Xyleborus similis

Name:   Xyleborus similis
Pest Authorities:  Ferrari
Taxonomic Position:  Insecta: Coleoptera: Scolytidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
   Xyleborus bucco Schaufuss
   Xyleborus capito Schaufuss
   Xyleborus dilatatulus Schedl
   Xyleborus dilatus Eichhoff
   Xyleborus ferrugineus Boheman
   Xyleborus novaguineanus Schedl
   Xyleborus parvulus Eichhoff
   Xyleborus submarginatus Blandford
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Uncertain
Uncertainty in this assessment results from: The North American hosts of this insect are not known, nor is its ability to successfully compete with and/ or displace indigenous ambrosia beetles. Moreover, while this insect has been collected in traps in Houston, TX, U.S., there are no indications that it is causing tree damage.

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: Xyleborus similis has become successfully established in several African countries and on a number of Pacific Islands, where it has adapted to many new host plants. This insect is believed established in Houston, Texas. Specimens were collected in traps at Memorial Park in Houston in 2002. Based on the timing and location of these collections, this species is most likely established in the area. Five adults were collected in April and May 2002 and one adult was collected in October 2002. The location of these collections, away from the port and in an urban park, indicates that these are not interceptions. Sixteen additional species of the tribe Xyleborini have become established in North America (Atkinson et al. 1990, Vandenberg et al. 2000). Other North American ports of entry, especially those located in warm climates, would be expected to have suitable climatic conditions and host material for this insect’s establishment. Ambrosia beetles have an active, directed searching capability that allows them to find suitable hosts. X. similis has a demonstrated ability to reproduce after being introduced into new locations.

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.
  • Organism has broad host range.
Justification: Female adults are capable of flight and could travel 2-3 km in search of suitable hosts. Moreover they are subject to dispersal by air currents. This insect has been introduced into a number of African and Pacific Island countries via transport of infested wood products in international trade. More local human assisted transport could occur via movement of infested fuelwood and/or tree trimmings. Xyleborus similis has a broad host range and cryptic habits, which would make it difficult to detect and eradicate. It also has the potential to be a vector of pathogenic fungi.

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: Like most ambrosia beetles, Xyleborus similis constructs galleries in the xylem of its host trees. These galleries and the staining caused by their associated fungi degrade wood products. X. similis has also been implicated as a vector of pathogenic fungi in rubber trees in Malaysia (Browne 1961) and of Fusarium solani on teak in India (Balasundaran and Sankaran 1991). If this insect should attack valuable broadleaf species such as oaks, ash, walnut etc, this insect could have a significant effect on the hardwood lumber industry. Moreover, plant quarantine measures designed to slow the rate of spread could have an adverse effect on transport of broadleaf logs and lumber from infested to uninfested areas.

Environmental Potential Is Low Risk
The relevant criteria chosen for this organism are:  
Justification: Xyleborus similis is expected to have an insignificant adverse environmental impact because it usually confines its attacks weakened trees.

Xyleborus similis has a wide host range. Recorded hosts include Alphitonia petriei, Elaenocarpus sp., Hevea brasiliensis, Shorea robusta (Wood and Bright 1992). Pinus caribaea hondurensis, established in plantations in Fiji has been reported attacked (Beaver 1989). Browne (1961) listed 19 hosts in 14 families in Malaya (Malaysia) as follows: Annonaceae: unidentified species; Apocynaceae: Alstonia spathulata; Araliaceae: Arthrophyllum diversfolium; Dipterocarpaceae: Diprocarpus baudii, Dryobalanops aromatica, Shorea leprosula; Elaeocarpaceae: Elaeocarpus petiolatus; Euphobiaceae: Hevea brasiliensis; Guttiferae: Calophyllum sp., Garcinia sp.; Lauraceae: unidentified species; Leguminosae: Albizzia falcata, Intsia palembanica; Rhizophoraceae: Bruguiera parviflora, Pellacalyx saccardiana; Sterculiaceae: Sterculia macrophylla; Styracaceae: Styrax benzoin; Urticaceae: Artocarpus schortechinii; Verbenaceae: Vitex pubescens, Sterculia conwentzii, Ficus spp. in plantations in Papua New Guinea (Gray 1974) and Cocos nucifera in Sri Lanka (Mahindapala and Subasinghe 1976). Bright and Skidmore (1997) state that Ohno (1990) lists many hosts and Wood and Bright (1992) state that Schedl (1968) also lists many hosts.

The North American hosts of this insect have not been identified.

     This insect is introduced and established in the Cameroon, Kenya, Madagascar, Mauritania, Mauritius Island, the Seychelles Islands and Tanzania.
     Xyleborus similis is indigenous to China (Guangdong Province), India (Andaman Islands), Japan (Bonin Islands), Jordan, Malaysia (Malaya, Sarawak), Myanmar, Nepal, Pakistan, Sri Lanka, Taiwan, Thailand and Vietnam (Tonkin Island). This insect has also been recently collected in Indonesia (Bali) (Bright and Skidmore 2002).
Australasia & South Pacific:
     Introduced into Australia, Christmas Island, Fiji, Indonesia (Bali, Batoe, Borneo, Celebes, Java, Mentawei, Sumatra), Kiribati Islands, Micronesia (Caroline Islands, Guam, Kusaie, Marshall Islands, Palau Islands, Ponape, Truk), New Caledonia, Papua New Guinea (New Guinea, Bismark Islands, Admiralty Islands), Philippine Islands, Samoan Islands, Solomon Islands, Tahiti Islands Wood and Bright (1992) record Xyleborus similis from Hawaii, but Samuelson (1981) contends that previous accounts from Hawaii were the result of misidentifications and confusions with synonyms.
North America:
     Introduced into the U.S. in Houston, TX and believed established.
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 Xyleborusare 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.

