptible to damage: the Asiatic Pinus thunbergii, Pinus densiflora, Pinus luchuensis, the European Pinus nigra, Pinus pinaster, Pinus sylvestris, the American Pinus radiata, Pinus lambertiana and Pinus echinata. Pine wilt disease is limited primarily to exotic, often stressed, pines such as Scots (P. sylvestris), Austrian (P. nigra), Japanese red (P. densiflora) and Japanese black (P. thunbergii) pines.

Other conifers can also act as hosts, but reports of damage are rare. Isolated cases of death of Picea and Pseudotsuga due to this nematode have been reported in the USA (Malek and Appleby, 1984). The expanded host list is based on Evans et al. (1996).

The nematode lives within the resin canals and sapwood of the host and is also closely associated with a variety of wood-boring beetles that vector the nematode.

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Abies amabilis (Pacific silver fir)PinaceaeOther
Abies balsamea (balsam fir)PinaceaeOther
Abies firma (momi fir)PinaceaeOther
Abies grandis (grand fir)PinaceaeOther
Abies sachalinensis (Sakhalin fir)PinaceaeOther
Cedrus atlantica (Atlas cedar)PinaceaeOther
Cedrus deodara (Himalayan cedar)PinaceaeOther
Larix decidua (common larch)PinaceaeOther
Larix kaempferi (Japanese larch)PinaceaeOther
Larix laricina (American larch)PinaceaeOther
Larix occidentalis (western larch)PinaceaeOther
Picea abies (common spruce)PinaceaeOther
Picea engelmannii (Engelmann spruce)PinaceaeOther
Picea glauca (white spruce)PinaceaeOther
Picea jezoensis (Yeddo spruce)PinaceaeOther
Picea mariana (black spruce)PinaceaeOther
Picea pungens (blue spruce)PinaceaeOther
Picea rubens (red spruce)PinaceaeOther
Picea sitchensis (Sitka spruce)PinaceaeOther
Pinus (pines)PinaceaeMain
Pinus ayacahuite (Mexican white pine)PinaceaeOther
Pinus banksiana (jack pine)PinaceaeMain
Pinus brutia (brutian pine)PinaceaeOther
Pinus bungeana (lace bark pine)PinaceaeOther
Pinus caribaea (Caribbean pine)PinaceaeOther
Pinus contorta (lodgepole pine)PinaceaeOther
Pinus densiflora (Japanese umbrella pine)PinaceaeMain
Pinus echinata (shortleaf pine)PinaceaeMain
Pinus elliottii (slash pine)PinaceaeMain
Pinus halepensis (Aleppo pine)PinaceaeOther
Pinus hartwegii (Hartweg pine)PinaceaeOther
Pinus jeffreyi (Jeffrey pine)PinaceaeOther
Pinus koraiensis (fruit pine)PinaceaeOther
Pinus lambertiana (big pine)PinaceaeMain
Pinus leiophylla (smooth-leaved pine)PinaceaeOther
Pinus luchuensis (luchu pine)PinaceaeMain
Pinus massoniana (masson pine)PinaceaeOther
Pinus monticola (western white pine)PinaceaeOther
Pinus mugo (mountain pine)PinaceaeOther
Pinus nigra (black pine)PinaceaeMain
Pinus oocarpa (ocote pine)PinaceaeOther
Pinus palustris (longleaf pine)PinaceaeOther
Pinus pinaster (maritime pine)PinaceaeOther
Pinus pinea (stone pine)PinaceaeOther
Pinus ponderosa (ponderosa pine)PinaceaeOther
Pinus pungens (tabel Mountain pine)PinaceaeOther
Pinus radiata (radiata pine)PinaceaeMain
Pinus resinosa (red pine)PinaceaeMain
Pinus strobiformis (southwestern white pine)PinaceaeOther
Pinus strobus (eastern white pine)PinaceaeMain
Pinus sylvestris (Scots pine)PinaceaeMain
Pinus taeda (loblolly pine)PinaceaeMain
Pinus thunbergii (Japanese black pine)PinaceaeMain
Pinus wallichiana (blue pine)PinaceaeOther
Pinus yunnanensis (Yunnan pine)PinaceaeOther
Pseudotsuga menziesii (Douglas-fir)PinaceaeOther
Xanthocyparis nootkatensis (Alaska cedar)Other

Growth Stages

Top of page Vegetative growing stage

Symptoms

Top of page The first indication of the presence of nematodes in the tree is a reduction of oleoresin production in reaction to wounding. Transpiration from the leaves decreases and later stops completely. The first obvious external symptom is the yellowing and wilting of the needles, leading to eventual death of the tree (Mamiya, 1983). The wilting may first appear on only one branch ('flag'), although the whole tree may later show symptoms (Malek and Appleby, 1984).

