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Datasheet

Xylosandrus crassiusculus
(Asian ambrosia beetle)

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Datasheet

Xylosandrus crassiusculus (Asian ambrosia beetle)

Summary

  • Last modified
  • 16 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Preferred Scientific Name
  • Xylosandrus crassiusculus
  • Preferred Common Name
  • Asian ambrosia beetle
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Uniramia
  •         Class: Insecta
  • Summary of Invasiveness
  • X. crassiusculus should be considered a high-risk quarantine pest; most of the species in Xyleborus and related genera should be considered potential quarantine pests. This reflects the fact that since members of the tribe Xyleborini (Xyleborus plus...

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Pictures

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PictureTitleCaptionCopyright
Xylosandrus crassiusculus (Asian ambrosia beetle); lateral view. USA. VA. Albemarle Co., Charlottesville, 20 May 2005, from funnel trap; det. R.J. Rabaglia, 2007.
TitleAdult
CaptionXylosandrus crassiusculus (Asian ambrosia beetle); lateral view. USA. VA. Albemarle Co., Charlottesville, 20 May 2005, from funnel trap; det. R.J. Rabaglia, 2007.
Copyright©Pest & Diseases Image Library (PaDIL)/Bugwood.org - CC BY 3.0 AU
Xylosandrus crassiusculus (Asian ambrosia beetle); lateral view. USA. VA. Albemarle Co., Charlottesville, 20 May 2005, from funnel trap; det. R.J. Rabaglia, 2007.
AdultXylosandrus crassiusculus (Asian ambrosia beetle); lateral view. USA. VA. Albemarle Co., Charlottesville, 20 May 2005, from funnel trap; det. R.J. Rabaglia, 2007.©Pest & Diseases Image Library (PaDIL)/Bugwood.org - CC BY 3.0 AU

Identity

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Preferred Scientific Name

  • Xylosandrus crassiusculus (Motschulsky)

Preferred Common Name

  • Asian ambrosia beetle

Other Scientific Names

  • Dryocoetes bengalensis Stebbing
  • Xyleborus bengalensis Stebbing
  • Xyleborus crassiusculus (Motschulsky)
  • Xyleborus declivigranulatus Schedl
  • Xyleborus ebriosus Niisima
  • Xyleborus mascarenus Hagedorn
  • Xyleborus okoumeensis Schedl
  • Xyleborus semigranosus Blandford
  • Xyleborus semiopacus Eichhoff
  • Xylosandrus semigranosus (Blandford)
  • Xylosandrus semiopacus (Eichhoff)

International Common Names

  • English: granulate ambrosia beetle

EPPO code

  • XYLBCR (Xyleborus crassiusculus)
  • XYLBEB (Xyleborus ebriosus)

Summary of Invasiveness

Top of page X. crassiusculus should be considered a high-risk quarantine pest; most of the species in Xyleborus and related genera should be considered potential quarantine pests. This reflects the fact that since members of the tribe Xyleborini (Xyleborus plus related genera) are all parthenogenetic, the introduction of only a few individuals (females) may lead to the establishment of an active population if suitable host plants can be found and environmental conditions are satisfactory. Even suitable host plants may not be a limiting factor since the adult beetle does not actually feed on the plant material but uses it as a medium for growing the fungus which is the larval food. Any woody material of suitable moisture content and density may be all that is required. A very wide range of host plants have been recorded for many species of Xyleborus and related genera. The direct risk of establishment of populations of species of Xyleborus into tropical and sub-tropical areas should be considered extremely serious.

Taxonomic Tree

Top of page
  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Uniramia
  •                 Class: Insecta
  •                     Order: Coleoptera
  •                         Family: Scolytidae
  •                             Genus: Xylosandrus
  •                                 Species: Xylosandrus crassiusculus

Notes on Taxonomy and Nomenclature

Top of page Many species previously classified in the genus Xyleborus have now been transferred into other genera such as Ambrosiodmus, Euwallacea, Xylosandrus and Xyleborinus, including X. crassiusculus. These species are all ambrosia beetles. A number of species within the Xyleborini, the tribe in which Xyleborus and related genera are placed, can be considered potential pests to agriculture and forestry; X. crassiusculus is one of the more important species.

