Xylosandrus mutilatus

 
IDENTITY
Name:   Xylosandrus mutilatus
Pest Authorities:  (Blandford)
Taxonomic Position:  Insecta: Coleoptera: Scolytidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
Synonym(s):
   Xyleborus banjoewangi Schedl
   Xyleborus sampsoni Eggers
   Xyleborus taitinus Eggers
 
RISK RATING SUMMARY
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Uncertain
Uncertainty in this assessment results from: Although this insect is established in at least two southeastern states in the U.S., its ability to adapt to new hosts, compete with indigenous ambrosia beetles or cause significant damage is not known.

RISK RATING DETAILS
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: Xylosandrus mutilatus is established in two states in the southeastern U.S. Several adults were collected in traps near Starkville, Mississippi in 1999. By 2002, thousands of specimens were collected in traps in 10 counties in Mississippi: Attala, Clay, Choctaw, Leake, Lowndes, Madison, Noxubee, Oktibbeha, Webster and Winston. In 2002, specimens were also collected in a trap in Highlands County, Florida. Based on this information, this species appears to be well established in Mississippi and possibly Florida. Several other species of Xylosandrus are already established in the United States, as well as many other sub-tropical and temperate countries (Wood and Bright 1992). 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 and have a high probability of reproducing after introduction.

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. Three species of Xylosandrus have been introduced and established in the U.S., probably as a result of transport of infested wood products in international trade. For example, Xylosandrus crassiusculus was first detected in South Carolina in 1974 (Anderson, 1974) and by the mid-1990's spread throughout most states from Maryland to Texas (Ree and Hunter 1995). X. multilatus has a high reproductive potential, a broad host range and 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: Xylosandrus mutilatus and other ambrosia beetles construct galleries in the xylem of host trees. These galleries, and the staining caused by their associated fungi, degrade wood products. 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. It is also a potential vector of pathogenic fungi. Moreover, plant quarantine measures designed to slow its rate of spread could have an adverse effect on transport of hardwood logs and lumber from infested to uninfested areas.

Since this insect appears to have a preference for small diameter material, it could become a pest of urban trees, especially those stressed by recent planting. Both Xylosandrus germanus and X. crassiusculus have been seen attacking healthy to slightly stressed nursery and landscape trees (Rabaglia, personal observation). Many of these trees most likely would have survived if they weren’t mass attacked.

Environmental Potential Is Low Risk
The relevant criteria chosen for this organism are:  
Justification: Xylosandrus mutilatus is not expected to have a significant adverse environmental impact, provided that it confines its attacks to weakened and dying trees. It is unknown, however, how this species will behave in a new environment, if it will attack young trees (it seems to prefer trees <5 cm DBH in Japan), or if it will become a vector of pathogenic fungi.

 
HOSTS
Xylosandrus mutilatus has a wide host range. Reported hosts in its natural range include: Acer spp., Albizzia spp., Benzoin spp., Camellia spp., Carpinus laxiflora, Castanea spp., Cinnamomum camphora, Cornus spp., Cryptomeria japonica, Fagus crenata, Lindera erythrocarpa, Machilus thurnbergii, Ormosia hosiei, Osmanthus fragrans, Parabezion praecox, Platycarpa spp., and Sweitenia macrophylla (Texas A&M University 2003).

Hosts in the southeastern U.S., where this insect has become established, are presently unknown.

 
GEOGRAPHICAL DISTRIBUTION
Asia:
      This insect is indigenous to Asia and is reported from China (Anhui, Sichuan, Yunnan and Zhejiang Provinces), India (Adaman Islands, Assam), Indonesia (Batoe, Borneo, Java, Sumatra), Japan, Korea, Malaya, Myanmar, Papua New Guinea, Sri Lanka, Taiwan and Thailand (Texas A&M University 2003).
North America:
     Xylosandrus mutilatus is established in Florida and Mississippi, USA.
 
BIOLOGY
The genus Xylosandrus contains 52 species, most of which are native to Southeast Asia. Five species are presently known from the U.S., four of which have been introduced from Asia (X. compactus, X. crassiusculus, X. germanus and X. mutilatus) (Wood and Bright 1992). The genus Xylosandrus is morphologically and biologically closely related to Xyleborus, and many species were originally described as Xyleborus. All are ambrosia beetles (Texas A&M University 2003).

Most of the literature on Xylosandrus mutilatus discusses its taxonomic status and distribution. Little information is available on its biology and ecology. Kajimura and Hijii (1992 and 1994) detail its life history and fungal associates in Japan. In the Aichi Prefecture in central Japan at 980 m above sea level, X. mutilatus has one generation a year. Adult flight occurs from June through August. Female adults bore a horizontal tunnel into the wood to construct a gallery, which extends vertically for 1-4 cm, and larval cradles. The female then innoculates the gallery walls with its associated ambrosia fungus. Each female lays between 1-38 eggs (average of 10) in the gallery system, depending on the length of the gallery. After oviposition, the females maintain the gallery and protect its entrance.

Egg hatching begins about one week after oviposition and the larvae feed on the white colored mycelium of the ambrosia fungus. Pupation occurs within 2-3 weeks in the black-stained larval cradles and pupation lasts about 7 days. As is typical of xyleborine ambrosia beetles, X. mutilatus has extremely inbred polygamy. Immediately after emergence, adult males mate with several of their later-emerging female siblings. Adult males soon die in or near their galleries, while the females either remain in the galleries or emerge in search of new hosts.