List of Symptoms/Signs

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SignLife StagesType
Leaves / wilting
Leaves / yellowed or dead
Whole plant / plant dead; dieback

Biology and Ecology

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B. xylophilus is known to have two different types of life cycle, mycophagous and phytophagous (Wingfield, 1983). In both cases the nematodes are transmitted from one host to the next by species of Monochamus. In the mycophagous life cycle, fourth-stage juveniles of the nematodes are transmitted to recently dead or dying trees during oviposition by the female vector. The nematodes leave the beetle and enter the tree through the hole in the bark cut by the vector to lay its eggs. Within the wood the nematodes feed on the hyphae of fungi (usually Ceratocystis species) also transmitted to the wood by ovipositing beetles. Immediately on entering the wood the larval nematodes moult to adult and begin laying eggs. The population is composed of males, females and four juvenile stages in this propagative stage of rapid multiplication.

At a certain time after the initial invasion by the nematodes, the population ceases to multiply and begins to decline. A different type of third-stage juvenile is produced; this is called the 'dispersal third-stage juvenile' (Mamiya, 1983), although it is more correctly a survival stage, being capable of resisting adverse conditions. It is likely that the population structure of the nematodes changes in reaction to a reduction in the availability of food, when the fungus has fully exploited the wood. The 'dispersal' juveniles gather in the wood surrounding the pupal chamber of the Monochamus vector, possibly under the influence of substances diffusing from the developing pupa. Close to the time of emergence of the beetle, the nematodes moult into the special fourth-stage juveniles, called the 'dauerlarvae'. Fungal hyphae also develop around the pupation chambers. The fungus forms long-necked perithecia projecting into the chamber, and the nematodes gather at the tips of the perithecia. When the young adult beetle emerges, it brushes against the perithecial necks, picking up the nematodes which settle below the elytra and, in particular, in the tracheae. The immature adult beetle then flies from the wood carrying nematodes.

This mycophagous life cycle can be considered to be the normal life cycle of B. xylophilus and is similar to that of most other species of Bursaphelenchus. that have phoretic relationships with forest beetles. In North America, it is presumably the most common condition (Wingfield, 1983). However, in Asia, and also in North America wherever the nematode comes into contact with non-native or susceptible species of Pinus, the phytophagous life cycle predominates. In this latter cycle, the nematodes are transmitted from young adult beetles shortly after emergence from their pupal chambers, when they fly to feed on young Pinus shoots. The nematodes enter the shoots through the feeding wounds. This form of transmission only occurs on susceptible species of Pinus presumably because Pinus species native to the area where B. xylophilus occurs develop physical or biochemical barriers to prevent direct invasion to healthy tissues.

In the young Pinus shoots, B. xylophilus multiplies in the resin canals, attacking their epithelial cells. About 3 weeks later, the tree shows first symptoms of 'drying out', in the form of reduced oleoresin exudation. The nematodes can now move freely throughout the dying tree which becomes attractive to adult insects which gather on the trunks to mate. At this stage, intensified wilting and yellowing of the needles is seen. The tree dies 30-40 days after infection, and may then contain millions of nematodes throughout the trunk, branches and roots. The remainder of the phytophagous life cycle is similar to the mycophagous, as the nematodes locate the pupa of Monochamus just before emergence.

In the laboratory, B. xylophilus can be maintained on fungal cultures. It reproduces in 12 days at 15°C, 6 days at 20°C and 3 days at 30°C. Laying starts on the fourth day after hatching, and the eggs hatch in 26-32 h at 25°C. The temperature threshold for development is 9.5°C.

Species of Monochamus are the principal vectors of B. xylophilus, and of these M. alternatus is the major vector in Japan, whereas M. carolinensis is the major vector in North America. Other less efficient vectors quoted in the literature are, in Japan, M. nitens and M. saltuarius, and in North America, M. marmorator, M. mutator [M. clamator], M. obtusus, M. scutellatus and M. titillator. In Portugal, where there is a recent outbreak of B. xylophilus, the European Monochamus galloprovincialis has been shown the carry the pest when it emerges from infested trees of Pinus pinaster (but transmission has not been demonstrated (Sousa et al., 2001)).

The propagative form of the pine wilt nematode B. xylophilus develops and reproduces in both susceptible healthy and dying pines (Mamiya, 1984). Monochamus beetles are the main vectors of the nematode and are attracted to dying trees where the beetles locate mates and copulate. Females deposit eggs underneath the bark, and the nematodes exit the beetle's trachea and enter the wood through the oviposition wounds. M. carolinensis matures in dead pine, and B. xylophilus enters the beetles following the beetles' moult from pupae to adults and just prior to the beetles' emergence from the trees. A specialized life stage of the nematode, the JIV dispersal juvenile, is the nematode stage that is vectored. B. xylophilus are then carried to healthy trees, where they enter through beetle feeding wounds.

