Xyleborinus saxesenii (fruit-tree pinhole borer)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact Summary
- Economic Impact
- Impact: Biodiversity
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Links to Websites
- Distribution Maps
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IdentityTop of page
Preferred Scientific Name
- Xyleborinus saxesenii (Ratzeburg)
Preferred Common Name
- fruit-tree pinhole borer
Other Scientific Names
- Bostrichus saxesenii Ratzeburg
- Tomicus decolor Boieldieu
- Tomicus dohrni Wollaston
- Xyleborinus librocedri Swaine
- Xyleborinus saxeseni (Ratzeburg)
- Xyleborinus tsugae Swaine
- Xyleborus aesculi Ferrari
- Xyleborus angustatus Eichhoff
- Xyleborus arbuti Hopkins
- Xyleborus floridensis Hopkins
- Xyleborus frigidus Blackburn
- Xyleborus paraguayensis Schedl
- Xyleborus pecanus Hopkins
- Xyleborus peregrinus Eggers
- Xyleborus pseudoangustatus Schedl
- Xyleborus pseudogracilis Schedl
- Xyleborus quercus Hopkins
- Xyleborus retrusus Schedl
- Xyleborus saxeseni (Ratzeburg)
- Xyleborus sobrinus Eichhoff
- Xyleborus subdepressus Rey
- Xyleborus subspinosus Eggers
International Common Names
- English: ambrosia beetle
- Spanish: xileboro pequeño
- French: petit xylebore
Local Common Names
- Egypt: pear root beetle
- Germany: kleine holzbohrer
- Italy: xileboro delle conifere; xileboro delle latifoglie
- Japan: sakusesu-kikuimusi
- Netherlands: kleine houtkever
- XYLBPS (Xyleborus pseudoangustatus)
- XYLBSA (Xyleborus saxeseni)
- XYLBSB (Xyleborus sobrinus)
Summary of InvasivenessTop of page X. saxesenii should be considered a high-risk quarantine pest. This is because members of the tribe Xyleborini (Xyleborinus plus related genera) are all inbreeding, with the males mating with their sisters within the parental gallery system before dispersal. Thus the introduction of only a few mated females may lead to the establishment of an active population if suitable host plants can be found and environmental conditions are satisfactory. A very wide range of host plants has been recorded for many species of Xyleborinus and related genera. Any woody material of suitable moisture content and density may be all that is required. X. saxesenii has a potentially high rate of increase due to its large brood sizes, almost all of which are females. The direct risk of establishment of populations of X. saxesenii outside its present range, followed by further spread of the species, should be considered very serious. A number of species of ambrosia beetle that normally attack only weakened host trees seem to be changing their habits and attacking healthy trees, either as exotics or in their native ranges (Kühnholz et al., 2003). Although such a change has not been noted for X. saxesenii, it would considerably increase its potential for causing economic damage to crop and forest trees.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Coleoptera
- Family: Scolytidae
- Genus: Xyleborinus
- Species: Xyleborinus saxesenii
Notes on Taxonomy and NomenclatureTop of page The species has usually been referred to in the literature as Xyleborus saxeseni. Reitter (1913) originally transferred it to the genus Xyleborinus Reitter. Holzschuh (1995) pointed out that the original spelling of the specific name used by Ratzeburg (1837) was saxesenii. The specific name librocedri used by Swaine (1934) is an error for libocedri (from the host tree Libocedrus - misspelt as Librocedrus by Swaine). Many later authors corrected the error. Wood and Bright (1992) list Xyleborus cinctipennis Schedl as a synonym. However, examination of the holotype shows that it is in fact a specimen of the related species, Xyleborinus artelineatus (RA Beaver, Chiangmai, Thailand, personal communication, 2004). The large number of synonyms is related to the widespread distribution and variability of the species. In Europe, it has sometimes been confused with Xyleborinus alni, a species imported from Eastern Asia (Holzschuh, 1995). X. alni is itself a synonym of Xyleborinus attenuatus (M Knizek, Forestry and Game Management Research Institute, Prague, Czech Republic, personal communication, 2004). In North America, prior to the 1960s (Wood, 1960; Bright, 1968), X. saxesenii was frequently confused with the unrelated species, Xyleborus xylographus. Wood and Bright (1992) list many references to this species, and additional references are given by Bright and Skidmore (1997, 2002).