 
PEST SIGNIFICANCE
Economic Impact:    Xylosandrus mutilatus constructs galleries in the xylem and associated ambrosia fungi stain the wood. This can cause significant loss of grade and value of wood products.

The fungal associates of X. mutilatus do not appear to be pathogenic. Kajimura and Hijii (1992) found a species of Ambrosiella species (the main larval food source), as well as a Candida species (a yeast) and a Paecilomyces species in the galleries of X. mutilatus. Other species of Xylosandrus have been found to carry and innoculate their host trees with pathogenic fungi. For example, Fusarium solani was found associated with Xylosandrus germanus on tulip poplar, Liriodendron tulipifera, (Anderson and Hoffard 1978), and black walnut, Juglans nigra (Kessler 1994). Xylosandrus crassiusculus has been associated with a sap stain fungus, Bothryodiplodia, in coffee (Sreedharan et al. 1991) and an unidentified species of Fusarium (Davis and Dute 1997).

Environmental Impact:   It is not likely that this species has widespread adverse environmental impacts in its natural range because it attacks weakened trees and is part of a complex of insects involved in the decomposition of dead trees.

Control:    Control of ambrosia beetles is often difficult and impractical. Some insecticides may be effective as preventative treatments or on infested material. Heat, water and fumigants are also used on wood products infested by ambrosia beetles. Checkered beetles (Coleoptera: Cleridae) are common predators of bark and ambrosia beetles, but there are no records of species associated with Xylosandrus sp.

 
DETECTION AND IDENTIFICATION
Symptoms:    Symptoms of attack by xyleborine ambrosia beetles include pin-hole-sized holes in the bark that are either bleeding or have a light colored boring dust. At least two other species of Xylosandrus have characteristic, toothpick-like, curling frass at the entrance holes. The galleries in the xylem consist of a short horizontal entrance and a 1-4 cm long central, vertical gallery with short brood chambers. Attacked trees may have wilting foliage or twig dieback.

Morphology:    Like other species of the tribe Xyleborini, the head of species of Xylosandrus is completely hidden by the pronotum in dorsal view, the antennal club appears obliquely cut, and the body is generally smooth and shining. Xylosandrus spp. are distinguished from related genera (Xyleborus, Xyleborinus, Ambrosiodmus) by the stout body, truncate elytral declivity, and non-contiguous procoxae.

Xylosandrus mutilatus is larger (>3 mm) than any other species of Xylosandrus present in the U.S., but is most easily recognized by the elytra, which are shorter than the pronotum. Like X. crassiusculus, its declivity is without punctures, dull and granulate, but it can be separated from X. crassiusculus by the very steep declivity, the short elytra and the more uniformly dark brown to black color.

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.

 
MEANS OF MOVEMENT AND DISPERSAL
Female adults are capable of flight and are also subject to dispersal by air currents. Both factors are means of local spread. International transport of wood products containing adults or immature stages of Xylosandrus has been responsible for the introduction and establishment of three other species into the U.S. of Xyleborus. Infested fuel wood is a potential source of long distance spread after this insect becomes established. Since this species may attack small trees, it may also be transported in nursery stock.

 
BIBLIOGRAPHY
Anderson, D.M. 1974. First record of Xyleborus semiopacus in the continental United States. (Coleoptera: Scolytidae). United States Department of Agriculture, Cooperative Economic Insect Report 24(45-48): 863-864.
Anderson, R.L.; Hoffard, W.H. 1978. Fusarium canker-ambrosia beetle complex on tulip poplar in Ohio. Plant Disease Reporter 62(8): 751.
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.
Davis, M.A.; Dute, R. 1997. Fungal associates of the Asian ambrosia beetle, Xylosandrus crassiusculus. Proceeding of the Southern Nursery Association Research Conference Annual Report 42: 106-112.
Kajimura, H. . Dr. H. Kajimura, Forest Protection Laboratory, School of Agriculture, Nagoya University, Chikusa, Nagoya, Japan. Personal communication, 26 August 2002.
Kajimura, H.; Hijii, N. 1992. Dynamics if the fungal symbionts in the gallery system and the mycangia of the ambrosia beetle, Xylosandrus mutilatus (Blandford) (Coleoptera: Scolytidae) in relation to its life history. Ecological Research 7: 107-117.
Kajimura, H; Hijii, N. 1994. Reproduction and resource utilization of the ambrosia beetle, Xylosandrus mutilatus, in field and experimental populations. Entomologia Experimentalis et Applicata 71: 121-132.
Kessler, K.J. 1974. An apparent symbiosis between Fusarium fungi and ambrosia beetles causes canker on black walnut stems. Plant Disease Reporter 58(11):1044-1047.
Ree, B ; Hunter, L. 1995. Reported distribution of the Asian ambrosia beetle, Xylosandrus crassiusculus (Motschulsky) in the eastern United States and associated host plants. Proceedings of the Southern Nursery Association Research Conference Annual Report 40:187-190.
Sreedharan, K., Balakrishan, M.M., Stephen, S.D.; Krishnamoorthy, B. 1991. A note on the association of wood boring beetles and a fungus with the death of silver oak trees on coffee plantations. Journal of Coffee Research 21: 145-148.
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.
 
AUTHOR(s)
Name(s):
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:        05/09/03

    
Selected images from Forestry Images (www.forestryimages.org)
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1460068

Adult(s)
Photo by Michael C. Thomas,
Florida Department of Agriculture and Consumer Services


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1460067

Adult(s)
Photo by Michael C. Thomas,
Florida Department of Agriculture and Consumer Services