Xyleborus glabratus

Name:   Xyleborus glabratus
Pest Authorities:  Eichhoff
Taxonomic Position:  Insecta: Coleoptera: Scolytidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
   Ambrosiakäfer (German)
   Holzborher (German)
   Redbay ambrosia beetle (English)
   Xylébore (French)
   Xyleboro (Italian and Portuguese)
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Certain
Uncertainty in this assessment results from: This species is currently causing mortality of redbay and related species in the southeastern US

Establishment Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism has successfully established in location(s) outside its native distribution
  • Suitable climatic conditions and suitable host material coincide with ports of entry or major destinations.
  • Organism has demonstrated ability to utilize new hosts
  • Organism has active, directed host searching capability or is vectored by an organism with directed, host searching capability.
  • Organism has high inoculum potential or high likelihood of reproducing after entry.
Justification: The first Xyleborus glabratus adults in North America were collected in traps in Port Wentworth, Georgia in 2002. Since then the beetle has been found in more than 30 counties in Georgia, South Carolina and Florida. (See http://www.fs.fed.us/r8/foresthealth/laurelwilt/index.shtml for the most current distribution.)

Spread Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is capable of dispersing more than several km per year through its own movement or by abiotic factors (such as wind, water or vectors).
  • Organism has demonstrated the ability for redistribution through human-assisted transport.
  • Organism has a high reproductive potential
  • Potential hosts have contiguous distribution.
  • Newly established populations may go undetected for many years due to cryptic nature, concealed activity, slow development of damage symptoms, or misdiagnosis.
  • Eradication techniques are unknown, infeasible, or expected to be ineffective.
Justification: Female adults are believed capable of flight and could travel 2-3 km in search of suitable hosts. Moreover they are subject to dispersal by air currents. Koch and Smith (2008) estimate spread rates and predicte this species may spread throughout the range of redbay in < 40 years. Other species of Xyleborus have been introduced and established in new locations due to transport of infested wood products. This insect has cryptic habits, which would make it difficult to detect and eradicate.

Economic Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism attacks hosts or products with significant commercial value (such as for timber, pulp, or wood products.
  • Organism directly causes tree mortality or predisposes host to mortality by other organisms.
  • Damage by organism causes a decrease in value of the host affected, for instance, by lowering its market price, increasing cost of production, maintenance, or mitigation, or reducing value of property where it is located.
  • Organism may cause loss of markets (domestic or foreign) due to presence and quarantine significant status.
  • No effective control measure exists.
  • Organism has potential to be a more efficient vector of a native or introduced pest.
Justification: This species vectors a pathogenic fungus which causes mortlaity of redbay and related species. Economic impacts may be significant in the loss of landscape redbay. Most important may be the economic impacts in avocado.

Environmental Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is expected to cause significant direct environmental effects, such as extensive ecological disruption or large scale reduction of biodiversity.
  • Organism is expected to have direct impacts on species listed by Federal, Provincial, or State agencies as endangered, threatened, or candidate. An example would be insuring a listed plant species.
  • Organism is expected to have indirect impacts on species listed by Federal, Provincial, or State agencies as endangered, threatened, or candidate. This may include disruption of sensitive or critical habitat.
  • Organism may attack host with small native range.
Justification: the extensive mortality of redbay that this species and its fungal assocate cause may have significant environmental impacts. Loss of redbay, a mid-story component of coastal plain forests, could effect birds and other wildlife. Redbay is also a larval host of the palmedes swallowtail butterfly.

Known host trees in this insect’s natural range include an Asian spicebush, Lindera latifolia; yellow litsea, Litsea elongata and sal, Shorea robusta, (Wood and Bright 1992). Maiti and Saha (2204) reference Phoebe lanceolata as a host in India and in japan Murayama (1936) lists Lithocarpus edulis as a host.

In the US, this beetle has been found infesting: redbay (Persia borbonia L. Spreng., sassafras ( Sassafras albidum , and avocado ( Persia americanum ).

     Xyleborus glabratus is indigenous to India (Assam, Bengal), Japan (and the Bonin Islands), Myanmar and Taiwan (Wood and Bright 1992).
North America:
      This beetle was first collected in North America in Port Wentowrth, Georgia, U.S., it has since been found in more than 30 counties in Georgia, South Carolina and Florida.
The genus Xyleborus is a large and diverse genus of ambrosia beetles. As it is currently recognized, there are more than 500 species in the genus, which are found in all continents except Antarctica. The greatest species diversity occurs in the tropics (Wood and Bright 1992). In general, species of Xyleborus have a wide host range. Seventeen species of Xyleborus are known from North America. All are of minor economic importance (Furniss and Carolin 1977).

Most species of Xyleborus attack weakened or recently cut woody plants, and representatives of the genus can be found attacking virtually all parts of a host plant. These ambrosia beetles culture a fungus on the walls of their galleries, and larvae feed on the fungus within the parental galleries. Males are dwarfed, haploid and flightless. Only the females seek a new host and establish galleries. The ratio of females to males is often 15:1 or greater.

