Bursaphelenchus xylophilus		Contents		Rev 09/06/2023
Pine wood nematode		Classification		Hosts
		Morphology and Anatomy		Life Cycle
Return to Bursaphelenchus Menu		Economic Importance		Damage
		Distribution		Management
Return to Aphelenchoididae Menu		Feeding		References
		Go to Nemaplex Main Menu		Go to Dictionary of Terminology

Classification:

Chromadorea
Rhabditida
Tylenchina
Aphelenchoidea
Aphelenchoididae

Bursaphelenchinae

     Bursaphelenchinae

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

Synonym:
Bursaphelenchus lignicolus

Originally described as Aphelenchoides xylophilus by Steiner and Buhrer in 1934 from blue-stained logs of Pinus palustris at a sawmill in Bogalusa, Louisiana.

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Morphology and Anatomy:

	Female: Genus is characterized by vulval flap; the post-uterine sac is long.       Male: Shape of spicules and caudal alae at tail tip are characteristic of genus.  The male tail is curved ventrally, conoid and has a pointed terminus.  The spicules are well developed, with a prominent rostrum and are flattened into a disc-like cucullus  at the distal end. .
B. xylophilus has the general characteristics of Bursaphelenchus spp.: lips high and offset; weak stylet with small knobs; median bulb well developed; dorsal esophageal gland opening inside the median bulb. B. xylophilus can be distinguished by the simultaneous presence of three characters: The spicules are flattened into a disc-like structure (the cucullus) at the distal end.  The anterior vulval lip is a distinct overlapping flap and the posterior end of the female body is rounded in nearly all individuals ( this character separates B. xylophilus from B. mucronatus, a non-pathogenic species in which the female has a mucronate tail). However, it is difficult to differentiate between B. mucronatus and populations of B. xylophilus in North America that have mucronate tails.  (EPPO Bulletin).    Reported median body size for this species (Length mm; width micrometers; weight micrograms) - Click:

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Distribution:

Bursaphelenchus xylophilus was first described in, and is perhaps native to, North America.  The nematode occurs in 36 states in the U.S., including all the Great Plains states with the exception of North Dakota; almost all prefectures in Japan, several provinces in China. It also occurs in Canada, Mexico, Taiwan, Korea, and Portugal.

This and related species are vectored by cerambycid longhorn beetles, also known as sawyers, of the genus Monochamus. Several species of Bursaphelenchus have a phoretic relationship with Monochamus spp., which carry them to recently felled logs and dead or dying conifers, particularly pines. Monochamus, Bursaphelenchus, or both may be found in pine chips, unseasoned lumber, and logs. Consequently, it is easily transported in wood products, such as logs, lumber, pallets, crates, wood chips, and furniture, that are not kiln-dried.

The beetles are wood borers in the larval stage (Linit,1987). M. alternatus is the primary vector in Japan and China, but there are others. Monochamus galloprovincialis is considered an important vector in Europe (Abelleira et al., 2020)

When  introduced into Japan and other Asian countries, B. xylophilus became a destructive pest of pines.  Countries in the European Union and elsewhere regulate the import of all coniferous chips, sawn wood, and logs (Dwinell, 1997). 

The nematode can also be vectored by the pine sawyer beetle to a dying tree or freshly cut timber during the female beetle's oviposition or egg-laying. This is the more likely transmission pathway in North America, where the pinewood nematode is thought to be native. The nematode can also feed on fungi growing in dying or dead trees or in cut timber and thus can be

Monochamus spp. (Cerambycidae) sawyer beetles
Male	Adults:  Family characteristics of antennae, eyes and tarsi + generic characteristics of elongate cylindroidal form, prothorax with small conical projections from side, antennae very long, second segment very small. Female
	Larvae:  Elongate slightly tapered grub with thoracic plate above but none below, elliptical in cross-section, legs absent.
Damage by Sawyer Beetles: Grubholes elliptical, frass-filled, adult exit holes circular. Initial stage of attack shows as irregular channeling of wood surface. Larvae may tunnel more than one year before pupation. Principal Hosts of Sawyer Beetles: Species of Pinus, Picea, Abies and Douglas-fir.	Economic Importance of Sawyer Beetles: Larval boring causes extensive damage to dying, recently dead and felled conifers. In China and Japan, M. alternatus is the vector for pinewood nematode.

Pine wilt symptoms and insect damage (excerpt from Pine Wilt in Japan - Ministry of Agriculture, Forestry and Fisheries, Japan)

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Economic Importance:

C-rated pest in California Nematode Pest Rating System.

The causal agent ov Pine Wilt Disease which has been devastating to forests in East Asia and in some areas of Western Europe.

The annual loss of pine timber in Japan was 2.4 million cubic meters by the 1970s.

The nematode is reported from 36 states in the U.S. but may cause little direct damage. It has major economic consequences in that Scandinavian and other countries have established embargoes on wood and wood chips (e.g. for paper pulp) from inmfested areas and when nematodes are detecte4d during phytosanitary inspection. Samples from shipments suggest population increases in wood chips during voyage.

