Bursaphelenchus xylophilus was first described in the USA asAphelenchoides xylophilus (Steiner & Bührer, 1934). Later it was described, asB. lignicolus, when determined to be the causal agent of pine wilt disease in Japan (Mamiya & Kiyohara, 1972). The synonymy was recognized in 1981 (Nickleet al., 1981). A very similar but non-pathogenic species,B. mucronatus, was described by Mamiya & Enda (1979), differing morphologically only in minor respects fromB. xylophilus and most obviously by the presence of a mucro (finger-like projection) in the female tail terminus in the former species, which was absent in the latter. However, an intraspecific morphological variability of this character has been detected inB. xylophilus populations from North America, Asia and Portugal (Wingfieldet al., 1983; Penaset al., 2004; Guet al., 2011; Fonsecaet al., 2008). There has thus been much discussion about the taxonomic relationships between these two species, and also withB. fraudulentus Rühm, 1956, a nematode from deciduous trees in central Europe. Molecular studies of several populations of these nematodes have clearly confirmed the distinctness of the three species (Websteret al., 1990; Abadet al., 1991; Filipiaket al., 2019).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 has been shown to be an introduction from North America. In Europe, this nematode species was first identified in continental Portugal (Motaet al., 1999) and later in Spain (Abelleiraet al., 2011) and Madeira island (Fonsecaet al., 2012). Another closely related species,B. kolymensis Korenchenko, 1980 was described fromLarix from the far east of the former USSR. However, in 2011, Braaschet al. found that this species corresponds to the European type ofB. mucronatus and designated it as a subspecies,B. mucronatus kolymensis, and the East Asian type as the subspeciesB. mucronatus mucronatus.
Bursaphelenchus xylophilus
B. xylophilus is found mainly onPinus spp. that have a wide distribution in the northern hemisphere. Nevertheless, only a limited number of pine species are considered susceptible to the nematode infection; the Far Eastern speciesP. bungeana, P. densiflora, P. luchuensis, P. massoniana andP. thunbergii (in their native habitats), and the European speciesP. mugo,P. nigra,P. sylvestris andP. pinaster are the species known to be killed by the nematode as mature trees in the field (Evanset al., 1996). In Spain,P. radiata was also considered as a host species under European conditions (Zamoraet al., 2015). Inversely, stone pine (P. pinea) has never been found infected byB. xylophilus even in locations with high incidence of the pathogen, which has led to the assumption that it is tolerant/resistant under natural conditions (Naveset al., 2018). Many other species have been found to be damaged or killed by the nematode but only under experimental conditions (mainly as seedlings in glasshouses). Other conifers can also act as hosts (Abies, Cedrus, Larix,Picea and Pseudotsuga) but reports of damage are rare. Within the EPPO region,P. sylvestris would be the species ofPinus most at risk in northern and central areas, whereasP. nigra andP. pinaster would be threatened in central and southern areas.
Monochamus spp.
TheMonochamus spp., which are of concern as known or possible vectors ofB. xylophilus, mainly develop inPinus species, but other coniferous genera can also act as hosts (see Table 1). In addition,Monochamus spp. will oviposit in most coniferous species, even those in which they may not be able to complete development to adult stages. The most important hosts ofM. galloprovincialis, the European vector ofB. xylophilus, are pines, mainlyP. sylvestris,P. nigra,P. halepensis andP. pinaster, but alsoP. brutia, P. peuce andP. mugo, and spruce (Picea). The remaining European members of theMonochamus genus prefer other conifers, such as fir (Abies), larch (Larix) and spruce (Naveset al., 2016). Some conifers appear to be unsuitable hosts andThuja plicata has insecticidal properties that prevent oviposition. Other species ofMonochamus attack other plant hosts, such as broadleaf, coffee and cocoa trees, but are not relevant in the present context.
