Strangulate Weevil | Trochorhopalus strangulatus (Gyllenhal)

California Pest Rating for
Strangulate Weevil | Trochorhopalus strangulatus (Gyllenhal)
Pest Rating: A


Initiating Event:

Trochorhopalus strangulatus was recently reported to be established on the island of Hawaii (J. Matsunaga, pers. comm.).  The species is currently Q-rated, and a permanent pest rating proposal is required to support an official pest rating.

History & Status:

Background:  Trochorhopalus strangulatus is a weevil that is widely distributed in tropical sugarcane-growing areas.  Adults are reported to be 6-10 mm in length and are black with a coating of short, brown/gold setae (Corbett, 1932; Hustache, 1920; J. Matsunaga, pers. comm.).  This species is considered a pest of sugarcane.  The larvae bore into and feed in the stalks of the plant (Magarey et al., 2002).  However, some reports suggest it is of minor significance.  For example, it is reported to primarily attack sugar cane that is damaged or weak in Fiji (Imperial Bureau of Entomology, 1920).  The beetle has been reported to attack coconut palm; details on the damage inflicted are sparse, but one report suggests this beetle may provide conditions allowing other, more serious pests to attack trees (Corbett 1932).  This species was also reported to be associated with, and possibly damage bananas, although no further details were found (Harmer, 1912; Mararuai, 2010).  Lastly, this species is apparently often found associated with dead palm trees (J. Matsunaga, pers. comm.).

Worldwide Distribution:  Trochorhopalus strangulatus is known from islands in the Indian Ocean (Republic of Seychelles and the Mascarene Islands), Southeast Asia (Indonesia and Philippines), Papua New Guinea, Fiji, and Hawaii (Hustache, 1920; Magarey et al., 2002; J. Matsunaga, pers. comm.; Pemberton, 1963; Senterre et al., 2011; Symbiota Collections of Arthropods Network).  The native distribution is unknown, although one report states it is indigenous to the Seychelles (Senterre et al., 2011).  The distribution has presumably been expanded as a result of cultivation and transport of sugarcane in Southeast Asia and Pacific islands, which began thousands of years ago, and it is assumed that at least some localities represent introductions (Artschwager and Brandes, 1958).

Official Control: Trochorhopalus strangulatus is not known to be under official control anywhere.

California Distribution:  Trochorhopalus strangulatus is not known to occur in California.

California Interceptions:  Trochorhopalus strangulatus has not been intercepted in California.

The risk Trochorhopalus strangulatus would pose to California is evaluated below.

Consequences of Introduction:

1) Climate/Host Interaction: Trochorhopalus strangulatus has been reported to feed on sugarcane, banana, and palms. Of these, ornamental palms are the most obvious possible host plant in California, and they are present throughout much of the state.  Based on the current distribution of T. strangulatus (tropical areas), it appears unlikely that this species could become established in more than a very limited portion of California.  Therefore, this species receives a Low (1) 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: Trochorhopalus strangulatus is a pest of sugar cane, but has also been reported to attack coconut palm and bananas, which suggests at least three families of plants are fed upon. Unfortunately, details regarding feeding on these alternate host plants are lacking. Therefore, T. strangulatus 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: Trochorhopalus strangulatus presumably flies.  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: This weevil is a pest of sugarcane and it has also been reported to attack banana and palms.  California industries that could be affected by the establishment of this weevil include ornamental palms and sugarcane.  Ornamental palms are a $70 million industry in California, and damage (including lowering of yield) to palms in nurseries could result if T. strangulatus became established in California (Hoddle).  Sugarcane is either currently being grown in, or is planned to be grown in the Imperial Valley, where a sugarcane-based sugar and biofuels initiative is underway.  If this weevil became established in the Imperial Valley, which may not be likely given its apparent restriction to tropical areas, it could lower yield of sugarcane there.  An extensive sugarcane industry exists in the southeastern United States, and the climate in that region would likely be more favorable for the establishment of this pest.  The possibility of the spread of this pest to the southeastern United States (and impact on sugarcane and palms there), as well as other countries, could lead to a loss of markets for ornamental palms from California.  Therefore, T. strangulatus receives a Medium (2) in this category.