Description

Top of page Adult Female

Length 2.2-2.5 mm. Frons weakly convex, with a distinct median line, surface coarsely granulate, sparsely punctate. Antennal club solid on posterior face, no sutures present. Pronotum about as long as wide; sides weakly arcuate, anterior margin narrowly rounded, with 8 or 9 weak serrations. Elytra 1.2-1.3 times longer than wide, apex broadly rounded. Elytral declivity abrupt, convex, surface opaque with dense, confused granules and rows of long stout setae.

Immature Stages

The egg and pupa have not been described. The larvae of X. crassiusculus and Xylosandrus discolor are briefly described and keyed by Gardner (1934). Gardner (1934) describes the mature larva (as Xyleborus semigranosus) as follows: length about 3.5 mm. Head pale, slightly wider than long. Labrum with strong posterior extension. Epipharyngeal setae very small. Maxillary palp with apical segment only slightly longer than wide. Labial palps separated by about width of a basal segment, apical segment globular, not longer than wide. Abdominal terga with two distinct folds separated by an extremely narrow subdivision. Spiracles with combined width of air-tubes equal to diameter of atrium. Skin rather densely covered with micro-asperities.

Too little is known of the larvae of other species of Xylosandrus to be sure whether the description is adequate to separate X. crassiusculus larvae from those of related species. Gardner (1934) distinguishes the species from Xylosandrus discolor by the micro-asperate (versus smooth) skin.

Distribution

Top of page There are unpublished records from Brunei Darussalam, Christmas Island (Indian Ocean), Reunion, South Africa (RA Beaver, Chiangmai, Thailand, personal communication, 2004). Browne (1968) reported this species from Fiji, however, this record is incorrect and this species has not yet been recorded from the Fiji islands.

Distribution Table

Top 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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

BhutanPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
ChinaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-FujianPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Hong KongPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-HunanPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-SichuanPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-TibetPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-YunnanPresentNative Not invasive Yin et al., 1984; CABI/EPPO, 2009; EPPO, 2018
IndiaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Andaman and Nicobar IslandsPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-AssamPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Himachal PradeshPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-KarnatakaPresentNative Not invasive Sreedharan et al., 1991; CABI/EPPO, 2009; EPPO, 2018
-KeralaPresentCABI/EPPO, 2009; EPPO, 2018
-Madhya PradeshPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-MaharashtraPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Tamil NaduPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Uttar PradeshPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-West BengalPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
IndonesiaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Irian JayaPresentNative Not invasive Schedl, 1940; CABI/EPPO, 2009; EPPO, 2018
-JavaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-KalimantanPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-MoluccasPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Nusa TenggaraPresentEPPO, 2018
-SulawesiPresentNative Not invasive Kalshoven, 1959; CABI/EPPO, 2009; EPPO, 2018
-SumatraPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
JapanPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Bonin IslandPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009
-HokkaidoPresentNative Not invasive Murayama, 1953; CABI/EPPO, 2009; EPPO, 2018
-HonshuPresentNative Not invasive Murayama, 1953; CABI/EPPO, 2009; EPPO, 2018
-KyushuPresentNative Not invasive Murayama, 1953; CABI/EPPO, 2009; EPPO, 2018
-ShikokuPresentNative Not invasive Murayama, 1953; CABI/EPPO, 2009; EPPO, 2018
Korea, DPRPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Korea, Republic ofPresentNative Not invasive Murayama, 1931; Choo et al., 1983; CABI/EPPO, 2009; EPPO, 2018
MalaysiaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-Peninsular MalaysiaPresentNative Not invasive Browne, 1961; CABI/EPPO, 2009; EPPO, 2018
-SabahPresentNative Not invasive Chey VunKhen, 2002; CABI/EPPO, 2009; EPPO, 2018
-SarawakPresentNative Not invasive Schedl, 1964; CABI/EPPO, 2009; EPPO, 2018
MyanmarPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
NepalPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
PakistanPresentKhuhro et al., 2005; CABI/EPPO, 2009; EPPO, 2018
PhilippinesPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Sri LankaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
TaiwanPresentNative Not invasive Murayama, 1934; Eggers, 1939; CABI/EPPO, 2009; EPPO, 2018
ThailandPresentNative Not invasive Beaver and Browne, 1975; CABI/EPPO, 2009; EPPO, 2018
VietnamPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018

Africa

CameroonPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Congo Democratic RepublicPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Côte d'IvoirePresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Equatorial GuineaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
GabonPresentEPPO, 2018
GhanaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
KenyaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
MadagascarPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
MauritaniaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
MauritiusPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
NigeriaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
SeychellesPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Sierra LeonePresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
TanzaniaPresentIntroduced Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018