Host list:Abies balsamea,Abies,Cedrus atlantica,Cedrus deodara,Cedrus,Larix decidua,Larix gmelinii var. olgensis,Larix gmelinii var. principis-ruprechtii,Larix kaempferi,Larix laricina,Larix,Picea abies,Picea pungens,Pinus armandii,Pinus banksiana,Pinus bungeana,Pinus cembra,Pinus clausa,Pinus contorta var. murrayana,Pinus densiflora,Pinus echinata,Pinus elliottii,Pinus koraiensis,Pinus lambertiana,Pinus luchuensis,Pinus massoniana,Pinus mugo,Pinus nigra,Pinus palustris,Pinus pinaster subsp. escarena,Pinus pinaster,Pinus ponderosa,Pinus radiata,Pinus resinosa,Pinus strobus,Pinus sylvestris,Pinus tabuliformis,Pinus taeda,Pinus thunbergii,Pinus virginiana,Pinus yunnanensis,Pinus,Pseudotsuga menziesii,Pseudotsuga,Tsuga canadensis,TsugaBursaphelenchus xylophilus
It is presumed thatB. xylophilus originated in North America and was transported from there to the southern Japanese island of Kyushu in infected timber in the beginning of the 20th century (Nickleet al., 1981; Mamiya, 1983; Malek & Appleby, 1984). The fact that native American conifers are mostly resistant, whereas Japanese species are susceptible, tends to support this view. From Japan,B. xylophilus has spread to other Asian countries (Liet al., 1983) and then, at the end of the 20th century, it was introduced in Europe, in Portugal (mainland and Madeira island) and Spain (isolated outbreaks) (Motaet al., 1999; Abelleiraet al., 2011; Fonsecaet al., 2012).
Monochamus spp.
The species ofMonochamus which are of concern as known or possible vectors ofB. xylophilus occur only in the northern hemisphere. A list, showing their geographical distribution, whether their range currently overlaps with that ofB. xylophilus and whether they are known to be vectors ofB. xylophilus is provided (Table 1). It may be noted that many species are very widely distributed, and the genus is represented in most areas of the northern hemisphere. Exceptions are the islands of Great Britain and Ireland. The genusMonochamus is represented elsewhere in the world, but the species concerned do not attack conifers.
Bursaphelenchus xylophilus
B. xylophilus is transmitted from one host to a new host by species ofMonochamus, the insect vectors (see section onMonochamus spp. below). The transmission can be accomplished during the insect maturation feeding period on healthy trees, designated as primary transmission, or during the oviposition activity of the female vector on trees which recently died or weakened trees and known as secondary transmission (Naveset al., 2016).
The primary transmission is the most important pathway in regions whereB. xylophilus was introduced (Asia and Europe), due to the occurrence of susceptible plant hosts, while in North America the secondary transmission is the most frequent pathway for nematode dissemination.
The life cycle of these nematodes, that comprises eggs, four juvenile stages (J1, inside the egg, J2, J3, J4) and adults with sexual dimorphism (the propagative forms) and four moults, can occur in the phytophagous phase (nematodes feed on cells of healthy trees) and in the mycophagous phase (nematodes feed on fungi).
When the environmental conditions are adverse, such as periods of desiccation or food shortage, morphological and physiological changes occur in the second-stage juveniles (J2) to give rise to the third and fourth dispersal stages (JIII and JIV) also designated as ‘pre-dauer’ and ‘dauer’ juveniles respectively. The JIII are attracted to the pupal chambers of the insects and moult into non-feeding JIV that are adapted to be carried out mainly in the tracheal system of immature adult insect vectors, entering through the spiracles, before the insect’s emergence from the wood. Nematodes JIV can also be found in other body segments, head, antennae and wings, using fungal hyphae, present in the interior of the pupal chambers, to achieve proximity to the immature adult beetle.
After the emergence, the infested insects feed on young branches of a new host and transmit the JIV (primary transmission) that penetrate through the feeding wounds and moult into adults within 48 hours. Afterwards, the nematodes reproduce rapidly and migrate through the vascular system, entering the conductive vessels, responsible for the circulation of water and minerals (crude sap), and feed on parenchyma and epithelial cells of the resin canals (phytophagous phase) causing cavitation and embolism of tracheids that stop the sap circulation. A decrease in foliar transpiration, needle discoloration, wilting, and death of the tree can be seen within two or three months of the initial infection (Vicenteet al., 2012; Futai, 2013).
In the laboratory,B. xylophilus can be maintained on fungal (Botrytis cinerea) cultures. The nematodes reproduce in 12 days at 15°C, 6 days at 20°C and 3 days at 30°C and the females lays on average 79 eggs in 28 days. The second-stage-juveniles (J2) hatch in 26-32 h at 25°C. The temperature threshold for development is 9.5°C (Futai, 1980, 2013).
