Black Timber Bark Beetle | Xylosandrus germanus (Blandford)

California Pest Rating for
Black Timber Bark Beetle | Xylosandrus germanus (Blandford)
Coleoptera: Curculionidae: Scolytinae
Pest Rating: A




Initiating Event:

Xylosandrus germanus is currently Q-rated.  A permanent pest rating proposal is required to support an official pest rating.

History & Status:

Background: Xylosandrus germanus is a moderate-sized (2-2.3 mm in length), dark brown ambrosia beetle (Wood, 1982).  The beetle is reported to feed on over 200 species of broadleaved and coniferous trees, including species in the following genera: Acer, Carya, Cornus, Fagus, Fraxinus, Juglans, Malus, Myrica, Liriodendron, Pinus, Prunus, Pyrus, Quercus, and Ulmus. It feeds on live trees and cut wood (Wood, 1982).  This beetle has been reported to attack a variety of economically-important trees, including chestnut in Tennessee (Oliver and Mannion, 2001), flood-stressed flowering dogwood in Ohio (Ranger et al., 2015), walnut (Katovitch, 2014; Reed et al., 2015), and apple in New York (Agnello et al., 2016).  It has been suggested that this beetle may primarily attack trees that are stressed, even if this stress is not visually apparent (Ranger et al., 2015).  If this is the case, one possible explanation is that healthy trees resist the establishment of ambrosia fungus.  Besides the symbiotic ambrosia fungus, other fungi have been found in the galleries of X. germanus, including Fusarium species, which can be pathogenic (Ranger et al., 2016).  Thus, it is possible that X. germanus is involved with the spread of plant pathogenic fungi.   This beetle has also been reported to damage cut spruce and fir timber in Switzerland (Graf and Manser, 2000).  Adult females X. germanus mate with males before leaving their gallery, and they can also reproduce via arrhenotokous parthenogenesis: an unmated female lays unfertilized eggs that develop into males. The female mates with her male progeny and then deposits fertilized eggs, which develop into females (Wood, 1982).

Worldwide Distribution:  Xylosandrus germanus is native to Asia (Japan, Taiwan, Korea, China, and Vietnam).  It has been introduced to Europe, Canada (British Columbia), and the United States (Oregon, though possibly eradicated in that state, Hawaii, and the eastern United States) (LaBonte et al., 2005).

Official Control: Xylosandrus germanus does not appear to be under official control anywhere.

California Distribution:  Xylosandrus germanus is not known to be present in the state of California (Bright and Stark, 1973; Symbiota Collections of Arthropods Network).

California Interceptions: Xylosandrus germanus has apparently not been intercepted on incoming shipments in California, but was trapped in 2003 in Los Angeles County with a Lindgren funnel (PDR # 1368627).  This is the only available record for California, and the species is presumed to not be present in the state.

The risk Xylosandrus germanus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Xylosandrus germanus has demonstrated an ability to become established over a large area worldwide, and a large portion of California has a climate suitable for the establishment of this species. The list of reported hosts for germanus is extensive (>200 species) and includes genera that are broadly distributed across the state, both as native forest trees as well as ornamental and crop trees.  Therefore, it receives a High (3) in this category.

– Low (1) Not likely to establish in California; or likely to establish in very limited areas.

– Medium (2) may be able to establish in a larger but limited part of California.

– High (3) likely to establish a widespread distribution in California.

2) Known Pest Host Range: Xylosandrus germanus is reported to feed on over 200 species of plants in many genera. Therefore, it receives a High (3) in this category.

– Low (1) has a very limited host range.

– Medium (2) has a moderate host range.

– High (3) has a wide host range.

3) Pest Dispersal Potential: Adult female Xylosandrus germanus Sibling mating and arrhenotokous parthenogenesis mean a single female is capable of founding a population.  Therefore, it receives a High (3) in this category.

– Low (1) does not have high reproductive or dispersal potential.

– Medium (2) has either high reproductive or dispersal potential.

– High (3) has both high reproduction and dispersal potential.

4) Economic Impact: This species has been reported to attack a range of ornamental and fruit (e.g., apple) trees.  Even if attacks do not result in the death of the tree, growth and aesthetics are impacted.  This species causes damage to cut timber as well.  All ambrosia beetles carry fungi; besides the symbiotic fungus, germanus could vector other, potentially pathogenic fungi.  Therefore, it receives a Medium (2) in this category.

Economic Impact:  A, E

A. The pest could lower crop yield.

B. The pest could lower crop value (includes increasing crop production costs).

C. The pest could trigger the loss of markets (includes quarantines).

D. The pest could negatively change normal cultural practices.

E. The pest can vector, or is vectored, by another pestiferous organism.

F. The organism is injurious or poisonous to agriculturally important animals.

G. The organism can interfere with the delivery or supply of water for agricultural uses.

Economic Impact Score: 2

– Low (1) causes 0 or 1 of these impacts.

– Medium (2) causes 2 of these impacts.

– High (3) causes 3 or more of these impacts.

5) Environmental Impact: Although Xylosandrus germanus was introduced to large areas of Europe and the United States and has been present there for decades, environmental impact has been minimal. Therefore, it receives a Low (1) in this category.

Evaluate the environmental impact of the pest on California using the criteria below.

Environmental Impact:

A. The pest could have a significant environmental impact such as lowering biodiversity, disrupting natural communities, or changing ecosystem processes.

B. The pest could directly affect threatened or endangered species.

C. The pest could impact threatened or endangered species by disrupting critical habitats.

D. The pest could trigger additional official or private treatment programs.

E. The pest significantly impacts cultural practices, home/urban gardening or ornamental plantings.

Environmental Impact Score: 1

– Low (1) causes none of the above to occur.