DescriptionTop of page Adult
The description of the adult female is largely taken from Bright (1968). The males are much less common than the females and rarely found. They are smaller than the females, have reduced eyes, and lack wings.
Length 2.0-2.4 mm, 2.6-3.0 times longer than wide. Frons minutely reticulate, punctures distinct but faint; longitudinal line very faint, extending beyond upper level of eyes. Antennal club as long as wide. Pronotum 1.2 times longer than wide; sides parallel on posterior two-thirds, broadly rounded anteriorly; anterior slope with numerous low asperities; posterior portion minutely reticulate, punctures very fine and shallow. Scutellum conical. Elytra 1.7 times longer than wide, basal margins emarginate in scutellar area, the emargination with dense setae; strial punctures impressed, larger and more widely spaced interstrial punctures; interstriae smooth on disc, becoming uniserrately granulate toward declivity. Declivital surface dull, reticulate; interstriae one and three slightly elevated, with a row of tubercles; tubercles absent on interstriae two; apical part of interstriae nine forming lower margin of declivity, and with several acute tubercles.
Ovate, shining, pearly to yellowish white, 0.52-0.55 mm long, 0.24-0.26 mm wide.
The larva has been described in detail and figured by Lekander (1968) and May (1994). Contrary to statements in the latter paper, this is the only species of Xyleborinus of which the larva has been described. The following generic diagnosis is taken from May (1994), with additional defining characters from Lekander (1968). The larvae of the Xyleborini remain very poorly known and the description may also be applicable to species in related genera, such as Xyleborus. There are three larval instars (Hosking, 1973).
Body not expanded at thorax; abdomen with two or three dorsal folds; pronotum lacking asperities. Head free, subglobose or slightly wider than long, entire behind; frontal suture indistinct; endocarinal line long, fine; antennal cushion bearing four sensory hairs. Mandibles sharply bidentate at apex; two setae close together, arranged longitudinally. Labrum trilobate, transverse, bearing anteromedial setae of similar appearance on reflexed margin. Tormae convergent. Premental sclerite 'V'-shaped; anterior median extension obsolete. All spiracles circular, bicameral.
The pupa has been described by May (1994). Maximum length 2.0 mm. Pronotum width 0.7 mm. Cuticle glabrous. Setae pallid, short, slender, sessile. Femoral setae absent. Rostrum very short, not reaching fore coxae. Antennae disc-shaped, smooth. Pronotum having posterior margin produced medianly with a large tubercle; sides straight. Scutellum prominent. Primary pterotheca narrow, striate; secondary pterotheca longer than primary in female; absent in male (adult flightless).
DistributionTop of page
X. saxesenii is primarily a temperate zone species, although it does occur in some areas in more tropical climates. Wood and Bright (1992) include the "Samoan Islands" in the distribution of X. saxesenii. This is almost certainly an error, possibly due to confusion with the closely related species, Xyleborinus artelineatus. Wood and Bright (1992) also include New Guinea in the distribution. This may be correct, but no published records have been located. Because Nobuchi (1985) included Xyleborinus alni as a synonym of X. saxesenii, the distribution of the latter species within Japan has been kindly checked and confirmed by Dr H Goto (Forestry and Forest Products Research Institute, Tsukuba, Japan). The distribution of X. saxesenii in the area of Russia and a number of countries that were formerly part of the USSR, has been kindly checked by Dr M Yu Mandelshtam (Bolshoy Prospect 76, St Petersburg, Russia). There are unpublished records from: Georgia, Kazakhstan, Kyrgyzstan, Turkmenistan and Ukraine (M Yu Mandelshtam, Bolshoy Prospect 76, St Petersburg, Russia, personal communication, 2004). There are also unpublished records from China (Hong Kong), Namibia, New Caledonia and French Polynesia (Tahiti) (RA Beaver, Chiangmai, Thailand, personal communication, 2004), but Nobuchi's (1985) inclusion of Thailand in the distribution is an error.