Monochamus spp.
Species ofMonochamus inhabiting conifers are the principal vectors ofB. xylophilus worldwide,M. alternatus being the major vector in Asia, whereasM. carolinensis andM. scutellatus are the major vectors in North America. In Europe (Portugal and Spain),M. galloprovincialis is the main vector. Other less efficientMonochamus vectors have been recorded in Japan and North America (Table 1). Many of theMonochamus spp. from conifers have been recorded as having non-pathogenicBursaphelenchus spp. as associates; it is supposed, therefore, that most, if not all, species would also be capable of transmission ofB. xylophilus to a greater or lesser extent.
Other genera of the Cerambycidae (e.g.Acalolepta, Acanthocinus, Amniscus, Arhopalus, Aromia, Asemum, Corymbya, Neacanthocinus, Rhagium, Spondylis, Uraecha, Xylotrechus) and other Coleoptera (e.g.Chrysobothris, Hylobius, Odontotermes, Pissodes,Tomicus) have been found to carry B. xylophilus in or on their bodies, but there is no evidence that they have any role as vectors in nature. In Europe,B. xylophilus has never been found associated with insects of any of these genera (Naveset al., 2016).
The life cycle ofMonochamus species comprises eggs, a variable number of larval instars, pupae and adults.Monochamus alternatus,M. galloprovincialis andM. scutellatus have four larval instars, whereasM. sutor has a fifth instar and three to eight larval instars have been recorded forM. carolinensis.
The selection of the egg-laying site is made by the female, based on characteristics of the host such as bark thickness and moisture content of the sapwood. Adult females excavate small niches, known as ‘egg-pits’, in the bark, with their mandibles, and use the ovipositor to insert the egg under the bark, on the cambium/sapwood interface, plugging the oviposition scar with a gelatinous substance to protect it from fungi and adverse environmental conditions. Due to the relatively small size of the ovipositor, bark which is more than a few millimetres thick is a limiting factor. Usually, the egg-pits have a single egg, although two or three can also be found, while many do not contain eggs. Females can live for up to 113 days laying 40 to more than 300 eggs during a lifetime. In general, bigger females live longer and lay more eggs.
After the laying of the eggs, the larvae hatch within six to 21 days, depending on the environmental temperature. The first two larval instars (L1 and L2) feed on the phloem and cambium tissues under the bark, constructing asymmetrical galleries which can have lengths of 15 cm or more, becoming obstructed by frass and excrements over time. The third instar larva (L3) starts to bore into the xylem through an oval hole, making an internal gallery, which is usually U-shaped or S-shaped, or has an intermediate form. Later, larval instars complete the gallery by digging an enlarged pupal chamber (usually within less than 20 mm) close to the wood surface. Then, the larvae plug the opening with coarse fibrous debris, and some species enter a period of dormancy (diapause) for several months, experiencing visible physiological and morphological changes in body coloration (from milky white with faecal material to vivid yellowing without faecal material), while ceasing feeding. After the cold season, the mature larvae undergo morphological and physiological changes and moult into pupae.
The pupal stage lasts for two or three weeks and when the adult insect is fully sclerotized, it emerges from the pupal chamber through a round hole (about 4-12 mm in diameter) at the wood surface.
The newly emerged sexually immature adults fly to healthy trees to feed on the bark and phloem tissues of small branches (maturation feeding). This feeding period is essential for sexual maturation, and extends for the first 10-20 days after emergence, although adultMonochamus will continue feeding on conifer tissues throughout their lives. Mature adults are attracted to weakened host trees or recently felled logs where they mate, and females start laying eggs.
EuropeanMonochamus species share similar phenology and are typically univoltine, completing their life cycle in one or two-years. Latitude and altitude have influence on the length of the lifecycle, which is related to variations in mean annual temperatures (Naveset al., 2016).Monochamus alternatus andM. galloprovincialis usually have one generation per year while the North AmericanM. carolinensis can have up to two annual generations.