– Medium (2) causes one of the above to occur.

– High (3) causes two or more of the above to occur.

Consequences of Introduction to California for Xylosandrus germanus: Medium (12)

Add up the total score and include it here.

–Low = 5-8 points

–Medium = 9-12 points

–High = 13-15 points

6) Post Entry Distribution and Survey Information: Xylosandrus germanus is not known to be present in the state of California.  It receives a Not established (0) in this category.

–Not established (0) Pest never detected in California, or known only from incursions.

–Low (-1) Pest has a localized distribution in California, or is established in one suitable climate/host area (region).

–Medium (-2) Pest is widespread in California but not fully established in the endangered area, or pest established in two contiguous suitable climate/host areas.

–High (-3) Pest has fully established in the endangered area, or pest is reported in more than two contiguous or non-contiguous suitable climate/host areas.

Final Score:

7) The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (12)


There appears to be a degree of uncertainty regarding the ability of Xylosandrus germanus to attack healthy trees or if only trees that are stressed or compromised are attacked.  If this species only attacks weakened trees, then its potential economic impact may be limited in time and space, although extreme weather associated with climate change could lead to a greater impact.  The lack of evidence of environmental impacts resulting from this species may be an artefact of a lack of study in this area.  Therefore, environmental impact may have been underestimated in this proposal.  The ability of this species (and perhaps ambrosia beetles in general) to carry fungi other than the symbiotic ambrosia fungus means that X. germanus could play a role in the transmission of other tree diseases, perhaps ones that are already present in California.

Conclusion and Rating Justification:

Xylosandrus germanus is an ambrosia beetle that does not appear to be established in California, and it has a demonstrated ability to damage trees.  As already stated, there is uncertainty regarding the ability of X. germanus to attack completely healthy trees.  The author of this proposal is taking a cautious approach.  If significant numbers of trees, whether they be in an ornamental, fruit, or forest setting, are weakened by drought, for instance, and are ultimately killed as a result of ambrosia beetle attack, the economic or environmental impact would be no less important and the ambrosia beetles would have played a critical role in the damage.  For these reasons, an “A” rating is justified.


Agnello, A., Breth, D., Davis, A., and E. Tee.  2016.  Ambrosia beetles (Xylosandrus germanus) infestations and management trials in high-density apple orchards.  Proceedings from the Empire State Producers Expo, Syracuse, N.Y.

Bright Jr., D.E. and R.W. Stark.  1973.  The Bark and Ambrosia Beetles of California.  University of California Press.  169 pp.

Graf, E. and P. Manser.  2000.  Beitrag zum eingeschleppten schwarzen nutzholzborkenkäfer

Xylosandrus germanus. Biologie und schadenpotential an im wald gelagertem rundholz im vergleich zu Xyloterus lineatus und Hylecoetus dermestoides.  Schweizerische Zeitschrift für Forstwesen.  151: 271-281.

Katovich, S.  2014.  Insects attacking black walnut in the Midwestern United States.  pp. 121-126.  In: (C.H. Michler, P.M. Pijut, J.W. Van Sambeek, M.V. Coggeshall, J. Seifert, K. Woeste, R. Overton, F. Ponser Jr., eds.) Black walnut in a new century, proceedings of the 6th Walnut Council research symposium; 2004 July 25-28; Lafayette, IN. Gen. Tech. Rep. NC-243. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Research Station. 188 pp.

LaBonte, J.R., Mudge, A.D., and K.J.R. Johnson.  2005.  Nonindigenous woodboring Coleoptera (Cerambycidae, Curculionidae: Scolytinae) new to Oregon and Washington, 1999-2002: Consequences of the intracontinental movement of raw wood products and solid wood packing materials.  Proceedings of the Entomological Society of Washington.  107(3): 554-564.

Oliver, J.B. and C.M. Mannion.  2001.  Ambrosia beetle (Coleoptera: Scolytidae) species attacking chestnut and captured in ethanol-baited traps in middle Tennessee.  Environmental Entomology.  30(5): 909-918.

Ranger, C.M., Reding, M.E., Schultz, P.B., Oliver, J.B., Frank, S.D., Addesso, K.M., Chong, J.H., Sampson, B., Werle, C., Gill, S., and C. Krause.  2016.  Biology, ecology, and management of nonnative ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) in ornamental plant nurseries.  Journal of Integrated Pest Management.  7(1): 1-23.

Ranger, C.M., Schultz, P.B., Frank, S.D., Chong, J.H., and M.E. Reding.  2015.  Non-native ambrosia beetles as opportunistic exploiters of living but weakened trees.  PLOS One.  1-21.

Reed, S.E., Juzwik, J., English, J.T., and M.D. Ginzel.  2015.  Colonization of artificially stressed black walnut trees by ambrosia beetle, bark beetle, and other weevil species (Coleoptera: Curculionidae) in Indiana and Missouri.  Environmental Entomology.  44(6): 1455-1464.

Symbiota Collections of Arthropods Network.  Accessed February 14, 2018.

Wood, S.L.  1982.  The bark and ambrosia beetles of North and Central America (Coleoptera: Scolytidae), a taxonomic monograph.  Brigham Young University.  1359 pp.


Kyle Beucke, 1220 N Street, Room 221, Sacramento, CA, 95814, 916-403-6741,[@]

Responsible Party:

Jason Leathers, 2800 Gateway Oaks, Sacramento CA 95833, (916) 654-1211,[@]

Comment Period:* CLOSED

4/24/18 – 6/8/18


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Pest Rating: A


Posted by ls