M. alternatus, M. carolinensis and M. saltuarius have stronger flying and dispersal ability than other Monochamus beetles so control and management of pine wilt disease focuses on these three primary vector insects. Most adults of these insects can reach up to 1000 m in one flight, both in the maturation feeding and oviposition stages (Zhang, etal., 2007). 

Other genera of the Cerambycidae (for example, Acalolepta, Acanthocinus, Amniscus, Arhopalus, Asemum, Corymbia, Neacanthocinus, Rhagium, Spondylis, Uraecha, Xylotrechus) and other Coleoptera (for example, Chrysobothris, Hylobius, Pissodes) have been found to carry nematodes in or on their bodies, but there is no evidence that they have any role as vectors.

Lai et al. (2002) suggest that attacks by defoliating pests (Dendrolimus punctatus) may predispose pines to infection by B. xylophilus.

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Rhizopogon rubescens Pathogen Japan
Suillus luteus Pathogen Japan

Means of Movement and Dispersal

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Species of Monochamus are the principal vectors of B. xylophilus, and of these M. alternatus is the major vector in Japan, whereas M. carolinensis is the major vector in North America. Other less efficient vectors quoted in the literature are, in Japan, M. nitens and M. saltuarius, and in North America, M. marmorator, M. mutator [M. clamator], M. obtusus, M. scutellatus and M. titillator. In Portugal, where there is a recent outbreak of B. xylophilus, the European Monochamus galloprovincialis has been shown the carry the pest when it emerges from infested trees of Pinus pinaster (but transmission has not been demonstrated (Sousa et al., 2001)).

 

Seedborne Aspects

Top of page The nematode is not seedborne.

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Containers and packaging - woodPinewood Yes
Land vehicles Yes
Soil, sand and gravel Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Bulbs/Tubers/Corms/Rhizomes adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Flowers/Inflorescences/Cones/Calyx adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Growing medium accompanying plants adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Leaves adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Seedlings/Micropropagated plants adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Stems (above ground)/Shoots/Trunks/Branches adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Wood adults; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Plant parts not known to carry the pest in trade/transport
Fruits (inc. pods)
Roots
True seeds (inc. grain)

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production None
Environment (generally) Negative
Fisheries / aquaculture None
Forestry production Negative
Human health None
Livestock production None
Native fauna None
Native flora Negative
Rare/protected species Negative
Tourism None
Trade/international relations Negative
Transport/travel None

Impact

Top of page Pine wilt disease was first reported in Japan in 1913 in the Nagasaki region, but the causal agent was only identified as B. xylophilus in 1972 (Mamiya and Kiyohara, 1972). The symptoms were first attributed to wood-boring insects, which are found abundantly on infected trees, but it was then found that first symptoms precede attack by the insects. The disease then began to spread northwards causing very severe losses throughout the country. Over 1,000,000 m³ of wood were being lost per year at the end of the 1940s, but a campaign for destroying infected trees then brought this figure below 500,000 m³ per year (still a substantial loss). However, because industrialization has reduced the availability of manpower for the forests, and because wood has been replaced by oil as a fuel, infected trees are again remaining standing as reservoirs of the nematode. In consequence, the loss curve turned sharply upwards from 1970 and now even exceeds 2,000,000 m³ per year. Almost all the Japanese archipelago is affected, from the Ryukyu Islands in the far south, where P. luchuensis is very susceptible, to the northern part of the island of Honshu, with much colder climates where the mean annual temperature is 10-12°C. It seems probable that this northward spread is due to heavy population pressure from the south. Only the most northern island of Hokkaido is still not affected.

In 1979, B. xylophilus was associated with the death of Pinus in Missouri, USA, primarily of P. sylvestris growing in amenity plantings (Malek and Appleby, 1984), and in the USA in general losses arise almost exclusively among exotic species and in artificial forest ecosystems such as ornamental conifer plantings, wind-breaks and Christmas tree plantations. B. xylophilus is widespread in natural coniferous forests, but significant losses have not been recorded.

Economic Impact

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Soliman (2012), modelling an unregulated infestation of B. xylphilus in the EU, estimated that the loss of forestry stock over 22 years (2008-2030) would cost 22 billion euros.