North America

USAPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-AlabamaPresentHorn and Horn, 2006; CABI/EPPO, 2009; EPPO, 2018
-ArkansasPresentCABI/EPPO, 2009; EPPO, 2018
-DelawarePresentRabaglia and Valenti, 2003; CABI/EPPO, 2009; EPPO, 2018
-FloridaPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-GeorgiaPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-HawaiiPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-IndianaPresentIntroduced Invasive Pierce et al., 2005; CABI/EPPO, 2009; EPPO, 2018
-KansasPresentEPPO, 2018
-LouisianaPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-MarylandPresentIntroduced Invasive Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-MichiganPresentCABI/EPPO, 2009; EPPO, 2018
-MississippiPresentIntroduced Invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
-MissouriPresentCABI/EPPO, 2009; EPPO, 2018
-NebraskaPresentCABI/EPPO, 2009; EPPO, 2018
-New JerseyPresentCABI/EPPO, 2009; EPPO, 2018
-New YorkPresentCABI/EPPO, 2009; EPPO, 2018
-North CarolinaPresentIntroduced Invasive Wood and Bright, 1992; Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-OhioPresentIntroducedLightle et al., 2007; CABI/EPPO, 2009; EPPO, 2018
-OklahomaPresentIntroduced Invasive Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-OregonPresentIntroducedLaBonte et al., 2005; CABI/EPPO, 2009; EPPO, 2018
-South CarolinaPresentIntroduced Invasive Wood and Bright, 1992; Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-TennesseePresentIntroduced Invasive Oliver and Mannion, 2001; Bright and Skidmore, 2002; CABI/EPPO, 2009; EPPO, 2018
-TexasPresentIntroduced Invasive Wood and Bright, 1992; Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-VirginiaPresentIntroduced Invasive Bambara and Casey, 2003; CABI/EPPO, 2009; EPPO, 2018
-WashingtonPresentIntroducedLaBonte et al., 2005; CABI/EPPO, 2009; EPPO, 2018

Central America and Caribbean

Costa RicaPresentCABI/EPPO, 2009; EPPO, 2018
GuatemalaRestricted distributionEPPO, 2018
PanamaPresentCABI/EPPO, 2009; EPPO, 2018

South America

French GuianaRestricted distributionEPPO, 2018

Europe

BelgiumAbsent, no pest recordEPPO, 2018
FranceRestricted distributionEPPO, 2018
ItalyPresentIntroducedPennacchio et al., 2003; CABI/EPPO, 2009; EPPO, 2018
-Italy (mainland)PresentCABI/EPPO, 2009
LithuaniaAbsent, confirmed by surveyEPPO, 2018
SloveniaTransient: actionable, under eradicationEPPO, 2018
SpainRestricted distributionEPPO, 2018

Oceania

AustraliaPresentPresent based on regional distribution.
-QueenslandRestricted distributionIPPC, 2017
New CaledoniaPresentIntroducedWood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
New ZealandAbsent, intercepted onlyIntroducedBrockerhoff et al., 2003; CABI/EPPO, 2009; EPPO, 2018
PalauPresentIntroducedWood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
Papua New GuineaPresentNative Not invasive Wood and Bright, 1992; CABI/EPPO, 2009; EPPO, 2018
SamoaPresentIntroduced Invasive Beeson, 1929; Beaver, 1976; CABI/EPPO, 2009; EPPO, 2018

History of Introduction and Spread

Top of page X. crassiusculus was probably introduced to the Afrotropical region from the Oriental region hundreds of years ago by early traders. It has become one of the commonest ambrosia beetles in the rain forest (Schedl, 1963) in both East and West Africa. In North America, it was first discovered near Charleston, South Carolina in 1974 (Anderson, 1974). From there it spread to North Carolina (Hunt, 1979), Louisiana and Florida (Chapin and Oliver, 1986; Deyrup and Atkinson, 1987), and to Mississippi and Texas (Atkinson et al., 1991). Most recently, it has been reported from Tennessee (Oliver and Mannion, 2001). The species is now well-established in south-eastern USA, and may be expected to spread further where climatic conditions are suitable. X.crassiusculus was intercepted in Canada in 1997, but has not established there (Krcmar-Nozic et al., 2000). It seems likely that climatic conditions are too harsh there for the species. In the Hawaiian islands, the species was first found on Hawaii in 1950, and became established on most of the windward islands during the 1950s (Samuelson, 1981). There is no information on when it was introduced to other Pacific Islands. In all cases, the introduction has been accidental.