Xyleborus similis has a wide host range and attacks unhealthy trees and cut logs (Browne 1961). Beaver (1989) states that it normally breeds in fallen or very unhealthy trees, but may occasionally attack healthy trees through bark wounds. The gallery system is reported to resemble that of X. affinis Eichhoff and X. perforans Wollaston) (Beaver 1988, Beaver 1989). Wood (1960) and Beaver (1989) report collecting this species at lights, and Gray (1974) collected it during the day on sticky traps. In Tanzania, X. similis flight activity peaks in June, July and August, which coincides with a period of high rainfall.

Economic Impact:    The greatest economic impact of Xyleborus similis is degradation of logs and wood products caused by gallery construction by adults and wood staining by ambrosia fungi.

Perhaps more importantly, X. similis, like many other xyleborines, has been implicated as a vector of pathogenic fungi. While the ambrosia fungus carried by this insect is usually not pathogenic, contaminants may be pathogenic in certain hosts. Xyleborus similis has been suspected of being a vector of a disease of rubber trees in Malaysia (Browne 1961) and of Fusarium solani on teak in India (Balasundaran and Sankaran 1991).

Environmental Impact:   Since Xyleborus similis confines its attacks to weakened trees, it has no adverse environmental impact. It functions as part of a complex of insects that contribute to the decomposition of dead wood.

Control:    Little information is available on the control of xyleborine ambrosia beetles. In general, checkered beetles (Coleoptera: Cleridae) 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 similis, are usually pinhole-sized holes in the bark that are either bleeding or have light-colored boring dust. The gallery system in the xylem consists of branched tunnels, without brood chambers, similar to the galleries of Xyleborus affinis. Attacked trees may also show signs of wilting and twig dieback.

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 than Ips and no shelf at the base of the elytra. Xyleborus has a bell shaped pronotum that is wider than the anterior portion of the elytra.

Adult Xyleborus similis average 2.5 mm in length, and are slender reddish-brown beetles typical of the genus Xyleborus. They are readily distinguished from North American Xyleborus by the 1st (sutural) striae conspicuously diverging from the suture around the second and largest of three tubercles on the declivity.

Larvae are typical Scolytidae. They are white, 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 means of local spread is movement of infested fuelwood, tree trimmings or other infested items. International transport of wood products containing adults or immature stages of Xyleborus similis has been responsible for the introduction of this insect into Africa and a number of Pacific Islands. This is undoubtedly the means by which it was introduced into Texas.

Atkinson, T.H.; Rabaglia, R.J.; Bright, D.E. 1990. Newly detected species of Xyleborus (Coleoptera: Scolytidae) with a revised key to species in eastern North America. Canadian Entomologist 122: 93-104.
Balasundaran, M.; Sankaran, K.V. 1991. Fusarium solani associated with stem cankers and dieback of teak in southern India. Indian Forester 117: 147-149.
Beaver, R.A. 1989. Bark and ambrosia beetles (Coleoptera: Scolytidae) newly recorded from Fiji, and their economic importance. Southern Pacific Journal of Natural Science 9:1-7.
Beaver, R.A. 1988. Biological studies on ambrosia beetles of the Seychelles. Journal of Applied Entomology 105: 62-73.
Bright, D.E.; Skidmore, R.E. 1997. A catalog of Scolytidae and Platypodidae (Coleoptera), Supplement 1 (1990-1994). National Research Council of Canada Press, Ottawa, Canada. 368 pp.
Browne, F.G. 1961. The biology of Malayan Scolytidae and Platypodidae. Malayan Forest Records, Number 22. 255 pp.
Gray, B. 1974. Observations on insect flight in a tropical forest plantation. IV. Flight activity of Scolytidae (Coleoptera). Zeitschrift für Angewandte Entomologie 75(2): 178-186.
Maddoff, S.S.; Bakke, A. 1995. Seasonal fluctuations and diversity of bark and woodboring beetles in lowland forest: implications for management practices. South African Forestry Journal 173: 9-15.
Mahindapala, R.; Subasinghe, S.M.P. 1976. Damage to coconut by Xyleborus similis. FAO Plant Protection Bulletin 24: 45-47.
Ohno, S. 1990.. The Scolytidae and Platypodidae (Coleoptera) from Borneo found in logs at Nagoya Port 1. Research Bulletin of the Plant Protection Service (Japan) 6:83-94.
Samuelson, G.A. 1981.. A synopsis of Hawaiian Xyleborini (Coleoptera: Scolytidae). Pacific Insects 23(1-2):50-92.
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. 1960.. Insects of Micronesia, Coleoptera: Platypodidae and Scolytidae. Bernice P. Bishop Museum, Insects of Micronesia, 18(1):1:73.
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:        05/07/03
MODIFICATION DATE:        05/07/03