Ambrosia Beetle | Euwallacea similis (Ferrari)

California Pest Rating for
Ambrosia Beetle | Euwallacea similis (Ferrari)
Coleoptera: Curculionidae: Scolytinae
Pest Rating: A



Initiating Event:

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

History & Status:

Background:  Adult female Euwallacea similis measure approximately 2.5 mm in length.  Males are smaller, approximately 1.8 mm long.  Body color is reddish-brown (Kalshoven, 1964).  Like other ambrosia beetles, this species excavates galleries in wood.  Ambrosia fungus becomes established in these galleries and provides the primary food source for the larvae.  This beetle is common in stressed and dead (including cut) trees in the tropics; it is not known to attack healthy trees (Browne, 1961; CABI, 2018; Kalshoven, 1964; Maiti and Saha, 1986).  Some ambrosia beetles directly damage cut timber via tunneling behavior and stain the wood with the ambrosia fungus.  Browne (1961) reported E. similis to attack cut trees, and Sittichaya and Beaver (2009) reported damage to sawn rubber tree wood.  Reported host plants of E. similis include 62 genera in 29 families (Kalshoven, 1964; Maiti and Saha, 1986; Wood and Bright, 1992).

Worldwide Distribution:  Ambrosia beetles are easily introduced to new localities via movement of infested wood.  This is likely the reason that the native distribution of E. similis is uncertain.  However, this beetle is thought to be native to Asia and the Pacific from Pakistan to the Solomon Islands (CABI, 2017).  Countries included in the presumed native distribution are Australia, Bangladesh, Bhutan, Cambodia, China, India, Indonesia, Japan, Malaysia, Myanmar, Nepal, Pakistan, Papua New Guinea, Philippines, Singapore, Sri Lanka, Taiwan, Thailand, and Vietnam (CABI, 2017; Mathew et al., 2005; Rabaglia et al., 2006; Schedle, 1968).  This beetle has been introduced to Cameroon, Egypt, Jordan, Kenya, Mauritania, Mauritius, Pacific Islands (including Christmas Island, Cocos Island, Fiji, French Polynesia, Guam, Kiribati, Marshall Islands, Federated States of Micronesia, New Caledonia, Northern Mariana Islands, Palau, and Samoa), Seychelles, South Africa, Tanzania, and the United States (Florida, Mississippi, and Texas) (Atkinson, 2018; CABI, 2017; K. Fairbanks, pers. comm.; Halbert, 2012; Halbert, 2014; Symbiota Collections of Arthropods Network).

Official Control: Euwallacea similis is a Controlled Pest in the Republic of Korea (Food and Agriculture Organization of the United Nations, 2016).

California Distribution:  Euwallacea similis is not known to occur in California (Symbiota Collections of Arthropods Network).

California Interceptions:  Euwallacea similis was intercepted on Limnophila chinensis cuttings from Hawaii in 2004 (CDFA Pest and Damage Report Database, 2018).

The risk Euwallacea similis would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Euwallacea similis is apparently restricted to tropical and subtropical areas, so climate could limit the distribution of this species in California. This beetle has been reported to utilize numerous species of trees in at least 29 families.  Most or all of California has trees from many of these families (Calflora, 2018).  Fungus, which is the food of all life stages of similis, is carried by the adult female and would therefore be introduced to any new places this beetle inhabits.  Therefore, Euwallacea similis 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: Euwallacea similis feeds on fungi in galleries that are excavated in trees. Trees in at least 29 families are used by this beetle.  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 Reproductive and Dispersal Potential: There is evidence suggesting that ambrosia beetles that have brother-sister mating, which is the case with similis, have an enhanced ability to disperse and colonize new areas.  A single female, whether fertilized or not, can start a new population.  If she is unfertilized, she can produce sons from unfertilized eggs and mate with them.  Euwallacea similis flies (specimens have been caught with funnel traps).  Rapid, long-distance dispersal could result from movement of infested firewood (Wood, 2007).  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: Euwallacea similis is reported to only attack stressed, dead, or dying trees; it is not reported to attack healthy trees (CABI, Kalshoven, 1964).  However, this species is reported to attack sawn timber, and it could therefore damage cut timber through gallery excavation and staining caused by the ambrosia fungus (Sittichaya and Beaver, 2009).  Avoidance of this damage could require a change in normal cultural practices.  There is also the chance that this beetle could vector a plant-pathogenic fungus to economically-important trees.  Therefore, it receives a Medium  (2) in this category.

Economic Impact:  D, 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: Euwallacea similis has not been reported to have an environmental impact anywhere it has been introduced. This does not mean that this beetle is not capable of having an impact in California.  Ambrosia beetles are less constrained than other scolytines 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.