Bursaphelenchus xylophilus
The symptoms in the trees infected byB. xylophilus are not specific. However, the first indication of the presence of nematodes in the tree is a reduction of resin exudation, due to the disruption of the resin canals and to the diffusion of oleoresins into tracheids. Another symptom is the yellowing and wilting of the needles, partial or total dryness of the crown leading to eventual death of the tree, which is variable according to the host plant, temperature and time of the year. In some trees the infection withB. xylophilus does not lead to expression of wilt symptoms (asymptomatic trees). Details are given in PM 9/1 (6)Bursaphelenchus xylophilus and its vectors: procedures for official control EPPO, 2018).
Monochamus spp.
These insects only oviposit on recently felled trees and logs or trees already under stress. The larval instars feeding produces large galleries on the sapwood under the bark and bore holes into the wood. The emergence of immature adults give rise to a round hole, but other insects, such asSirex spp. wood-wasps andXilocopa spp. carpenter bees, can cause similar exit holes.
Bursaphelenchus xylophilus
B. xylophilus has the general characters of the genusBursaphelenchus (Nickle, 1970; Hunt, 1993): small to long and slender nematodes; cephalic region high and offset by a constriction, with six lips; stylet well developed (length less than 30 µm), usually with weak basal knobs; median bulb or metacorpus, oval to quadrangular, well developed; oesophageal glands overlapping the intestine.
Female
Female with post-uterine sac, usually three to six body widths in length; vulva with a conspicuous overlapping anterior lip (vulval flap); usually at 70–80% of the body length; tail sub‐cylindrical and, in most populations, with a broadly rounded terminus.
Male
Male tail with a strong dorsal curvature; small terminal bursa at the tail tip; robust spicules, strongly arcuate with large rounded apex and a prominent rostrum; spicules tip with a disc‐like projection (cucullus); gubernaculum absent; seven caudal papillae (one adanal pair, just pre-anal, a single papilla just pre-anal centered and two post‐anal pairs).
B. xylophilus can be distinguished by three main characters. In males, spicules with a cucullus and in females, vulva with vulval flap plus a rounded tail terminus. This last character has been considered as the main morphological character to differentiateB. xylophilus from the non-pathogenic speciesB. mucronatus that has a mucro at the posterior end (mucronate tail). However, an intraspecific morphological variability of this character has been detected.
Measurements of morphological characters ofB. xylophilus are given in the Diagnostic Protocol PM 7/4 (3) Bursaphelenchus xylophilus (EPPO, 2023) along with information on identification by molecular methods.
Monochamus spp.
Eggs
The eggs, in general 4.0 mm long by 1.2 mm wide, are elongate, slightly rounded at the poles, and the chorion has a fine, faint reticulate sculpture. Initially, eggs are white and matt, acquiring a light-brownish colouration over time.
Larvae
The larvae are robust, legless, and have a white or yellowish white and opaque coloration, with small black and red hairs all over the body, and an amber-black head capsule with well-developed chewing mouthparts. Body is elongate, soft, with ten abdominal segments, including the anal mamilla, and all abdominal tergites are simple, without spines or sclerified plates.
Pupae
The pupae initially have a white colour and a few days before adult’s emergence become darker with a harder outer cuticle. This development stage morphologically resembles the adults, with visible mouthparts, legs, antennae and wings.
Adults
Adults are 15 to 32.8 mm long (without antennae). Characteristics of the genus are: forehead transversal or sub-square; antennal protrusions very high, close together and separated by a deep hollow. Antennae slender, very long for the male, distinctly longer than body for the female, the third segment being at least twice the length of the scape. Pronotum slightly convex, with a broad collar margin and a broad basilar margin marked by a groove, each side with a large lateral submedian conical protuberance. Anterior coxal cavities opening rearwards. Prosternal protuberances rounded, lower than coxae. Mesosternal process narrow. Elytra wider than pronotum at the base, shoulders protuberant, apices obsoletely truncated. Legs thin and elongate, especially in males where the anterior tibia is arched, and tarsi bordered by hairs.
