Taxonomic name: Bursaphelenchus xylophilus (Steiner & Buhrer) Nickle
Synonyms: Aphelenchoides xylophilus , Bursaphelenchus lignicolus
Common names: pinewood nematode
Organism type: nematode
The pinewood nematode, Bursaphelenchus xylophilus is the causative agent of pine wilt disease. Vectors of this nematode are long-horned beetles especially those belonging to the genus Monochamus. The introduction of this nematode into Japan had devastating effects on the native pines in that country. Most species of conifers endemic to North America are resistant to the wilt disease, but many exotic species are highly susceptible.
The University of Illinois Department of Crop Sciences (1998) states that, "Accurate B. xylophilus identification requires microscopic examination because other species of nematodes frequently inhabit dead or diseased wood." The authors go on to state that, "The most prominent symptom of B. xylophilus is the sudden decline and death of the entire tree within a few weeks or months after the first sign of disease. Symptom development is most rapid and uniform over the tree during the warmest months of the year, when the needles seemingly die all at once and in young to middle-aged trees. The foliage of the infected tree passes from the normal, healthy green through four stages of discolouration. The needles first turn light grayish green. By this time, resin no longer flows from the wood and the tree is already dead. The overall colour of the tree then proceeds to a yellowish green as chlorophyll begins to disappear from needles, then to a yellowish brown as the remaining chlorophyll is lost, and finally to a total brown. Longer and softer-needled species of pines show an obvious wilt of needles over the entire tree, as if its source of moisture has been suddenly cut off. Because death is so rapid, the tree retains its brown needles for a long period of time, often up to a year. Thus, wilt-killed pines stand out prominently among healthy neighboring pines."
Ichihara et al. (2002) state that, "Fukuda (1997) divided the symptom development into an early stage and an advanced stage. In the early stage, B. xylophilus invasion induces cytological changes in pine stems as a defense reaction, resulting in partial cavitations within tracheids. In the advanced stage, a complete cessation of water conduction within the xylem occurs, resulting in physiological changes in needles such as a marked decrease in leaf water potential, and in both photosynthetic and transpiration rates. Sakuta et al. (1994) reported that roots stopped growing on the sixth day after B. xylophilus inoculation in Pinus thunbergii seedlings."
Please see PaDIL (Pests and Diseases Image Library) Species Content Page Non-insects Pine Wilt Nematode for high quality diagnostic and overview images.
natural forests, planted forests
Dwinnel (1986) states that, adult pine sawyers (Monochamus spp.), which are woodborers, are vectors of B. xylophilus and other species of Bursaphelenchus. The borers colonise pine logs held in storage or pines weakened or killed by natural or manmade stresses." The University of Illinois Department of Crop Sciences (1998) states that, "Virtually all species of pine grown east of the Rocky Mountains are known hosts of the B. xylophilus. The species differs widely, however, in their susceptibility to B. xylophilus. Fortunately, native American pines are relatively resistant. Thus, B. xylophilus does not appear to be as serious a threat to pine forests in this country as it is to those in Japan, where the native pines are highly susceptible. The disease does not occur in conifers other than pines, although the nematode has been found occasionally in white and blue spruce, balsam fir, eastern and European larch, and Atlas and deodar cedar."
Sousa et al. (2002) state that, "Several other insects have also been described worldwide to carry B. xylophilus: 21 species of Cerambycidae, two species of Curculionidae and one genus of Buprestidae (Linit, 1988, in Sousa et al. 2002)." Sousa et al. (2002) state that their results, "Showed that M. galloprovincialis is the only vector of B. xylophilus in Portugal."
Native range: North America (APHIS, 1999)
Known introduced range: Asia, and Europe (APHIS, 1999)
Introduction pathways to new locations
Forestry: APHIS (1999) notes that, "It was analysed that the wooden packing materials imported from the infected countries caused the infection. Remote spread of B. xylophilus is by means of the imported plants, wood, wood product and packing materials."
Local dispersal methods
On animals: APHIS (1999) notes that, "The natural spread of Bursaphelenchus xylophilus is by means of the food and reproduction activities of the media Monochamus spp."
Skarmoutsos and Skarmoutsos (2000) state that, "B. xylophilus is a quarantine pest for the European Union under Directive 77/93/EEC (Anonymous 1993)." The EPPO Bulletin (2003) reports that, "B. xylophilus is an EPPO A1 pest." The bulletin sets out pest-specific phytosanitary requirements for and its vectors, this covers plants for planting, cut
branches, isolated bark and various types of wood (squared wood, round wood, packaging wood, particle wood and waste wood) of coniferous species generally.
Samples from 3416 batches of wooden packaging material were inspected for the presence of nematodes in the Ningbo Entry–Exit Inspection and Quarantine Bureau, China between January 2003 to June 2005. Bursaphelenchus spp. were detected in 202 batches from 25 different countries, species detected include B. xylophilus, B. fungivorus, B. rainulfi, B. hylobianum, B. thailandae, B. mucronatus, B. aberrans, B. lini, B. singaporensis, B. doui, B. conicaudatus, B. vallesianus, B. pinasteri, B. hofmanni and B. arthuri. The most frequently found species were B. mucronatus, B. xylophilus, B. fungivorus, B. rainulfi and B. thailandae.
