A Mealybug | Trionymus sasae (Kanda)

California Pest Rating for
Trionymus sasae (Kanda): a mealybug
Hemiptera: Pseudococcidae
Pest Rating: A


Initiating Event:

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

History & Status:

Background:  Trionymus sasae is only known to occur in Japan and it is associated with (and presumably feeds on) bamboo (García Morales et al., 2016).  The localities it is reported from in Japan have a subtropical climate (Kawai, 1980).  Other species of Trionymus are also associated with grasses (Poaceae), and some are pests of crop (e.g., barley and sugarcane) or ornamental (e.g., bamboo) plants (Alvarez, 2004; Jansen, 2009; Portilla and Cardona, 2004).

Worldwide Distribution:  Trionymus sasae is only known from Japan.  It was reportedly intercepted in California on bamboo from Oregon in 1995, so it is possible that this mealybug may be established in other areas (possibly Oregon), but if so, this has not been reported (Gill, 1995).  Alternatively, this bamboo may have originally been shipped from Japan.

Official Control: Trionymus sasae is not known to be under official control anywhere.

California Distribution:  Trionymus sasae is not known to be present in California.

California Interceptions:  Trionymus sasae has been intercepted on bamboo from Japan and Oregon (California Department of Food and Agriculture; Gill, 1995).

The risk Trionymus sasae would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: The areas in Japan where sasae is reported to occur have a subtropical climate. If this mealybug became established in California, it might be limited to warmer areas, for example, the southern coast.  Therefore, T. sasae receives a Medium (2) 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: Trionymus sasae has been associated with two genera of bamboo. Therefore, it receives a Low (1) 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: Trionymus sasae has been intercepted on bamboo, so it is apparently capable of being dispersed through shipment of plant material.  Bamboo is a popular plant and is presumably moved frequently throughout the state.  Therefore, sasae 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: Trionymus sasae lives on bamboo plants, which are popular ornamentals in California.  If this mealybug became established in California, it could attack bamboo plants in nurseries, impacting their health or at least detracting from their appearance and value.  This could increase production costs.  Therefore, sasae receives a Low (1) in this category.

Economic Impact:  B

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: There are many rare species in the family Poaceae in California (Calflora). If sasae became established in California, it could threaten some of these species.  This mealybug could also impact ornamental bamboo plantings, and this could trigger treatments.  Therefore, it receives a High (3) in this category.

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

Environmental Impact:  B, D, 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: 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 Trionymus sasae: Medium (9)

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: Trionymus sasae is not known to be present in 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 (9)


The known distribution of this species suggests it may be limited to warmer (subtropical) climates.  If so, it may not be capable of establishment in California, or its area of potential distribution in the state could be quite limited.  The potential of T. sasae to damage plants is also not known.  Little information is available on this species, so the pest significance of other Trionymus species was considered in this proposal.  The potential of this mealybug to impact native grasses in California would require that this species not be limited to bamboo.

Conclusion and Rating Justification:

Very little information is available regarding the biology of Trionymus sasae.  This mealybug is not known to be present in California and it attacks bamboo (an important ornamental plant in the state).  For these reasons, an “A” rating is justified.


Alvarez, J.M.  2004.  Trionymus haancheni McKenzie: A new pest of barley in Idaho.  Plant Management Network.  5 pp.

Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals, including the Consortium of California Herbaria.  Accessed March 30, 2017 http://www.calflora.org

California Department of Food and Agriculture.  Pest and damage record database.  Accessed March 30, 2018. https://pdr.cdfa.ca.gov/PDR/pdrmainmenu.aspx

García Morales, M., Denno, B.D., Miller, D.R., Miller, G.L., Ben-Dov, Y., and Hardy, N.B. 2016.  ScaleNet: A literature-based model of scale insect biology and systematics.  Accessed March 28, 2018  http://scalenet.info

Gill, R.J.  1995.  Exclusion.  California Plant Pest and Disease Report.  14: 8-12.

Jansen, M.  2009.  New and less observed scale insect species for the Dutch fauna (Hemiptera: Coccoidea).  Entomologische Berichten.  69: 162-168.

Kawai, S.  1980.  Scale Insects of Japan in Colors.  National Agricultural Education Association.  Tokyo.  455 pp.

Portilla, A.A.R. and Cardona, F.J.S.  2004.  Coccoidea de Colombia, con énfasis en las cochinillas harinosas (Hemiptera: Pseudococcidae).  Revista Facultad Nacional de Agronomía Medellín.  57: 2383-2412.

Symbiota Collections of Arthropods Network.  Accessed March 30, 2018. http://scan1.acis.ufl.edu


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

4/30/18 – 6/14/18


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Pest Rating: A


Posted by ls