Bursaphelenchus xylophilus
Before any symptoms appear in trees suspected of being infected, the reduction of oleoresin production can be detected by making a hole 10-15 mm in diameter through the bark and cambium, due to the rupture of the resin canals and to the dissemination of oleoresins into adjacent tracheids. Nematodes can be extracted from trees, by collecting wood samples from different zones, including the upper part of the trunk and the crown. Guidance on sampling is given in EPPO Standard PM 9/1 (6) (EPPO, 2018a). Afterwards, wood samples should reach an incubation temperature of approximately 25°C for at least 14 days to allow any nematodes present to breed and maximise the likelihood of detection. Then, nematodes can be extracted from the samples (wood ships, shavings, sawdust, branches) using the standard nematode extraction method (Baermann funnel method) or modifications (Whitehead and Hemming tray method) for 48 h. These methods are based on the motility of the nematodes that migrate, at room temperature, from the wood into the water. Guidance on nematode extraction is given in EPPO Standard PM 7/119 (1) (EPPO, 2013).
The fourth dispersal juvenile stage (IV) can be extracted from the vectors by cutting the insects into pieces and using the Baermann funnel extraction method over 24 h (EPPO, 2013).
Monochamus spp.
The conical oviposition scars (egg-pits) on the bark can indicate where the eggs have been laid. Egg-pits are flat and slit-like when the bark is thin and assume a pit-like structure on wood sections with thicker bark. When the bark is removed, sinuous galleries made by young larvae (L1 and L2), during their feeding activity, can be seen on the sapwood. These galleries remain detectable for several years after the larvae´s presence. The third larval instar (L3) begin tunneling in the heartwood (xylem) by boring an oval hole and the majority of the fourth instar larval (L4) are found in the heartwood galleries. The pupal chamber, constructed by the last-instar larvae, is usually located near the wood surface to enable the subsequent emergence of the adults. The more distinct circular holes of the adults, visible at the wood surface, are the exit holes of the adults, indicating that the insects have completed their development in the wood and have emerged. Traps and lures are highly effective for monitoringMonochamus flying adults and are efficient tools to sample populations in the field (Torres-Vilaet al., 2015).
The nematodes, within the wood tissues, can move actively and can leave one part of wood to move into an adjoining part., However, they need an insect vector to move from one host tree to another. Adults of the vector beetles can fly actively, and a peak of flight activity is reached about 5 days after emergence. In dense woodland, the flights of the beetles are short but, in more open areas and/or in the absence of suitable hosts, long dispersal flights (>2 km up to 40 km or longer) have been recorded (Kobayashiet al., 1984).
Infected wood is the most probable mean of international transport ofB. xylophilus, and the species has been intercepted on a few occasions on sawn wood, round wood and wood chips imported into the EPPO region from the USA, Canada and Asia.
The most likely pathway of introduction ofB. xylophilus is when imported together with insect vectors which may carry and transmit the nematodes to coniferous trees. MatureMonochamus larvae can survive in processed timber for several months and can be transported over long distances with international trade of goods and merchandise, being occasionally found alive in assorted and untreated wood packaging material (Sousaet al. 2011a). Survival of the larvae is higher on larger pieces of timber and, therefore, round wood and sawn wood present a greater risk than smaller pieces of wood. Wood chips can have a high moisture content, allowing nematode survival, but the shredding of the wood to small sections reduces the possibility of insect vectors surviving.
Whether introduced with or without a vector insect, it is still necessary for long-term establishment for the nematode to find a mean of coming into contact with an insect vector, and this can probably only be achieved if the nematode first invades wood which contains larvae or pupae of a potential vector. Nematodes can survive for long periods in wood and they can move from infected wood to timber or damage trees (Sousaet al., 2011b; Hopz-Bizikset al., 2017).
Bursaphelenchus xylophilus
Pine wilt disease was first reported in Japan in 1905 in Nagasaki, Kyushu, but the causal agent was only identified asBursaphelenchus sp. in 1971 (Kiyohara & Tokushige, 1971). In 1972, the species was described asB. lignicolus in Japan (Mamiya & Kiyohara, 1972) and then synonymized asB. xylophilus (Nickleet al., 1981). 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, reaching 2.4 million m3 of annual timber loss in the late 1940s (Mamiya, 1988), and now being on average of 1 million m3/year (Suzuki, 2002).
In 1979,B. xylophilus was associated with the death ofPinus trees in Missouri (USA), primarily ofP. sylvestris growing in amenity plantings (Malek & Appleby, 1984), and, in North America in general, losses arise almost exclusively among exotic species and in artificial forest ecosystems like ornamental conifer plantings, wind-breaks and Christmas tree plantations.B. xylophilus is widespread in natural coniferous forests but significant losses are not recorded.