Distribution TableTop of page
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.Last updated: 10 Jan 2020
History of Introduction and SpreadTop of page The species is native to the Palearctic region, but has been widely introduced probably through commerce. It is not known whether it is native or introduced in the Atlantic islands of the Azores, Canary Islands and Madeira. If introduced, this probably took place several hundred years ago. The date of introduction to North America is not known (Mattson et al., 1994), but was probably at least 200 years ago. Its present distribution in North America suggests that it was introduced separately to East and West coasts, and has since spread towards the interior of the continent. In Hawai'i, it was well established on the islands of Hawai'i and Maui before 1885, when Blackburn described it as Xyleborus frigidus (Samuelson, 1981). In South America, the first record from Argentina is in 1920 (Schedl, 1938), from Brazil prior to 1937 (Schedl, 1937), and from Chile in 1962 (Schedl, 1966). In South Africa, the first record is from 1925 in Cape Province (Schedl, 1963). It had spread to Natal and Transvaal, and was causing damage to pine plantations by the 1950s (Schedl, 1963). In Australia, it was present in Queensland in 1936, in New South Wales in 1945 (Schedl, 1949), and in Western Australia in 1954 (Schedl, 1962). In New Zealand, the species was probably introduced in the battens used to close cable drums imported from England, in about 1957 (Milligan, 1969). It was first recognised as an established exotic species in 1963 (Milligan, 1969; Brockerhoff and Bain, 2000).
Risk of IntroductionTop of page A number of species of Xyleborus and related genera with similar habits to X. saxesenii have become important pests of tree crops, ornamental and native trees in tropical, subtropical and warm temperate zone areas where they have been introduced. The risk of introduction for X. saxesenii must be considered high. Once established, such species are difficult to eradicate, and are likely to spread with the movement of infested plants, as well as by normal dispersal of the adults. The species has been introduced to new areas, primarily, but not entirely, in temperate and subtropical regions, and has spread within these areas, over at least the last 200 years. Further spread is likely.
HabitatTop of page The species occurs equally in managed and unmanaged environments, although it tends to be more abundant in the former, because suitable host material is usually more abundant in such environments than in natural forests. Where it has been introduced, it may become more abundant than the native species (Mudge et al., 2001; Oliver and Mannion, 2001).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Protected agriculture (e.g. glasshouse production)||Present, no further details||Harmful (pest or invasive)|
|Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Present, no further details||Harmful (pest or invasive)|
|Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Riverbanks||Present, no further details||Harmful (pest or invasive)|
|Wetlands||Present, no further details||Harmful (pest or invasive)|
|Deserts||Present, no further details||Harmful (pest or invasive)|
|Coastal areas||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page Like the great majority of ambrosia beetles, X. saxesenii is polyphagous, attacking almost any host tree of suitable size, and in a suitable condition for the associated ambrosia fungus to grow. Bright (1968) notes that nearly all genera of deciduous trees in the USA and southern Canada can be attacked, as well as coniferous genera. Wood and Bright (1992) list 27 genera, and Bright and Skidmore (1997) add a further 12 genera. Hosking (1979) notes that more than 30 species of native and introduced trees are attacked in New Zealand. The list of hosts in this datasheet is a selection only, and it can be expected that where a genus is listed, all species of that genus will be attacked, and not just those listed. It is not possible to distinguish between main hosts and other hosts. Similarly the distinction between wild and cultivated hosts is artificial, because many trees occur both in the wild and in plantations.