Economic analysis of Bursaphelenchus xylophilus as an invasive species in Europe (Soliman et al., 2012):

•  Economic impact assessment of an invasive species to the European forest industry requires integration of information on pest entry, establishment and spread, valuation of assets at risk and market consequences at large spatial scales. In this analysis, direct economic impacts resulting from wood loss were computed at both regional and continental scales.
• Substantial economic impacts are predicted for Portugal, Spain, Southern France, and North West Italy but not elsewhere in the European Union in the near future.
• The cumulative value of lost forestry stock in Europe over a period of 22 years (2008–2030), assuming no regulatory control measures, is estimated at 22 billion euros.
• The greatest annual loss of stock is expected to occur during 2014–2019, with a peak of three billion euros in 2016 and then stabilizing at 300–800 million euros/year.
• There is a time lag between the loss of forestry stock and reduction in social welfare.  Reduction in social welfare for the downstream round wood market is estimated at 218 million euros in 2030.  Consumers are predicted to experience a welfare loss of 357 million euros, while producers experience a 139 million euros increase in returns due to higher wood prices.
• The societal impact is expected to extend to well beyond the 2008-2030 time horizon of the analysis, and long after the invasion has stopped.
• In conclusin, Pinewood nematode has large economic consequences for the conifer forestry industry in the European Union.

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Feeding:

Nematodes spread through axial and radial resin canals of pine trees, feeding on epithelial cells.

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Hosts:

Pine.

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Life Cycle:

Ecophysiological Parameters:

Sexually reproducing. Insect vectors include several beetles, especially Cerambycidae.

Detailed studies on the mating behavior of B. xyopihilus (Liu et al., 2014) documented a series of sub-behaviors in the mating process:

Phase	Sub-behavior	Characteristic
Searching (+/- 22 min.)	Cruising	Female and male swim actively in a new environment
	Approaching	Female and male swim directly towards each other
	Encountering	Female and male approach closely, encounter and make head contact
Contacting (+/- 28 min.)	Touching	Female and male touch each other with the head, expecially in genital regions
	Hooping	Mail curves tail into 1-3 loops around female body
	Locating	Male slides along female body until spicules are above vulva; female moves in body-swinging motion
Copulating (+/- 24 min.)	Attaching	Male tightens loops and clamps to vulval region(photograph from Liu et al., 2014)
	Ejaculating	Male inserts spicules into vulva and ejaculates sperm
	Separating	Male loosens coiled tail and slides from female body
Lingering (+/- 7 min.)	Quiescences	Male and female appear transiently quiescent
		Male moves and roams, touches female occasionally; female remains without vigorous movement

The probability of male:female contacts ot female:J4 within 1 hour was 100%, 90% for male:j4  but only 30% for female:female contact, 70% for male:male contact.  Male head movement frequency increase significantly when introduced into water previously occupied by a female, indicating that females produce sex-attractant pheromones.

Dauer larvae are carried most frequently by Pine Sawyer beetles (M. alternatus) in Japan and by related species in the U.S.

In a damaged pine forest in Japan, >75% of Pine Sawyer adults had dauer larvae, averaging 15,000/insect, with a maximum of 230,000.

Insect lays eggs in bark of weakened tree; larvae hatch after 1 week; larvae burrow into wood and molt, creating a U-shaped tunnel back toward surface ending in pupal chamber.

Adult becomes infested with nematodes as it emerges from pupa and burrows to the surface.
	Nematodes usually remain on the surface and in tracheae of beetles. The insect then flies to a healthy tree and feeds on young tissues; nematodes infect the tree.

Phoretic relationship of insect and nematode (excerpt from Pine Wilt in Japan - Ministry of Agriculture, Forestry and Fisheries, Japan)

In the early stages of an infection the nematodes disperse through resin canals in the tree cortex and xylem of Pinus species; they multiply in the inner bark and xylem tissues.

Nematode development requires 5 days to adult, followed by 28 days of oviposition of 80 eggs per day. With unlimited resources a single female could give rise to 260,000 offspring in 15 days.

Ther resting stage of nematode, the 4th stage dauer larva, appears at high population densities. The dauer larva survives dry conditions, lack of food, cold, etc. - thicker cuticle, denser body contents. It is also the dispersal stage. The dauer larvae enter the pupae of the insect through spiracles and up to 100,000 are carried in the tracheae.

(Life cycle diagram from University of Vermont)

Bursaphelenchus xylophilus is readily cultured in lab on Botrytis cinerea and other fungi.

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Damage:

Pine tree death, Kansas

Trees already infected decline, thus attracting more insects to weakened trees for oviposition. A new generation of insects then becomes infected in the diseased trees. Drought and other stress may hasten the decline of trees. Damage due to pine wilt nematode has often been attributed to fungi, insects, etc.