Risk of Introduction

Top of page Two other species of Xylosandrus, Xylosandrus compactus and Xylosandrus morigerus, with similar habits to X. crassiusculus, have become important pests of tree crops, ornamental and native trees in tropical and subtropical areas where they have been introduced. The risk of introduction for X. crassiusculus must be considered high, most probably in the twigs and small branches of imported plants, although, because it can also breed in fresh timber, other pathways are also possible. 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. X. crassiusculus is listed as a quarantine pest in New Zealand, but apparently not elsewhere. This should be remedied.

Hosts/Species Affected

Top of page Members of Xyleborus and the related genera Ambrosiodmus, Euwallacea, Xyleborinus and Xylosandrus are all ambrosia beetles that feed and breed in a variety of forest trees and shrubs. Depending on the species, they may be found in small branches and seedlings to large logs. All are potentially damaging to agriculture and/or forestry under suitable conditions. Many species, previously considered of only minor importance, may become important pests in agriculture and forestry as a result of the continuing destruction of natural forests and the expansion of forest and tree crop plantations, agroforestry and agriculture.

X. crassiusculus occurs in a very wide variety of host plants (e.g. Kalshoven, 1959; Browne, 1961; Schedl, 1963; Beaver, 1976; Samuelson, 1981). Schedl (1963) lists 94 species in 28 families in Africa, and 63 species in 34 families outside Africa, and many more species have since been added to this list (Wood and Bright, 1992). It is evident that almost any broad-leaved tree or sapling can be attacked, although the species has not been recorded from conifers. It is particularly important as a pest of crop and ornamental trees. Its attacks are sometimes primary on apparently healthy hosts. It has been recorded killing saplings of forest trees shortly after transplanting. Given the great range of host trees attacked, and the differences between geographical areas, it is not possible to distinguish 'main host' trees from 'other host' trees (see List of hosts). It may be expected that almost any non-coniferous crop, plantation or ornamental tree in a particular area can be attacked. The Host list in this datasheet contains a selection of hosts only.


Host Plants and Other Plants Affected

Top of page
Plant nameFamilyContext
Acacia koa (koa)FabaceaeWild host
Acacia mangium (brown salwood)FabaceaeOther
AlbiziaFabaceaeOther
Albizia lebbeck (Indian siris)FabaceaeOther
Artocarpus integer (champedak)MoraceaeOther
Asimina triloba (Pawpaw-apple)AnnonaceaeOther
Aucoumea klaineana (okoume)BurseraceaeOther
Bauhinia albaFabaceaeOther
CalamusArecaceaeOther
Carya illinoinensis (pecan)JuglandaceaeOther
Castanea mollissima (hairy chestnut)FagaceaeOther
Ceiba pentandra (kapok)BombacaceaeOther
Cercis canadensis (eastern redbud)FabaceaeOther
CinchonaRubiaceaeOther
Cinnamomum camphora (camphor laurel)LauraceaeOther
Cinnamomum verum (cinnamon)LauraceaeOther
Coffea (coffee)RubiaceaeOther
Dalbergia sissooFabaceaeOther
Deckenia nobilisArecaceaeWild host
Delonix regia (flamboyant)FabaceaeOther
Diospyros kaki (persimmon)EbenaceaeOther
Elaeis guineensis (African oil palm)ArecaceaeOther
Eucalyptus camaldulensis (red gum)MyrtaceaeOther
Eucalyptus robusta (swamp mahogany)MyrtaceaeOther
Ficus racemosa (cluster tree)MoraceaeOther
Grevillea robusta (silky oak)ProteaceaeOther
Hevea brasiliensis (rubber)EuphorbiaceaeOther
Khaya ivorensis (African mahogany)MeliaceaeOther
LaburnumFabaceaeOther
Leucaena leucocephala (leucaena)FabaceaeOther
Liquidambar styraciflua (Sweet gum)HamamelidaceaeOther
Litchi sinensisSapindaceaeOther
Macadamia ternifolia (Queensland nut)ProteaceaeOther
MagnoliaMagnoliaceaeOther
Mangifera indica (mango)AnacardiaceaeOther
Metrosideros collinaMyrtaceaeWild host
Milicia excelsa (African teak)MoraceaeOther
Mimosa (sensitive plants)FabaceaeOther
Persea americana (avocado)LauraceaeOther
Prunus (stone fruit)RosaceaeOther
Prunus persica (peach)RosaceaeOther
Saccharum officinarum (sugarcane)PoaceaeOther
ShoreaDipterocarpaceaeWild host
Syzygium cumini (black plum)MyrtaceaeOther
Tectona grandis (teak)LamiaceaeOther
Theobroma cacao (cocoa)SterculiaceaeOther
Toona ciliata (toon)MeliaceaeOther
Ulmus (elms)UlmaceaeWild host

