Bursaphelenchus xylophilus

 

Contents

 

Rev 12/27/2013

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
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Classification:

Chromadorea
Rhabditida
Tylenchina
Aphelenchoidea
Aphelenchoididae
Bursaphelenchinae
     Bursaphelenchinae

                    Bursaphelenchus xylophilus

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.

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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).

 

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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; 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.

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 nematodeIt can also be vectored 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

M. scutellatus male

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.

M. scutellatus female Female

Cerambycid grub 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 Indicators

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:

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

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). 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):

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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.

For an extensive list of host plant species and their susceptibility, copy the name

Bursaphelenchus xylophilus

select Nemabase and paste the name in the Genus and species box

 

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Life Cycle:

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

Dauer larvae carried most frequently by Pine Sawyer beetles (M. alternatus) in Japan and 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.

Phoresy

Phoretic relationship of insect and nematode

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

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.

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.

Nematode Damage

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.

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Management:

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.

Resistance

For a list of plant species or cultivars (if any) reported to be immune or to have some level of resistance to this nematode species, copy the name

Bursaphelenchus xylophilus 

select Nemabase Resistance Search and paste the name in the Genus and species box

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

Pine Wilt Management

Management of Pine Wilt in Japan

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

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References

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

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

CABI .  Data Sheets on Quarantine Pests: Bursaphelenchus xylophilus

Movie:  Pine Wilt Nematode. Japanese Forestry Agency, Ministry of Agriculture, Forestry and Fisheries, Japan.

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.
 

 
Copyright © 1999 by Howard Ferris.
Revised: December 27, 2013.