Score the pest for Environmental Impact. Score:

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 Euwallacea similis: 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: Euwallacea similis 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:

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


There is a lack of evidence that E. similis is having economic or environmental impacts in the United States, where this species is apparently established in Florida, Mississippi, and Texas.  Therefore, the possible economic impacts considered in this proposal may be pessimistic.  There do not appear to be any reports of E. similis having an environmental impact anywhere in the world.  However, this may simply reflect a lack of research rather than an actual lack of impact.  Ambrosia beetles depend on ambrosia fungi, which have their own environmental requirements, including temperature and humidity (Kirisits, 2007).  The climate of California may not be suitable for these fungi, which may preclude the establishment of E. similis.  Drought-stressed trees could be more susceptible to attack by ambrosia beetles, including E. similis.  Therefore, an increase in drought resulting from climate change could make California’s trees more vulnerable to this and other ambrosia beetles.  There is also uncertainty regarding the possibility of E. similis (and other ambrosia beetles) interacting with plant-pathogenic fungal species that are already present in California.

Conclusion and Rating Justification:

There is no evidence that Euwallacea similis causes economic or environmental damage anywhere it is known to have been introduced.  However, it seems that a cautious approach is best with possible forest pests.  The behavior of this beetle may be different in the environments of California.  At least one introduced ambrosia beetle, Xyleborus glabratus, has become a serious pest species in the southeastern United States; it is having a significant impact on the environment as well as threatening the avocado industry.  The fungus symbiosis with ambrosia beetles raises special concerns, because the beetle could bring with it possibly pathogenic fungi new to California, or it could develop a new relationship with fungi already here.  For these reasons, an “A” rating is justified.


Atkinson, T. H.  2018.  Bark and ambrosia beetles.  Accessed: February 16, 2018:

Browne, F. G.  1961.  The biology of Malayan Scolytidae and Platypodidae.  Malayan Forest Records 22:1-255.

CABI.  2017.  Invasive Species Compendium.  Accessed February 2, 2018:

Calflora.  2018.  Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals.  Accessed February 6, 2018:

CDFA Pest and Damage Report Database.  2018.  Euwallacea similis.  Plant Health and Pest Prevention Services. CA Department of Food and Agriculture.  Accessed April 25, 2018:

Food and Agriculture Organization of the United Nations.  2016.  List of quarantine pests in Korea.  Accessed February 2, 2018:

Halbert, S. E.  2012.  Entomology section.  Tri-ology 51:7-9.

Halbert, S. E.  2014.  Entomology section.  Tri-ology 53: 6-9.

Kalshoven, L. G. E.  1964.  The occurrence of Xyleborus perforans (Woll.) and X. similis in Java (Coleoptera, Scolytidae).  Beaufortia 11:131-142.

Kirisits, T.  2007.  Fungal associates of European bark beetles with special emphasis on the ophiostomatoid fungi.  pp. 181-235 in Lieutier, F., Day, K.R., Battisti, A., Grégoire, J-C., and H.F. Evans, H.F. (eds.), Bark and wood boring insects in living trees in Europe, a synthesis.  Springer.

Maiti, P. K. and Saha, N.  1986.  A contribution to the knowledge of the bark and timber beetles (Scolytidae: Coleoptera) of the islands of Andaman and Nicobar, India.  Records of the Zoological Survey of India Miscellaneous Publication Occasional Paper 86:1-182.

Mathew, G., Shamsudeen, R. S. M., and Chandran, R.  2005.  Insect fauna of Peechi-Vazhani Wildlife Sanctuary, Kerala, India.  ZOO’s Print Journal 20:1955-1960.

Rabaglia, R. J., Dole, S. A., and Cognato, A. I.  2006.  Review of American Xyleborina (Coleoptera: Curculionidae: Scolytinae) occurring north of Mexico, with an illustrated key.  Annals of the Entomological Society of America 99:1034-1056.

Schedl, K. E.  1968.  On some Scolytidae and Platypodidae of economic importance from the territory of Papua and New Guinea.  Pacific Insects 10:261-270.

Sittichaya, W. and Beaver, R.  2009.  Rubberwood-destroying beetles in the eastern and gulf areas of Thailand (Coleoptera: Bostrichidae, Curculionidae: Scolytinae and Platypodinae).  Songklanakarin Journal of Science and Technology 31:381-387.

Symbiota Collections of Arthropods Network.  Accessed February 16, 2018:

Wood, S. L.  2007.  Bark and ambrosia beetles of South America.  Brigham Young University, Provo, Utah.


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,[@]

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Pest Rating: A


Posted by ls