Growth Stages

Top of page Flowering stage, Fruiting stage, Post-harvest, Seedling stage, Vegetative growing stage

Symptoms

Top of page Attacked plants may show signs of wilting, branch die-back, shoot breakage, chronic debilitation, sun-scorch or a general decline in vigour.

List of Symptoms/Signs

Top of page
SignLife StagesType
Growing point / dieback
Stems / lodging; broken stems
Whole plant / wilt

Biology and Ecology

Top 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, while 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 of varying size and shape is constructed. The tunnels into the wood are highly variable in depth and shape, depending on the species involved in the construction. Generally only unhealthy or newly fallen material is infested, but some species are capable of attacking host plants following only a slight set-back, for example, transplanting or temporarily unfavourable conditions such as drought or mechanical injury. A few species have become aggressive under certain conditions, and have thereby attained the status of important pests.

All species of Xyleborus and the related genera are closely associated with ambrosial fungi. Some of these fungi are phytopathogenic and all species of Xyleborus and related genera should be considered to be possible vectors of plant disease.

Some details of the biology of X. crassiusculus are given by Beeson (1930), Browne (1961), Schedl (1963) and Beaver (1976, 1988). The species is known to prefer fresh, moist wood (Beeson, 1930; Beaver, 1988), and attack-densities are usually higher on wood in the shade than in the sun, and higher on the lower side of logs. Stems of fairly small diameter (2.5 - 8 cm) are usually attacked, but sometimes larger logs. The gallery sytem is somewhat variable depending on the size of the stem. In large stems, it branches several times in one transverse plane, and may penetrate 5 cm or more. In small stems, there are fewer branches and one or more may extend along the axis of the stem. In the palm rachis, the galleries run more irregularly through the fibrous tissues. Brood sizes up to 65 have been recorded in the Congo, and up to 100 in Ghana (Schedl, 1963), but usually range between about 10 and 40 (Beaver, 1988). In the tropics, breeding is continuous throughout the year, with overlapping generations, so that the species is present at all times and in all stages of development (Browne, 1968). In south-eastern USA, beetles are active from the beginning of March until autumn, and the life cycle takes about 55 days (Bambara and Casey, 2003).

Notes on Natural Enemies

Top of page The immature stages 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 that 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. Schedl (1962) records a species of the curculionid genus Scolytoproctus (Scolytoproctus schaumi) which acts as a nest parasite of X. crassiusculus in the Congo. The female Scolytoproctus forces its way into the beetle gallery, and lays its eggs near the gallery entrance. It is unclear, however, whether the ambrosia beetle is killed by the invader, and whether the ambrosia beetle brood continues to develop normally. Most mortality is probably during the dispersal of the adults, and during gallery establishment. The adults of ambrosia beetles are predated by lizards, clerid beetles and ants 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.

Means of Movement and Dispersal

Top of page Natural Dispersal

Adult females fly readily, and flight is one of the main means of movement and dispersal to previously uninfected areas. Of more importance for long distance movement, however, is the transport of infested seedlings, saplings or cut branches. X. crassiusculus usually attacks stems of small diameter (not more than 5 cm diameter), but is sometimes found in larger timber, especially if fresh. Hence it may also be transported in crates or other packing material.

Vector Transmission

The female has a mycangium, a pouch used to carry spores of the ambrosia fungus on which both adult and larvae feed, opening between the pronotum and mesonotum, and extending below the pronotum (Beaver, 1989). The ambrosia fungus of X. crassiusculus is a species of Ambrosiella (Kinuura, 1995; Dute et al., 2002). Ambrosiella spp. are not pathogenic, although they do cause staining of the wood around the gallery systems. 'Contamination ' of the mycangia by the spores of pathogenic fungi is possible. Spores of pathogenic fungi can also be transported on the cuticle of the beetle, although their chance of survival there is much less than in the mycangial pouch. There is some evidence for the transmission of wilt fungi by X. crassiusculus (Davis and Dute, 1997). The species has been reported to vector the sap-stain fungus, Botryodiplodia theobromae, into shade trees (Grevillea robusta) in coffee plantations in India (Sreedharan et al., 1991).