B. xylophilus was not only found in packaging wood imported from areas where it is known to occur (i.e. The United States of America, Japan, Korea, Hong Kong and Taiwan), but also from countries considered to be free of this dangerous pest (i.e. Brazil, Thailand, Belgium, The Netherlands, Italy and Spain).
The authors state that, " The occurrence of B. xylophilus in packaging wood from countries regarded as being free of the nematode can most likely be explained by the global circulation of wooden packaging material among infested and non-infested countries. Our findings emphasise the need to fully implement international standards on phytosanitary treatment of packaging wood, in order to prevent further spread of the pine wood nematode, and the need for careful re-examination of the current heat treatment measures". (Abstract: Gu et al. 2006)
In 2002, United Nation FAO's (Food and Agriculture Organisation) Interim Commission on Phytosanitary Measures imposed a global standard for treating wood packaging International Standard for Phytosanitary Measures No. 15 to stop the spread of invasives, that are now being adopted by individual countries.
For details on management of this species including physical, biological and chemical control please management information.
The American Phytopathological Society (APS) offers on its website illustrated lessons to introduce the symptoms and signs, pathogen biology, disease cycle, epidemiology, disease management, and scientific, economic and social significance of major plant diseases. Please follow this link
Pine wilt disease for details.
Asai & Futai (2001) conducted a study that suggests that, "The exposure to air pollutants including acid rain might reduce the resistance of pine trees and might lead to their death. In the present study, exposure to sulfur acid rain over 1 year accelerated the disease development in Japanese black pine, whereas exposure to sulfur acid rain over 2 years did not break the tolerance of Japanese red pine trees to pinewood nematode. These results suggest that acid rain is a weak promoting factor of the pine wilt disease." The University of Illinois Department of Crop Sciences (1998) states that, "The adults (of B. xylophilus) feed on the thin-walled cells lining the resin canals."
The University of Illinois Department of Crop Sciences (1998) states that, "B. xylophilus has the shortest life cycle of any plant-parasitic nematode, resulting in a population explosion within highly susceptible pines. One generation is completed in four days when the nematode is cultured on fungi in its optimum. During the warm summer months, B. xylophilus reproduce rapidly to very high numbers. They spread throughout the resin canal system of susceptible pines, into the trunk and virtually all branches, and even into the roots. When live tree cells are no longer available,B. xylophilus continue to feed and reproduce on the fungal hyphae that grow through the resin canals. B. xylophilus become inactive in late fall and over winter in the wood of both live and dead trees. Activity resumes in the spring."
The following life cycle information has been summarised from the University of Illinois Department of Crop Sciences report on B. xylophilus (1998). The B. xylophilus disease cycle is highly complex, involving at least four different organisms. Infection of healthy pines results from a unique relationship between B. xylophilus and a sawyer beetle in the genus Monochamus. The dispersal-stage B. xylophilus accumulate around the pupation chamber (of the sawyer beetle) and molt to more specialised, non-feeding fourth-stage juveniles, called dauer larvae. B. xylophilus enter the beetle through its spiracles, or breathing pores, and mass within its tracheae, or breathing tubes. The beetle then chews its way out of the wood, carrying large numbers of B. xylophilus in a quiescent state in its respiratory system. Soon after emergence from the dead wood, the beetle flies to a live pine and feeds on the branches. B. xylophilus emerge from the beetle spiracles and enter the tree through the feeding wounds in the branches. B. xylophilus migrate to the resin canals of the pine and molt to adults. The adults begin to feed on the thin-walled cells lining the canals. The adults mate and females begin laying eggs in the resin canals. The juvenile nematode molts once within the eggs, hatches as a second-stage juvenile, and passes through two additional feeding stages before a final molt to the adult stage. This normal life cycle without production of dispersal and dauer larva stages then continues, building up the nematode population in the tree (University of Illinois Department of Crop Sciences, 1998). (Dauer or dauer larva refers to a special larval stage of nematodes at which the animal changes its structure to adapt to an unfavourable environment such as lack of food or high population density. Dauer larvae do not feed but can survive a much longer period of time than non-dauer nematodes do).
As the wood of the dead pine dries, begins to decay, and generally becomes inhospitable to the nematode, reproduction ceases and the second stage juvenile molts to the dispersal stage, rather than to the normal third-stage juvenile (Kosaka, Hajime., pers.comm., 2005).
Reviewed by: Hajime Kosaka. Hokkaido Research Center Forestry and Forest Products Research Institute Japan
Principal sources: European and Mediterranean Plant Protection Organisation (EPPO). 2002. Bursaphelenchus xylophilus and its vectors: procedures for official control. Bulletin OEPP/EPPO Bulletin
Pine Wilt Disease University of Illinois Department of Crop Sciences, 1998
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Monday, 14 August 2006