Xyleborus pfeilii (Ratzeburg)

California Pest Rating for
Xyleborus pfeilii (Ratzeburg)
Coleoptera: Curculionidae: Scolytinae
Pest Rating: A



Initiating Event:

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

History & Status:

Background:  Xyleborus pfeilii is a moderate-sized ambrosia beetle.  Females are 3-3.6 mm in length; males are smaller, but rare (Vandenberg et al., 2010).  Reported host trees include alder, beech, elm, maple, oak, pawpaw (Asimina triloba), poplar, and some conifers (Vandenberg et al., 2010; Wood & Bright, 1992).  A broad range of hosts is characteristic of ambrosia beetles, in contrast to more “typical” phloeophagous (phloem-feeding) scolytines.  As in other ambrosia beetles, the larvae feed on fungus in galleries excavated by adult beetles.  Females mate with males prior to dispersing (Kirkendall & Faccoli, 2010).  Little information is available on the biology of this species, but there is nothing in the literature suggesting that it has a significant economic or environmental impact, even though it is widespread in Europe, where it was apparently introduced almost 200 years ago (Kirkendall & Faccoli, 2010).

Worldwide Distribution:  Xyleborus pfeilii has a wide distribution, and is reported from Africa, Asia, Europe, North America, and New Zealand (Wood & Bright, 1992).  Historically, this species was considered to be native to Europe, Asia, and northern Africa.  Recent work suggests that it is native to Asia but was introduced to Europe at an early date (before 1837) (Kirkendall & Faccoli, 2010).  The species has also been introduced to Canada and the United States, where it is now known to occur in Georgia, Maryland, New Jersey, and Oregon (Humble, 2001; Mudge et al., 2001; Vandenberg et al., 2000)).

Official Control:  Xyleborus pfeilii is apparently not under official control by any government.

California Distribution:  Although Xyleborus pfeilii was trapped multiple times in California, there is no information available to suggest that it is still present in the state.

California Interceptions:  Xyleborus pfeilii has been trapped in Sacramento in 2005 (PDR # 1294653) and Placer County in 2003 (1368629 and 1368628).

The risk Xyleborus pfeilii would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Xyleborus pfeilii occurs in areas with temperate and Mediterranean climates (Kirkendall & Faccoli, 2010). The beetle is probably capable of becoming established in much of California.  This species has been reported to feed on many tree genera; members of these genera are distributed across California.  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: The reported hosts of Xyleborus pfeilii include multiple genera of broadleaf as well as coniferous trees. A broad host range is typical of ambrosia beetles.  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: There is evidence suggesting that ambrosia beetles that have brother-sister mating, which is the case with pfeilii, have an enhanced ability to disperse and colonize new areas. A single female can found a new population, and she does not have to be fertilized.  She can produce sons from unfertilized eggs and mate with them.  Movement of infested firewood would achieve rapid, long-distance dispersal.  In addition, X. pfeilii flies (specimens have been caught with funnel traps) (Humble, 2001; Mudge et al., 2001).  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: Xyleborus pfeilii does not appear to have any recognized economic impact, even though it was introduced to much of Europe and has been present there for almost 200 years.  There is some doubt that economically-important trees in California would be significantly impacted, considering that most such trees are probably members of genera well-represented in Europe, and this beetle is apparently not a significant pest there.  There is the chance that it could vector a plant-pathogenic fungus to economically-important trees.  Therefore, it receives a Low (1) in this category.

Economic Impact:  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: 1

– 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: Xyleborus pfeilii is not known to have had an environmental impact in Europe. There is a chance, however, that this species could have a different impact in the environment of California, where there are tree species not found in Europe.  Ambrosia beetles are less constrained in their host plant choices, and this makes it more difficult to predict what trees might be attacked in a new environment.  Therefore, it receives a High (3) in this category.

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

Environmental Impact: A, B

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: 3

– 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 Xyleborus pfeilii: High (13)

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: Although there are a few trapping records of this beetle from more than ten years ago, there is no further evidence of its occurrence 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:

The final score is the consequences of introduction score minus the post entry distribution and survey information score: High (13)


There is uncertainty regarding two components of this pest rating proposal.  First, there is uncertainty regarding the possible presence of this species in the state.  This beetle was trapped multiple times in two counties.  There do not appear to have been any collections of this species in California since the last of these trappings in 2005, and it is presumed that it is not established in the state.  Second, there is uncertainty regarding the possible impact of this species in California.  Lack of impact in Europe does not mean this species could not have economic and/or environmental impacts in California.  Part of this uncertainty is the possibility of X. pfeilii interacting with plant-pathogenic fungal species that are already present in California.

Conclusion and Rating Justification:

There is no evidence that Xyleborus pfeilii causes economic or environmental damage anywhere it is known to have been introduced.  This includes the large area it has invaded in Europe over the past two centuries.  However, it seems that a cautious approach is best with possible forest pests.  The behavior of this beetle may be very different in the environments of California.  At least one introduced species in the genus Xyleborus, X. glabratus, has become a serious pest species in the southeastern United States; it is having a significant impact on the environment and it threatens the avocado industry (Hughes et al., 2016).  The fungus symbiosis in this genus raises special concerns; X. pfeilii could bring with it new (to California) pathogenic fungi, or it could interact in a new way with fungi already here.  For these reasons, an “A” rating is justified.


Kirkendall, L.R. & Faccoli, M.  2010.  Bark beetles and pinhole borers (Curculionidae, Scolytinae, Platypodinae) alien to Europe.  Zoo Keys.  56: 227-251.

Hughes, M.A., Smith, J.A., & Coyle, D.R.  2016.  Biology, ecology, and management of laurel wilt and the redbay ambrosia beetle.  Southern Regional Extension Forestry Forest Health.  November 2016: 1-6.

Humble, L.M.  2001.  Invasive bark and wood-boring beetles in British Columbia, Canada.  Pages 69-77 in R.I. Alfaro, K.R. Day, S.M. Salom, K.S.S Nair, H.F. Evans, A.M. Liebhold, F. Lieutier, M. Wagner, K. Futai, & K. Suzuki, editors. Protection of World Forests: Advances in Research, Proceedings: XXI IUFRO World Congress. August 7-12, 2001, Kuala Lumpur, Malaysia. IUFRO Secretariat, Vienna, IUFRO World Series Vol. 11. 253 p.

Mercado, J.E. 2010. Bark beetle genera of the United States. Colorado State University, USDA-APHIS-PPQ Center for Plant Health Science and Technology, and USDA-FS Rocky Mountain Research Station. http://idtools.org/id/wbb/bbgus

Mudge, A.D., LaBonte, J.R., Johnson, K.J.R., & LaGasa, E.H.  2001.  Exotic woodboring Coleoptera (Micromalthidae, Scolytidae) and Hymenoptera (Xiphyriidae) new to Oregon and Washington.  103(4): 1011-1019.

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(1): 62-68.

Vega, F.E. & Hofstetter, R.W.  2014.  Bark beetles: Biology and ecology of native and invasive species.  Academic Press.  640 pp.


Kyle Beucke, 1220 N Street, Room 221, Sacramento, CA, 95814, 916-403-6741, plant.health[@]cdfa.ca.gov

Responsible Party:

Jason Leathers, 2800 Gateway Oaks, Sacramento CA 95833, (916) 654-1211, plant.health[@]cdfa.ca.gov

Comment Period:* CLOSED

4/24/18 – 6/8/18


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Pest Rating: A


Posted by ls