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page Flowering stage, Fruiting stage, Post-harvest, Vegetative growing stage
List of Symptoms/SignsTop of page
|Leaves / yellowed or dead|
|Leaves / yellowed or dead|
|Stems / gummosis or resinosis|
|Stems / gummosis or resinosis|
|Stems / internal discoloration|
|Stems / internal discoloration|
|Stems / internal feeding|
|Stems / internal feeding|
|Stems / lodging; broken stems|
|Stems / lodging; broken stems|
|Stems / mycelium present|
|Stems / mycelium present|
|Stems / visible frass|
|Stems / visible frass|
|Whole plant / early senescence|
|Whole plant / early senescence|
|Whole plant / frass visible|
|Whole plant / frass visible|
|Whole plant / internal feeding|
|Whole plant / internal feeding|
|Whole plant / wilt|
|Whole plant / wilt|
Biology and EcologyTop of page The important pest species in the genus Xyleborus and the related genera Xylosandrus, Xyleborinus and Euwallacea are all ambrosia beetles in the Xyleborini, a tribe with a social organization of extreme polygamy. The sexual dimorphism is strongly developed, and the ratio of females to males is high. Some species infest small twigs and shoots, others are found in larger branches and poles, and others are found in large timber; others may breed in material of almost any size. In general, most species bore through the bark and into the wood where an enlarged chamber and/or branching tunnels of varying size and shape are constructed. The tunnels into the wood are highly variable in depth and shape, depending on the species involved in the construction. All species are closely associated in a mutualistic relationship with ambrosia fungi, which grow on the walls of the gallery system and in the surrounding wood, and on which both adults and larvae feed (Beaver, 1989).
Fischer (1954) in Europe, and Hosking (1973) in New Zealand made detailed studies of the biology of X. saxesenii. In Central Europe and in North America (Missouri), the flight period of X. saxesenii begins at the end of April and beginning of May (Fischer, 1954; Roling and Kearby, 1975). The peak of flight activity is in the afternoon, and is related to temperature (Hosking, 1973). The females have already mated with their brother(s) in the maternal gallery system, and disperse to find new breeding sites. The females are attracted to ethanol (Roling and Kearby, 1975; Klimetzek et al., 1986; Lombardero, 1996; Markalas and Kalapanida, 1997; Oliver and Mannion, 2001), a volatile chemical which is released by decaying wood, and which serves as a good indicator of suitable breeding material. Other volatiles may also be involved (Flechtmann et al., 1999). The initial positively phototropic response of the beetles is reversed following flight exercise (Hosking, 1973).
The female bores a radial entry tunnel directly into the wood. This may penetrate 4 cm or more, or may curve at some point to follow a growth ring (Hosking, 1973). It may (Fischer, 1954) or may not (Hosking, 1973) branch. Oviposition begins once the ambrosia fungus has begun to grow on the walls of the gallery, and extends over two (Fischer, 1954) to twelve (Hosking, 1973) weeks. The eggs are laid in loose clumps of up to 8-12. The young larvae enlarge the maternal gallery to form an irregular brood chamber in the vertical plane, extending above and/or below the maternal gallery. As gallery development continues, lateral chambers extending vertically along the growth rings may be excavated (Hosking, 1973). The final form of the gallery system is variable, but the vertical chambers are quite distinct from the branching system of tunnels that have not been enlarged, found in many species of Xyleborus.
Pupation occurs in the gallery chambers. Contrary to Fischer (1954), the teneral adults do not take part in further extensions of the gallery (Hosking, 1973). The development period from larva to adult is 7 to 15 weeks (Fischer, 1954). The number of males per female is very variable. Fischer (1954) gives an average value of 1:20. In New Zealand, the ratio varied from 1:4 to 1:64 in different years, and there is similar variation between individual gallery systems, with some galleries having no male (Hosking, 1973). The males mate with their sisters within the gallery system. The males are unable to fly, and usually die within the parental gallery, but some emerge from the gallery and can be found crawling over the bark (Furniss and Johnson, 1987). It is not known whether these males can successfully enter other gallery systems and mate with the females there. Total brood size appears to be larger than in many xyleborines, with occasional galleries approaching or exceeding 100 individuals (Milligan, 1969; Egger, 1973; Hosking, 1973). Unpublished studies by K Peer and M Taborsky (Institute of Zoology, University of Berne, Switzerland, personal communication, 2004) show that up to 50% of all females never disperse, but remain in the parental gallery. They do not reproduce there, but apparently help to raise their sisters, thus increasing colony productivity, and suggesting a primitively eusocial life.
