California Pest Rating
Stenhomalus taiwanus Matsushita: Taiwan Slender Longhorned Beetle
Former Pest Rating: Not Rated
Current Pest Rating: A
In September 2016 the United States Department of Agriculture (USDA) New Pest Advisory Group (NPAG) released a report on Stenohomalus taiwanus that recommended that USDA establish a non-reportable/non-actionable port policy for the beetle in the continental United States. The beetle would remain actionable in Hawaii and the United States territories. Stephen Brown requested comments on this proposal.
History & Status:
Background: Stenhomalus taiwanus is a longhorned beetle that is only known to feed on stems and branches of two to five year old Zanthoxylum bungeanum (Sichuan pepper, Chinese pepper) and Zanthoxylum piperitum (Japanese prickly ash). Stenhomalus taiwanus has only one generation per year. Adult beetles emerge in summer and crawl on branches and leaves and may fly short distances. Larvae feed on the cortex and xylem of the tree where they overwinter and pupate in spring. The beetles may be transported long distances inside wood when infested plants or freshly cut stems and branches are moved.
Worldwide Distribution: Stenhomalus taiwanus is native to China, Japan and Taiwan. The only place it is known to have invaded is the southern United States, where it has been found in Georgia, Alabama, and Texas.
Official Control: Stenhomalus taiwanus is not known to be under official control in any other states or nations.
California Distribution: Stenhomalus taiwanus has never been found in the environment of California.
California Interceptions: Stenhomalus taiwanus has never been found in any regulatory situations in California.
The risk Stenhomalus taiwanus (Taiwan slender longhorned beetle) would pose to California is evaluated below.
Consequences of Introduction:
1) Climate/Host Interaction: There are no species of Zanthoxylum native to California and those plants are only occasionally cultivated here. If Stenhomalus taiwanus were to establish in California its distribution is likely to be very limited. It receives a Low (1) in this category.
Evaluate if the pest would have suitable hosts and climate to establish in California. Score:
– 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: Stenhomalus taiwanus is only known to feed on two species of plants in one genus. It receives a Low (1) in this category.
Evaluate the host range of the pest. Score:
– 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: Stenhomalus taiwanus only has one generation per year. It can be transported long distances when infested plants or fresh stems or branches are moved. It receives a Medium (2) in this category.
Evaluate the natural and artificial dispersal potential of the pest. Score:
– 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: Stenhomalus taiwanus has been present in the southern United States for more than five years and has not had any economic impacts. If it were to establish in California it is not likely to lower crop yields, increase crop production costs, disrupt markets, negatively change cultural practices, vector other organisms, injure animals, or interfere with water supplies. It receives a Low (1) in this category.
Evaluate the economic impact of the pest to California using the criteria below. Score:
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.
– 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: If Stenhomalus taiwanus were to establish in California it is not likely to lower biodiversity, disrupt natural communities, or change ecosystem processes. It is not expected to affect threatened or endangered species or disrupt critical habitats. It may trigger new treatment programs by residents who grow ornamental Zanthoxylum In California the beetle is not likely to significantly affect cultural practices, home/urban gardening, or ornamental plantings. Stenhomalus taiwanus receives a Medium (2) in this category.
Evaluate the environmental impact of the pest on California using the criteria below.
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.
Score the pest for Environmental Impact. Score:
– 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 Stenhomalus taiwanus (Taiwan Slender Longhorned Beetle): Low (7)
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: Stenhomalus taiwanus has never been found in California and receives a Not established (0) in this category.
Evaluate the known distribution in California. Only official records identified by a taxonomic expert and supported by voucher specimens deposited in natural history collections should be considered. Pest incursions that have been eradicated, are under eradication, or have been delimited with no further detections should not be included.
–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.
The final score is the consequences of introduction score minus the post entry distribution and survey information score: Low (7)
Stenhomalus taiwanus does not respond to any wood boring beetle lures and would not be found by CDFA’s exotic wood borer surveys. In the South it is most commonly collected at light traps. There have not been any recent comprehensive light trap surveys of California. Interception data and finds from other states indicate that the beetle has been moving into the United States in wood products from China. It is certain that some of these infested products also entered California. Furthermore, it is likely that Stenhomalus taiwanus has already entered California and remains undetected.
Although the beetle is only documented to feed on two species of Zanthoxylum, it is not known what plant(s) the beetle is using as a host in the United States. It has been intercepted on “willow” baskets from China. It is unknown what type of wood this actually was. If there has been host-switching there is potential for far-reaching forestry and environmental impacts.
Conclusion and Rating Justification:
If Stenhomalus taiwanus were to establish in California it is only expected to affect ornamental Zanthoxylum plants. However, there is significant uncertainty about what host plant(s) the beetle is using in the United States as its native hosts do not occur here except as occasional ornamentals. Until more information about the host range of this beetle is known or it is found in California an “A” rating is justified.
Newton, Leslie and David Bednar. 2016. NPAG Report Stenhomalus taiwanus Matsushita: Taiwan slender longhorn beetle. United States Department of Agriculture New Pest Advisory Group.
Jason Leathers, 1220 N Street, Sacramento, CA, 95814, (916) 654-1211, plant.health[@]cdfa.ca.gov.
Comment Period: CLOSED
10/13/2016 – 11/27/2016