In China, in a year, tree mortality reached 2.3 million just in a single county (Robinetet al., 2009) with over one million trees killed/year from 1995 to 2006 (Zhao, 2008) while in South Korea over one million trees were affected by pine wilt disease in 2005–2006 (Shin, 2008).
Predicted losses in wood production in the European Union from the spread and damage fromB. xylophilus were estimated at 22 billion euros over 22 years, with losses in standing volume in Portugal and Spain greater than 80% (Solimanet al., 2012).
Monochamus spp.
Monochamus larvae can cause economic losses to felled logs by boring holes in the wood, which is normally only of significance if the logs are left for a long time in the forest after felling. Most European species appear to be attracted to scorched and slightly burned trees after forest fires, where they can cause significant damage to the wood (Naveset al., 2016). Under well-managed forest conditions,Monochamus spp. are not generally considered to be serious pests, although they can occasionally demonstrate aggressive behaviour as a result of outbreaks with very high population levels (Hellrigl, 1971). During outbreaks in the boreal forests of Russia, the maturation feeding by millions of insects caused severe crown damage, leading to tree weakening which predisposed the trees to subsequent attacks by other pests (Gavrikov & Vetrova 1991). Nevertheless, in general, the only economic impact arises in countries whereB. xylophilus is present and localMonochamus species transmit the nematode to healthy hosts.
The tactics and strategies developed to manage pine wilt disease rely on the control of the insect vector and the nematode, with complementary approaches designed to reduce the impact of both organisms (Naveset al., 2016). So far, it has proved impossible to controlB. xylophilus 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 (e.g. religious) significance, infection can be prevented by a prophylactic chemical treatment. Research is continuing to search for effective management strategies for the insect vector while inside the host tree [i.e. mechanical (felling the trees, elimination of plant material, soaking in water), chemical (treatment of wood, protection with insecticide nets), biological (parasitoids, entomopathogenic fungi and microsporidia, entomopathogenic nematodes, predators)], as well as for the insect vector while outside the host tree [i.e. biotechnical (kairomones, pheromones, traps), chemical (insecticides spraying and tree or soil injection), biological (entomopathogenic fungi, entomopathogenic nematodes and bacteria, predators), others (moulting inhibitors and adult sterilization)]. For the insect-host tree interaction, the strategies can be based on chemical (feeding repellents and inhibitors, oviposition inductors) methods. Concerning the nematodes, management strategies can be based on chemical (fumigation), biological (nematophagous fungi), heat and irradiation treatments while for the nematode-host tree interaction there are chemical possibilities (nematicides and biocides). A long-term strategy is the breeding for resistance/tolerance of pine species/varieties, which has been initiated in eastern Asia and in Europe.
B. xylophilus is included in the EPPO A2 list of pests recommended for regulation as quarantine pest. It is a quarantine pest for the European Union and many other EPPO member countries. The risk of introduction into other countries of the EPPO region is high and Evanset al. (2009) prepared a detailed report of a Pest Risk Analysis for B. xylophilus. EuropeanPinus species have proved very susceptible in North America and the introduction ofB. xylophilus into other areas of Europe is considered a very serious risk. Several species ofMonochamus are present in Europe (Table 1). In view of the non-specific nature of the phoretic relationship betweenMonochamus andBursaphelenchus spp., it is probable that these European species would transmitB. xylophilus. Since the disease is favoured by hot summers, areas in the Southern EPPO region are most at risk. Direct introduction of the nematode into the Northern EPPO region certainly also presents a risk, since symptoms could be expressed when trees suffer from any other form of stress (e.g. drought or occasional periods of high temperatures).
EPPO's recommendations to prevent the introduction of B. xylophilus and its vectors from countries where the nematode occurs are detailed in PM 8/2 (3) Coniferae (EPPO, 2018). These recommendations cover plants for planting, cut branches, wood (round wood and sawn wood), particle wood (wood chips, hog wood) and isolated bark of Coniferae. For wood packaging material (including dunnage), the requirements of ISPM 15 (FAO, 2019) should be fulfilled to prevent the introduction ofB. xylophilus (and other pests) via international trade into new areas.