Environmental Impact

Top of page B. xylophilus is a highly invasive species, colonizing and damaging natural or managed pine forests in areas outside its natural range. In Japan, forests of Pinus densiflora and Pinus thunbergii severely affected by B. xylophilus tend to be succeeded by deciduous oak forest (Quercus serrata) in central Japan, and evergreen oak forest (Quercus glauca) further south (Fujihara et al., 1992; Fujihara, 1996). Pine forest only persists on upper slopes, where damage is less severe (Fujihara et al., 1999). Species diversity is initially reduced, but progressively recovers as the oak forest establishes (Katagiri et al., 1995). In the southern island of Kyushu (Inoue, 1995), pine is replaced by more tropical evergreen trees (Mallotus japonicus and Rhus succedanea). Similarly, in Taiwan (Ma et al., 2002), Pinus luchuensis is replaced by the evergreen Mallotus paniculatus.

Impact: Biodiversity

Top of page B. xylophilus presents a direct threat to the survival of the very local endemic Pinus armandii var. Amamiana in southern Japan (Kanetani et al., 1999).

Social Impact

Top of page Destruction of pine forests in Japan initially affected local employment, but this was overtaken by post-war economic development involving a much diminished reliance of local populations on forest products. In fact, this decline in forest use has aggravated losses due to B. xylophilus, as damaged forests tended to be neglected.

Detection and Inspection

Top of page Before any symptoms appear in trees suspected of being infested, the reduction of oleoresin production can be detected by making a hole of 10-15 mm diameter through the bark and cambium (Oda, 1967). Nematodes can be extracted from trees showing symptoms by taking trunk cores and then soaking the cores in water for several days; the nematodes will emerge from the wood into the water.

EPPO's recommendations to prevent the introduction of B. xylophilus and its vectors cover plants and wood of all conifers, apart from Thuja plicata, from countries where the nematode occurs. It is recommended that coniferous plants for planting should be prohibited. Wood (including chips) may be prohibited, but can alternatively be treated (heat treated to a core temperature of 56°C for 30 minutes, or fumigated) (Soma et al., 2003) in the case of chips. In the case of wood packing, ISPM no. 15 can be applied (IPPC, 2002).

Other phytosanitary treatments for wood chips have been proposed, such as steam/heat treatment or fumigation in transit with phosphine (Kinn, 1986). Such treatment can be expensive in relation to the value of the commodity.

EPPO also recommends measures to be taken within a country if an outbreak of B. xylophilus is found (OEPP/EPPO, 2003).

The main risk of infection of cut timber is in the period between felling and removal from the forest. Cut logs can be protected from oviposition (and thus from introduction of nematodes) by chemical treatment, but such treatment is more effective in killing the insect larvae already present under the bark; in the latter case, the treatment is too late to prevent nematode infection. Other means of reducing the risk of attack are to cover logs after felling, to leave trap logs exposed nearby and to ensure that the felling is conducted outside the flight period of the beetles (Raske, 1973; Dominik, 1981).

The only known effective treatment for wood already infected with B. xylophilus and its vectors appears to be heat treatment, in which all parts of the wood reach a temperature of 56°C for at least 30 minutes; commercial kiln practices normally achieve this. Inspection of timber does not always reveal the presence of insect larvae or pupae, which can be hidden within internal galleries.

Similarities to Other Species/Conditions

Top of page B. xylophilus is superficially similar to other species of the genus, although these are not regarded a pests. It can be distinguished from most of these by the unusual shape of the male spicules and the presence of a vulval flap in the female. However, there is a group of Bursaphelenchus species sharing these characters and differentiating B. xylophilus from these species requires considerable expertise (see the EPPO Diagnostic Protocol for B. xylophilus; OEPP/EPPO, 2001). Techniques based on PCR methodologies are currently being developed to facilitate unequivocal identification (see, for example, Braasch et al., 1995; Irdani et al., 1995a, b). There is also a species of Laimaphelenchus recorded from North America and Europe that may be confused with B. xylophilus - the spicule form is similar and the female also has a vulval flap.

Prevention and Control

Top of page So far it has proved impossible to control nematodes once introduced into a tree. Therefore, control of pine wilt disease in Japan has concentrated on a combination of cultural practices, in removing dead or dying trees from the forest to prevent their use as a source of further infection, and the control of the vector beetles by insecticidal treatment. The Japanese government has spent large amounts of money on extensive control programmes involving aerial spraying and removal of diseased trees (Ikeda, 1984). In the case of individual trees with a particular significance (for example, religious), infection can be prevented by a prophylactic chemical treatment. Research is continuing to try to find alternative means of control, such as biological control agents for both nematodes and vectors, insect attractants, breeding of resistant Pinus clones, and inducing resistance by inoculation of non-pathogenic strains of B. xylophilus. Muramoto (1999) reports that B. xylophilus has been successfully eradicated from Okinoeragu Island (in the Ryukyu Archipelago, Japan).

References

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