When first found in North America there was little information available on the life history and habits of Xyleborus glabratus. In 2004, Xyleborus glabratus were found in dying redbay trees on Hilton Head Island, South Carolina (Rabaglia et al 2006). The beetle was later found infesting redbay trees along the coast of South Carolina, Georgia and Florida (Fraedrich et al 2007). It has since been shown that the beetle's fungal symbiont ( Raffaelea sp.) is causing a wilt disease (laurel wilt) that has killed redbay and several other Lauraceae (Fraedrich et al 2007).

Economic Impact:    This species is vectoring a pathogenic fungus that is causing a wilt disease in redbay and several other related hosts (Fraedrcih et al, 2007). The economic impacts of this deases can be significant. More than 90% mortality of redbay has been documented in several locations. Redbay is often an ornamental tree in parts of the southeastern coast. The most significant impact my be on avocado. The beetle and fungus were recently found in an ornamental avocado near Jacksonville, Florida.

Environmental Impact:   This species is vectoring a very pathogenic fungus that causes mortality in redbay and related speces. Redbay is a mid-story tree along the coastal plain from North Carolina to Texas. In some locations redbay mortality exceeded 90%. The palmedes swallowtail butterfly is dependant upon redbay as a larval host.

Control:    Little information is available on the control of xyleborine ambrosia beetles. In general, checkered beetles (Coleoptera: Cleridae) beetles are predators of bark and ambrosia beetles, but there are no records of specific associated predators or parasitoids. Chemical insecticide treatments may be effective as a preventative, or in the treatment of infested material. Heat and water treatments are also used to control ambrosia beetles.

Symptoms:    Symptoms of attack by xyleborine ambrosia beetles, including Xyleborus glabratus, are pinhole-sized holes in the bark that are either bleeding or have light-colored boring dust and characteristic galleries in the wood of infested trees. Similar to Xylosandrus species, Xyleborus glabratus makes frass tubes that appear as tooth picks that extend out from the bark.

Morphology:    Xyleborus adults are small, 2.0-3.0 mm long, and oblong. When viewed from above, the prothorax conceals the head. Like Ips spp., some Xyleborus have irregular teeth or spines on the posterior of the elytra. These insects, however, have a more shallow declivity thanIps and no shelf at the base of the elytra. Xyleborus sp. have a bell shaped pronotum that is wider than the anterior portion of the elytra.

Xyleborus glabratus adults are small beetles, 2.0 mm long, slender, and brown-black in color. They can be distinguished from other species of Xyleborus found in North America by the following characters found on the declivity: The declivity is steep and convex, especially on the posterior portion; the punctures are relatively large (larger and deeper than on the elytral disc), and the surface is shinny. The posterio-lateral portion of the declivity has a distinct raised, almost carinate margin. The first interstriae have a distinct tubercle at the middle of the declivity, and interstria 3 has a much smaller tubercle at about the same position.

Larvae are typical Scolytidae, white colored c-shaped, legless grubs with an amber colored head capsule.

Testing Methods for Identification:    Examination of adults by a taxonomist with expertise in the family Scolytidae is required for positive identification to species. The adults and larval galleries have sufficient characteristics to permit entomologists to make field identifications at least to genus.

Female adults are capable of flight and are also subject to dispersal by air currents. Both factors are means of local spread. Another potential means of local spread is transport of fuelwood, tree trimmings and other infested wood products. International transport of wood products containing adults or immature stages of Xyleborus has been responsible for the introduction and establishment of other species of Xyleborus. This is undoubtedly the means by which X. glabratus was introduced into Georgia.

Atkinson, T.H.; Rabaglia, R.J.; Bright, D.E. 1990. Newly detected exotic species of Xyleborus (Coleoptera) with a revised key to species in eastern North America. Canadian Entomologist 122: 93-104.
Fraedrich, S.W., T.C. Harrington, R.J. Rabaglia, M.D. Ulyshen, A. E. Mayfield III, J.L. Hanula, J.M. Eickwort and D. R. Miller. 2008. A fungal symbiont of the redbay ambrosia beetle causes a lethal wilt in redbay and other Lauraceae in the southeastern USA Plant Disease 92:215-224.
Rabaglia, R.J., S.A. Dole and A.I. Cognato 2006. Review of the American Xyleborina occurring north of Mexico, with an illustrated key. Annals of the Entomological Society of America 99(6):1034-1056.
Vandenberg, N.J.; Rabaglia, R.J.; Bright, D.E. 2000. New records of two Xyleborus (Coleoptera: Scolytidae) in North America. Proceedings of the Entomological Society of Washington 102: 62-68.
Wood, S.L.; Bright, D.E. 1992. A catalog of Scolytidae and Platypodidae (Coleoptera), Part 2: Taxonomic index. Great Basin Naturalist Memoirs 13, 1553 pp.
Robert Rabaglia
Name and Address of the First Author:
Robert Rabaglia
Forest Health Protection
United States Department of Agriculture Forest Service
1601 North kent Street
RPC, 7th Floor (FHP)
Arlington, VA
USA 22209
CREATION DATE:        05/09/03
MODIFICATION DATE:        06/18/08