Several quarantine treatments for round wood, sawn wood, wood chips, isolated bark and wood packaging materials have been proposed, such as steam/heat treatment or irradiation according to PM 8/2 (3) Coniferae (EPPO, 2018b). 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.
The only known effective treatment for wood already infected withB. 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 min. However,B. xylophilus can colonize heat-treated timber if kept in direct contact with nematode-infected timber, although infection can be prevented by kiln-drying (KD) the wood to moisture content around 18-22%, thus hampering nematode transfer (Sousaet al., 2011b). After heat-treatment and kiln-dry, old and dry wood does not support re-infection withB. xylophilus even in favorable conditions (Naveset al., 2019). Visual inspection of timber does not always reveal the presence of insect larvae or pupae, which can be hidden within internal galleries, but they can be detected by X-ray analysis.
Table 1. Monochamus species from coniferous trees, known to be vectors ofBursaphelenchus xylophilus or considered to be potential vectors.
Monochamus species | Geographical distribution | Main hosts | Vector status |
North America | |||
M. carolinensis Olivier | Canada, Mexico, USA | Pinus banksiana, P. clausa, P. nigra, P. ponderosa, P. resinosa, P. strobus, P. sylvestris, | + |
M. clamator LeConte | Canada, USA | Pinus contorta | - |
M. marmorator Kirby | Canada, USA | Abies balsamea | + |
M. mutator LeConte | Canada, USA | Pinus nigra, P. resinosa | + |
M. notatus (Drury) | Canada, USA | Pinus strobus | - |
M. obtusus Casey | Canada, USA | Abies, Pinus, Pseudotsuga | - |
M. rubigeneus Bates | Guatemala, Honduras, Mexico, USA | Pinus | - |
M. scutellatus Say subsp.scutellatus | Mexico, USA | Abies, Larix, Picea, Pinus | + |
M. scutellatus subsp.oregonensis LeConte | Canada, USA | Picea | - |
M. titillator (Fabricius) | Canada, USA | Abies, Picea, Pinus strobus, P. sylvestris, P. thunbergii | + |
Palaearctic region (overlapping withB. xylophilus in some countries/regions) | |||
M. alternatus Hope | China, Korea, Japan, Taiwan | Abies, Cedrus, Larix Picea, Pinus densiflora, P. luchuensis, P. thunbergii, | + |
M. galloprovincialis (Olivier) | Belgium, Finland, France, Germany, Greece, Iraq, Italy, Kazakhstan, Kyrgyzstan, Mongolia, North Africa, Poland, Portugal, Russia, Sweden, Turkey | Pinus | + |
M. saltuarius Eschscholz | China, Europe (central & eastern and south Italy), Korea, Japan, Siberia, Taiwan | Picea, Pinus densiflora, P. thunbergii | + |
M. tesserula White | China, Japan | Pinus | - |
M. rosenmuelleri Cederhielm | China, Finland, Japan, Poland, Russia (Caucasus), Siberia | Abies, Larix, Picea, Pinus | - |
Palaearctic region (not overlapping with B. xylophilus) | |||
M. sartor Fabricius | Europe (eastern France to western Ukraine) | Picea, Pinus | - |
M. sutor (Linnaeus) | China, Europe (north, central & eastern), Georgia, Kazakhstan, Mongolia, Russia (European), Siberia | Larix, Picea, Pinus | - |
+ Known vector; - Potential vector
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This datasheet was extensively revised in 2019 by Isabel Abrantes and Luís Fonseca from Centre for Functional Ecology (CFE), Department of Life Sciences, University of Coimbra, Portugal, and Pedro Naves from National Institute for Agricultural and Veterinary Research (INIAV), Oeiras, Portugal. Their valuable contribution is gratefully acknowledged.
This datasheet was first published in the EPPO Bulletin in 1986 and revised in the two editions of 'Quarantine Pests for Europe' in 1992 and 1997, as well as in 2019. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.
CABI/EPPO (1992/1997)Quarantine Pests for Europe (1st and 2nd edition). CABI, Wallingford (GB).
EPPO (1986) Data sheets on quarantine organisms No. 158,Bursaphelenchus xylophilus. Bulletin OEPP/EPPO Bulletin 16(1), 55-60.