Nematodes can be present in dead or living wood, and Wingfield points out that presence does not indicate that it killed the tree as it is primarily a fungus feeder. However, direct inoculation of the nematode into trees in Japan killed 100% of the trees.

Tree death occurs within in 1 year in Japan.

Pine Wilt Disease: Resin flow stops 2 weeks after inoculation; transpiration is depressed; trees wilt; sapwood desiccates; foliage turns brown; tree dies 45 days later.

Damage by the Nematode (excerpt from Pine Wilt in Japan - Ministry of Agriculture, Forestry and Fisheries, Japan)

Dr. Mamiya reported (SON, 1987) that the nematode was found at only one location in Japan prior to 1930s, spread to 34 prefectures through the 1940s, and to 45 of the 47 prefectures by the 1970s. Thought to have been introduced into pine in Japan from elsewhere; pine species in Japan are very susceptible to Pine Wilt disease.

Pine forests are still healthy in cooler regions of northern Japan, so large efforts are being undertaken to prevent spread.

In North America, native conifers are mostly resistant or tolerant to B. xylophilus, and it causes little damage than on exotic pine species (Mamiya, 1983; Kiyohara and Tokushige, 1971).

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Management:

A male-produced aggregation pheromone provides opportunities for trapping and otherwise managing the vector (Teale et al., 2011; Fierke et al., 2012):

Also:

Control insect vectors with insecticides; burn infected trees.

Trunk injection of nematicides has been used in Japan, especially for valuable trees in parks, etc., but must be performed before symptoms occur. The technique has also been tested in Portugal.

Breeding resistant trees a promising approach. Species of pine vary in their resistance. Populations of the nematode differ in host preference, and response of pines differs.

Host Plant Resistance, Non-hosts and Crop Rotation alternatives:

Tree genera and species in the Pinaceae differ in their host status and tolerance to the nematode..  The presence of the nematode in wood of dead trees does not necessarilty indicate susceptibility because, besides Pinus, Monochamus spp. beetles use species of the genera Abies, Cedrus, Larix and Pices for feeding and reproduction. Consequently, transfer to nonhosts can occur.  When young trees of Abies sachalinensis (Sakhalin Fir) an Picea jezoensis (Jezo Spruce) were inoculated with the nematode, respectively 20% and 10% of the trees were killed.  In contrast, mortality was 40% and 70%, respectively, in P. densiflora and P. thunbergii.  Reproduction of the nematode in A. sachalinensis and  P. jezoensis was only about 10% of that in P. densiflora and P. thunbergii after 12 weeks of incubation in stem sections (Kasuga and Togashi (2012) indicating differences in host status and tolerance to damage.

Tolerance of selectionms made from the susceptible species Pinus densiflora and P. thunbergii:

Tolerant trees are selected from P. densiflora and P. thunbergiithat have survived pine wilt disease.Selected trees are divided into tolerance classes based on their response yo a virulent isolate of B. xylophilus. Seedlings of trees belonging to tolerant clones have been used for reforestation in Japan. The tolerance mechanism is is thought to be a high oncentration of tannin or a low pH of sap in the inner bark (Men�ndez-Guti�rrez ey al., 2017).

Procedures to disinfest transported unprocessed wood include prevention, host selection, and treatment by fumigation, irradiation, chemical dips, and elevated temperatures. (Dwinell, 1997)

Management of Pine Wilt in Japan (excerpt from Pine Wilt in Japan - Ministry of Agriculture, Forestry and Fisheries, Japan)

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References

CABI .  Data Sheets on Quarantine Pests: Bursaphelenchus xylophilus

Dwinell, L.D. 1997. Annual Review of Phytopathology 35:153-166

Mamiya, Y. 1983. Pathology of the pine wilt disease caused by Bursaphelenchus xylophilus. Annu. Rev. Phytopathol. 21, 201�220

Menendez-Gutierrez, M., K. Matsunaga and K. Togashi 2017. Relationship between pine wilt-tolerance rankings of Pinus thunbergii trees and the number of Bursaphelenchus xylophilus passing through branch sections. Nematology 19:1083-1093.

Mota, M. and P. Viera. 2004. The pinewood nematode, Bursaphelenchus xylophilus : proceedings of an international workshop, University of Evora, Portugal, August 20-22, 2001. Nematology monographs and perspectives ;v. 1. Brill, Leiden.

Soliman, T., Mounts, M.C.M., van der Werf, W., Hengeveld, C., Robinet, C., Oude Lasink. A.G.J.M. 2012. Framework for modelling economic impacts of invasive species, applied to Pine Wood Nematode in Europe.  Plos One 7: e45505. 

Teale SA, Wickham JD, Zhang F, Su J, Chen Y, Xiao W, Hanks LM, Millar JG. 2011. A male-produced aggregation pheromone of Monochamus alternatus (Coleoptera: Cerambycidae), a major vector of pine wood nematode. Journal of Economic Entomology 104:1592-1598.

Copyright © 1999 by Howard Ferris.
Revised: September 06, 2023.