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark adults Yes Pest or symptoms usually visible to the naked eye
Seedlings/Micropropagated plants adults; eggs; larvae; pupae Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
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
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Leaves
Roots
True seeds (inc. grain)

Wood Packaging

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Wood Packaging liable to carry the pest in trade/transportTimber typeUsed as packing
Loose wood packing material No
Solid wood packing material with bark Fresh sapwood Yes
Solid wood packing material without bark Fresh sapwood Yes
Wood Packaging not known to carry the pest in trade/transport
Non-wood
Processed or treated wood

Impact Summary

Top of page
CategoryImpact
Animal/plant collections Negative
Animal/plant products None
Biodiversity (generally) None
Crop production Negative
Environment (generally) None
Fisheries / aquaculture None
Forestry production Negative
Human health None
Livestock production None
Native fauna None
Native flora Negative
Rare/protected species Negative
Tourism None
Trade/international relations None
Transport/travel None

Impact

Top of page Xylosandrus species are known pests of various forest and agricultural plants, and have the potential to transmit pathogenic fungi to their host plants. X. crassiusculus has been recorded killing saplings of forest trees shortly after transplanting. Browne (1968) notes 'devastating' attacks on newly formed plantations of Aucoumea klaineana and Khaya ivoriensis in Ghana. It has also been found in apparently healthy Cinchona trees in Java, Indonesia (Kalshoven, 1959). No known stress factors could be associated with primary attacks on peach orchards in South Carolina, USA (Kovach and Gorsuch, 1985). Atkinson et al. (2000) note large numbers of attacks in Florida, USA on Shumard oak saplings which showed no other symptoms of stress, disease or attack by other insects, and consider that the beetles caused the death of the trees. Atkinson et al. (2000) also noted isolated attacks on large Drake elm saplings. The attacks did not kill the tree directly, but large cankers developed at the site of the attacks, and these sometimes resulted in the death of the trees by girdling. The species can breed successfully in newly sawn timber (Browne, 1961).

Impact: Biodiversity

Top of page Samuelson (1981) notes that in Hawaii, X. crassiusculus has spread into native forest environments, where its hosts include the important endemic trees, Acacia koa and Metrosideros collina. Maeto et al. (1999) noted a large influx of the species from oil palm plantations, where it breeds in fallen palm leaf stalks, into lowland rain forest in Peninsular Malaysia.

Detection and Inspection

Top of page Some success in the detection of the beetle has been obtained by using traps baited with ethanol placed in and around port facilities where infested material may be stored, and around nurseries with plants susceptible to attack. A simple type of trap is described by Bambara et al. (2002). 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. In X. crassiusculus, the frass is pushed out in the form of a compact cylinder, which may reach a length of 3 to 4 cm before it breaks off, and forms a useful recognition character for the presence of attacks.

Prevention and Control

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When Xylosandrus species are detected in plant material, it is necessary to immediately destroy all of the infested material. When they are detected in traps, plant material in the vicinity of the trap should be inspected, with special attention directed towards imported woody products such as crating, dunnage and lumber milling scraps. If an active infestation is detected, chemical control using insecticides is not generally effective since the adult beetles bore deep into the host material. The following insecticides were found to be effective against a species of Euwallacea, destructive to tea: fenvalerate, deltamethrin, quinalphos and cypermethrin (Muraleedharan, 1995); these insecticides may also be effective against other ambrosia beetles. Bambara and Casey (2003) suggest the use of permethrin, but multiple treatments may be required during a season. They suggest the use of some attacked trees as trap trees, which need to be removed and burned before the life cycle of the beetle (about 55 days in North Carolina, USA) is completed. The concealed habitats in which these species feed and reproduce, the difficulties and high costs of insecticide application, and environmental concerns, all limit the effectiveness of chemical control. The use of radiation to kill, sterilize or inhibit the emergence of beetles in cut timber (Yoshida et al., 1975), is unlikely to be practical.

References

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Links to Websites

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GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gatewayhttps://doi.org/10.5061/dryad.m93f6Data source for updated system data added to species habitat list.

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