The number of generations per year is related to temperature. In Central Europe, there are one or two generations, but breeding is likely to be continuous in warmer climates, with all stages of development present at any time of year.
In the majority of ambrosia beetles, the ambrosia fungus is transported by the dispersing female, in special cuticular pockets or mycangia. These are present in X. saxesenii in the base of the elytra (Francke-Grosmann, 1956), but the ambrosia fungus, Ambrosiella sulphurea (Batra, 1967), is apparently transmitted endozoically in the form of micromycelia in the gut (Francke-Grosmann, 1975).
In its attacks on fruit trees, X. saxesenii is often associated with another ambrosia beetle, Xyleborus dispar, with similar habits, but a tendency to more primary attacks (Fischer, 1954).
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
Notes on Natural EnemiesTop of page Compared with bark beetles, the immature stages of xyleborine ambrosia beetles have few natural enemies. The female parent normally remains in the gallery entrance whilst the immature stages are developing, preventing the entry of potential predators and parasitoids. Provided the female remains alive and the growth of the ambrosia fungus on which the larvae feed is satisfactory, mortality of the immature stages is likely to be very low. Most mortality is probably during the dispersal of the adults, and during gallery establishment. Lizards, clerid beetles and ants are predators of adult ambrosia beetles as they attempt to bore into the host tree. The adults will also fail to oviposit if the ambrosia fungus fails to establish in the gallery.
Three species of parasitoid Hymenoptera have been recorded from X. saxesenii (Fischer, 1954; Noyes, 2003), but none seems likely to be an important cause of mortality of the immature stages. Perniphora robusta is a pteromalid that attacks ambrosia beetles (Trypodendron spp., Xyleborus spp.) throughout Europe (Balazy, 1963; Capecki, 1963; Hedqvist, 1963). Its larvae feed externally on the beetle larvae (Eichhorn and Graf, 1974). Eurytoma polygraphi is better known in Europe by its synonym, Ipideurytoma spessivtsevi [Eurytoma spessivtsevi] (Noyes, 2003). It can parasitise X. saxesenii directly, but is also known as a hyperparasite of Perniphora robusta (Novak, 1960). The braconid Blacus fuscipes, noted by Fischer (1954), should be considered dubious. The biology of Blacinae is poorly known, but the species appear to be solitary endoparasitoids of coleopteran larvae (Shaw and Huddleston, 1991). A few species are known to parasitize bark beetles (Hedqvist, 1998). The record of Pteromalus bimaculatus (Fischer, 1954), which is a synonym of Cheiropachus colon [Cheiropachus quadrum], a parasite of bark beetles not ambrosia beetles, is unlikely to be a natural enemy of X. saxesenii.
The most important coleopteran predators of X. saxesenii in Europe and North America are likely to be clerid beetles in the genera Thanasimus and Enoclerus. The adults are voracious predators of adult scolytids, and the larvae predate the immature stages (Opitz, 2002). The colydiid beetles, Colydium elongatum and Colydium lineola are recorded as predators by Fischer (1954) and Hubbard (1897) respectively, and the trogossitid, Nemosoma elongatum by Fischer (1954). All three species are generalist predators on bark beetles and other insects below bark and in wood, and are unlikely to have an important impact on X. saxesenii populations.
Unidentified nematodes have been noted in the body cavity of both adults and larvae (Fischer, 1954). Their effect on the populations of X. saxesenii is unknown.
Means of Movement and DispersalTop of page Natural Dispersal
The adult females fly readily and flight is one of the main means of movement and dispersal to previously uninfected areas. However, the movement of infested woody material in timber, ship dunnage and crating is more important. Numerous species of Xyleborus and related genera have been taken from raw logs destined for sawmills, discarded ship dunnage, and in similar circumstances in port cities.