Economic Impact: A, C

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: If this weevil was introduced to California, it could potentially spread to groves of the only species of native California palm, Washingtonia filifera, although this is somewhat unlikely, considering that this weevil is apparently restricted to tropical areas and these palms occur in the desert. Therefore, it receives a Medium (2) in this category.

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

Environmental Impact: A

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: 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 Trochorhopalus strangulatus: 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: Trochorhopalus strangulatus 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: Medium (9)


There is a great deal of uncertainty regarding the feeding by this species on palms and banana.  A possibility that must be considered is that some of the feeding attributed to T. strangulatus could have been the result of another species misidentified as this one.  If this is the case, it means that the feeding habits of this species may be narrower than assumed in this rating proposal.  There is also uncertainty regarding the ability of this species to become established in California, apart from the issue of host plant.  This species is apparently restricted to areas with a tropical climate, and it appears unlikely to be able to become established in California, although parts of southern California could provide adequate conditions for it.  This beetle could become an established pest in parts of California.  A cautious approach has been taken here because of the ability of this species to attack living plants, as shown by its status as a sugar cane pest.

Conclusion and Rating Justification:

Trochorhopalus strangulatus is a tropical weevil that is not known to occur in California.  The beetle is a pest of sugarcane, and reports suggest it also attacks bananas and palms.  This species poses an economic and environmental risk to California.  For these reasons, an “A” rating is justified.


Artschwager, E. and E.W. Brandes.  1958.  Agriculture Handbook 122: Sugarcane (Saccharum officinarum L.); origin, classification, characteristics, and descriptions of representative clones.  United States Department of Agriculture.  United States Government Printing Office.  307 pp.

Corbett, G.H.  1932.  Insects of coconuts in Malaya.  Bulletin General Series (Straits Settlements & Federated Malay States Department of Agriculture).  10: 1-106.

Harmer, S.F.  1912.  Department of Zoology.  VI.  Economic zoology.  Return, British Museum.  1912: 163-167.

Hoddle, M.  Has the South American palm weevil, Rhynchophorus palmarum, established in southern California?  University of California, Riverside, Center for Invasive Species Research.

Accessed: November 17, 2017

Hustache, A.  1920.  Curculionides des iles Mascareignes.  Annales de la Société entomologique de France.  89: 113-203.

Imperial Bureau of Entomology.  1920.  Series A: Agricultural.  Review of Applied Entomology.  8: 1-40.

Magarey, R.C., Suma, S., Irawan, Kuniata, L.S., and P.G. Allsopp.  2002.  Sik na binatang bilong suka – Diseases and pests encountered during a survey of Saccharum germplasm ‘in the wild’ in Papua New Guinea.  Proceedings of the Australian Society of Sugar Cane Technology.  24: 219-227.

Mararuai, A.  2010.  Market access of Papua New Guinea bananas (Musa sp.) with particular respect to banana fly (Bactrocera musae (Tryon)) (Diptera: Tephritidae).  Ph.D. thesis.  School of Natural Resource Sciences, Queensland University of Technology, Brisbane, Australia.  192 pp.

Pemberton, C.E.  1963.  Important Pacific insect pests of sugar cane.  Pacific Science.  17(2): 251-252.

Senterre, B., Henriette, E., Chong-Seng, L., Beaver, K., Mougal, J., Vel, T., and J. Gerlach.  2011.  Seychelles key biodiversity areas.  Output 1: List of species of special concern.  Report of Consultancy, UNDP-GEF project, Ministry of Environment of Seychelles, Victoria, Seychelles.  67 pp.

Symbiota Collections of Arthropods Network.  Accessed 20 November 2017.


Kyle Beucke, 1220 N Street, Room 221, Sacramento, CA, 95814, 916-403-6741,[@]

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Jason Leathers, 2800 Gateway Oaks Drive, Sacramento CA 95833, (916) 654-1211;[@]

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1/11/2018 – 2/25/2018


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Pest Rating: A


Posted by ls