Banded elm bark beetle | Pest Rating Proposals and Final Ratings

California Pest Rating for

Banded Elm Bark Beetle | Scolytus schevyrewi Semenov

Coleoptera

Pest Rating: C

PEST RATING PROFILE

Initiating Event:

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

History & Status:

Background: Scolytus schevyrewi can be recognized by its relatively large size (2.7-4.3 mm in length), the dark band running across the median portions of the elytra, and the position and shape of the abdominal spine. In the United States, this species attacks elms (Ulmus americana, U. pumila, U. thomasii, and U. procera). In its native range, it has been reported feeding on trees in the genera Malus and Prunus. These genera include important fruit trees in California. As of 2005, however, there were no records of this beetle attacking trees other than elms in the United States. The species appears to preferentially attack, or cause greater damage to weakened or stressed trees. Drought stress may be associated with greater damage. Maturation feeding (feeding by adults before mating) occurs on twigs. This beetle is apparently capable of transmitting the Dutch elm disease fungus to otherwise healthy trees, and maturation feeding is one way this could occur.

Worldwide Distribution: Scolytus schevyrewi is native to northern China, Central Asia, and Russia. The beetle was introduced to the United States in 1994 or earlier, as this when the first specimen was collected, but recognition of the species and the fact it was present in the United States took a decade, probably because of the similarity of this species to Scolytus multistriatus. Scolytus schevyrewi is widely distributed in the United States and has been reported from at least 28 states. The species has also been introduced to Canada and Mexico.

Official Control: Scolytus schevyrewi is not known to be under official control anywhere.

California Distribution: Scolytus schevyrewi has been found in at least 13 counties in California, ranging from Lassen County in the north to San Diego County in the south.

California Interceptions: Scolytus schevyrewi has been trapped in 9 counties from 2004-2010 (Kern, Inyo, Lassen, Los Angeles, Mono, Nevada, Sacramento, San Diego, and San Bernardino) (PDR # 5035940, 1355030, 1355032, 1355027, 1355031, 1311668, 1322007, 1322005, 1368633, 1322006).

The risk Scolytus schevyrewi would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Scolytus schevyrewi is already present in at least 13 counties in California, from Lassen County in the north to San Diego County in the south. The beetle is also widely distributed over much of the rest of the continental United States. This suggests it has the potential to become established over much or most of the state of California. Elms are widely planted in California. Therefore, Scolytus schevyrewi 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: Even though Scolytus schevyrewi has not been reported to attack trees other than a few species of Ulmus in the United States, it is also reported to attack trees in the Rosaceae in its native range. Therefore, it receives a Medium (2) 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: Scolytus schevyrewi is capable of sustained flight and it infests wood and wood products that could be moved (e.g. firewood). Therefore, it receives a Medium (2) 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: There does not appear to be any significant economic damage associated with schevyrewi in California, even though it is present over a large portion of the state. Elms are not a major timber tree, and the genus Prunus, which includes important fruit trees, does not appear to be affected in the United States. 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: Scolytus schevyrewi does not appear to have had a significant environmental impact in California, even though it is widely distributed in the State. Elms (Ulmus) are not native to California, and these are the only trees reported as being impacted by this beetle in the United States. Even though there do not appear to be many reports of this beetle damaging planted elms in the state, it is possible that this could occur during periods of drought. Therefore, it receives a Medium (2) in this category.

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

Environmental Impact: E

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: 2

– 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 Scolytus schevyrewi: Medium (10)**

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: Scolytus schevyrewi has already spread to at least 13 counties in California. The full extent of its distribution in the state is not known, and it is likely that its distribution will continue to expand. The current range represents a large enough area to consider the species fully established for the purposes of this pest rating proposal. It receives a High (-3) 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: Low (7)

Uncertainty:

The host range of S. schevyrewi in the United States was considered, for the purposes of this pest rating proposal, to be significantly narrower than what has been reported for this species’ native distribution. This was based on the available information. Because S. schevyrewi is already so widespread in the United States, it seemed that, if it had a broader host range in this country, it would have been reflected in the literature, especially considering how much attention this species has received. It is possible that S. schevyrewi does attack other genera and/or species of trees in the United States, but this has escaped attention.

Conclusion and Rating Justification:

When it was initially determined, in the mid-2000s, that Scolytus schevyrewi was present in the United States, there was much concern regarding the possible impact of this species on elms (and possibly on fruit trees as well). However, over a decade has elapsed and there is very little evidence of major economic or environmental impacts resulting from the species. It is apparently already widely distributed in California, and there is little evidence of significant impacts in the state. A “C” rating is justified.

References:

Campos-Bolaños, R., Atkinson, T.H., Cibrian-Tovar, D., and T. Méndez-Montiel. 2015. Primer registro de Scolytus schevyrewi Semenov 1902 (Coleoptera: Curculionidae: Scolytinae) en Mexico. Acta Zoologica Mexicana. 31(1): 146-148.

LaBonte, J.R. 2010. The banded elm bark beetle, Scolytus schevyrewi Semenov (Coleoptera, Curculionidae, Scolytinae) in North America; a taxonomic review and modifications to the Wood (1982) key to the species of Scolytus Geoffroy in North and Central America. ZooKeys. 56: 207-218.

Lee, J.C., Negrόn, J.F., McElwey, S.J., Witcosky, J.J., and S.J. Seybold. 2006. Pest Alert: Banded elm beetle – Scolytus schevyrewi. United States Department of Agriculture. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev2_026555.pdf

Negrόn, J.F., Witcosky, J.J., Cain, R.J., LaBonte, J.R., and Duerr II, D.A., McElwey, S.J., Lee, J.C., and S.J. Seybold. 2005. The banded elm bark beetle: A new threat to elms in North America. American Entomologist. 51(2): 84-94.

Seybold, S.J., Penrose, R.L., and A.D. Graves. 2016. Chapter 21: Invasive bark and ambrosia beetles in California Mediterranean forest ecosystems. In Paine, T.D. and F. Lieutier (Eds.), Insects and Diseases of Mediterranean Forest Systems (pp. 583-662). Springer.

Author:

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 Drive, Sacramento CA 95833, (916) 654-1211; plant.health[@]cdfa.ca.gov.

Comment Period:* CLOSED

1/16/2018 – 3/2/2018

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