In addition to the principal ambrosia fungus, Ambrosiella sulphurea, the dispersing female of X. saxesenii also transports the spores of other fungi (Francke-Grosmann, 1975). The spores may either be carried in the mycetangia or externally on the cuticle. The fungi include species of Ceratocystis, Trichoderma and Penicillium (Francke-Grosmann, 1975). Ambrosiella species are not pathogenic, although they do cause staining of the wood around the gallery systems. However, some Ceratocystis species are well-known pathogens of the host tree. It is clearly possible for X. saxesenii to transmit pathogenic fungi and bacteria. The species has been implicated in the transmission of the pathogenic bacterium Pseudomonas avellanae, between hazelnut trees in Italy (Scortichini, 1998).
Movement in Trade
The species has frequently been intercepted in imported timber and other woody material (e.g. Ohno, 1991; Brockerhoff et al., 2003)
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||adults||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; larvae; pupae||Yes||Pest or symptoms not visible to the naked eye but usually visible under light microscope|
|Wood||adults; eggs; larvae; pupae||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)|
|Growing medium accompanying plants|
|True seeds (inc. grain)|
Wood PackagingTop of page
|Wood Packaging liable to carry the pest in trade/transport||Timber type||Used as packing|
|Loose wood packing material||Fresh, unseasoned wood||Yes|
|Solid wood packing material with bark||Fresh, unseasoned wood||Yes|
|Solid wood packing material without bark||Fresh, unseasoned wood||Yes|
|Wood Packaging not known to carry the pest in trade/transport|
|Processed or treated wood|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
|Fisheries / aquaculture||None|
ImpactTop of page In most parts of Europe and North America, X. saxesenii has no major economic importance, although it is often involved, together with Xyleborus dispar, in attacks on the trunks and branches of fruit trees (Malus, Prunus, Pyrus) (e.g. Fischer, 1954; Egger, 1973; Lombardero, 1996). In Egypt, it attacks the roots of fruit trees, especially plum and pear, but not citrus, causing damage (Batt, 2000). It is one of several xyleborine species involved in attacks on young Chinese chestnut trees (Castanea mollissima) in Tennessee, USA (Oliver and Mannion, 2001). In South Africa, following fire in pine plantations, the species attacked moribund trees, and also invaded timber yards attacking many different species (Schedl, 1963). In New Zealand, the species is commonly found in freshly sawn timber and logs. Its attacks are important because timber containing live insects may not be exported. Due to the growing volume of timber exports involved, the economic consequences may be "considerable" (Milligan, 1969). Affected logs have to be diverted to local use, or expensively treated to kill the insects (Hosking, 1979).
Economic ImpactTop of page In most parts of Europe and North America, X. saxesenii has no major economic importance, although it is often involved, together with Xyleborus dispar, in attacks on the trunks and branches of fruit trees (Malus, Prunus, Pyrus) (e.g. Fischer, 1954; Egger, 1973; Lombardero, 1996). In Egypt, it attacks the roots of fruit trees, especially plum and pear, but not citrus, causing damage (Batt, 2000). It is one of several xyleborine species involved in attacks on young Chinese chestnut trees (Castanea mollissima) in Tennessee, USA (Oliver and Mannion, 2001). In South Africa, following fire in pine plantations, the species attacked moribund trees, and also invaded timber yards attacking many different species (Schedl, 1963). In New Zealand, the species is commonly found in freshly sawn timber and logs. Its attacks are important because timber containing live insects may not be exported. Due to the growing volume of timber exports involved, the economic consequences may be "considerable" (Milligan, 1969). Affected logs have to be diverted to local use, or expensively treated to kill the insects (Hosking, 1979).
Impact: BiodiversityTop of page In parts of the USA, it has been noted that X. saxesenii can be more abundant than native species of Scolytidae (Mudge et al., 2001; Oliver and Mannion, 2001). However, it is not clear whether it has significantly reduced their abundance, or is occupying host material that would otherwise not have been exploited.
Detection and InspectionTop of page X. saxesenii can be detected by using traps baited with ethanol placed in orchards, plantations and similar places where infestations are suspected, and around ports or other facilities where potentially infested material may be stored. Mani et al. (1986, 1990), Bambara et al. (2002) and Grégoire et al. (2003) describe simple types of traps. Oliver and Mannion (2001) describe the use of funnel traps with ethanol lures. Flight barrier traps or window traps baited with ethanol have also been used (e.g. Roling and Kearby, 1975; Klimetzek et al., 1986; Weber and McPherson, 1991; Simon, 1995; Markalas and Kalapanida, 1997). Visual inspection of suspected infested material is required to detect the presence of ambrosia beetles. Infestations are most easily detected by the presence of entry holes made by the attacking beetles, and the presence of frass produced during gallery construction. The ambrosia beetle species involved can usually only be determined by dissection of the breeding material.
Similarities to Other Species/ConditionsTop of page Species of Xyleborinus can be distinguished from related xyleborine genera (Ambrosiodmus, Euwallacea, Xyleborus, Xylosandrus), which may occur in the same host tree, by the conical scutellum which lies between the recurved bases of the elytra. In Europe, X. saxesenii can be distinguished from Xyleborinus alni by its smaller size (2.0-2.4 mm versus 2.5-2.8 mm), and the smaller, less pointed tubercles on interstriae one and three (Holzschuh, 1995). In the USA (apart from Florida) and Canada, and in New Zealand, X. saxesenii is the only species in the genus that is likely to occur. It is not possible here to give distinguishing characters from other Xyleborinus species that may co-occur with X. saxesenii in other countries where the species has been introduced. Keys to Palearctic species of Xyleborini, including X. saxesenii, can be found in Balachowsky (1949), Schedl (1981), and Pfeffer (1995). Bright (1968), Wood (1982), Atkinson et al. (1990) and Vandenberg et al. (2000) include keys to Nearctic species.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
X. saxesenii is a secondary species attacking trees that are stressed or unhealthy. For this reason, measures to improve the health of trees are very important. Where only a few branches are attacked, they should be cut out and burned, and the resulting wound on the tree sealed with pitch or mastic to prevent the entry of pathogenic fungi and bacteria (Egger, 1973; Scortichini, 1998). It is essential to do this before the new generation of beetles emerges. Care should be taken to avoid damaging the lower trunk during cultivation (Scortichini, 1998).
When attacks occur on logs, whether in the forest or in stockpiles, the affected timber should be rapidly removed and treated to prevent the emergence of a new generation of beetles. Drying prevents the growth of the fungus, and hence the development of the beetle.
No method of biological control of X. saxesenii exists at present. The natural enemies mentioned in this datasheet (see Natural Enemies) do not provide effective control, and augmentation is not likely to produce much improvement.
Chemical control of X. saxesenii is difficult and expensive due to its protected breeding sites within the tree. Therefore, sprays are only applied in exceptional cases. Compounds used previously are now banned from use. Compounds registered at present, such as carbaryl, organophosphates and pyrethroids are likely to only give partial control if the beetles have already penetrated far into the tree. Insecticides are applied when the insects start flying and searching for suitable host plants (maximum temperature 18-20°C; first catches in alcohol traps) or at the latest, when the first beetles start boring entrance holes. The concentration of the insecticide is often higher than usual and the whole tree, especially the trunk and larger branches, should be sprayed thoroughly. When trap catches continue to be significant, the application has to be repeated after 2 to 3 weeks. The suggestion by Fischer (1954) that a pad of cotton wool soaked in carbon disulphide should be applied to the entrance hole to kill the parent adult, is not of any real practical value because of the difficulty in locating the individual galleries in large trees.
For detecting and monitoring the presence of X. saxesenii, alcohol-baited traps can be used in orchards, or around sawmills or log stockpiles, and in similar situations (see Detection and Inspection Methods). If sufficient traps are used, some control of the beetle may be possible.
Integrated Pest Management
Control of X. saxesenii must rely on a combination of different methods. All measures promoting plant health are essential. Attacked plant parts must be removed in time. In orchards or other areas with a risk of damage, alcohol traps should be placed for monitoring or for control. Only in exceptional cases do insecticide sprays become necessary. Eventually, it may be possible to develop the use of non-host volatiles as repellents to prevent, or at least reduce, attacks (Borden et al., 2003).
ReferencesTop of page
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