New Guinea Sugarcane Weevil | Rhabdoscelus obscurus (Boisduval)

California Pest Rating  for 
(New Guinea Sugarcane Weevil) | Rhabdoscelus obscurus (Boisduval) 
Coleoptera: Curculionidae
Pest Rating: A


Initiating Event:

This weevil was recently intercepted on cut ginger flowers from Hawaii (190P06619908).  The species is currently Q-rated, and a permanent pest rating proposal is required to support an official pest rating.

History & Status:

Background: Adult Rhabdoscelus obscurus are 12-14 mm in length and reddish-brown with a longitudinal black stripe on the pronotum.  The larvae are white, legless grubs with a dark head capsule and are approximately 15 mm in length (Molet, 2013).  This weevil is a pest of sugarcane and palms.  The larvae tunnel and feed inside stalks, which leads to stalk breakage.  Prior to pupating, they build a fibrous cocoon.  This species appears to currently be restricted to tropical and subtropical areas.

Worldwide Distribution: Rhabdoscelus obscurus is native to New Guinea and has been introduced to much of the tropical western Pacific, including Indonesia, Japan, Malaysia, Taiwan, and numerous Pacific islands (Beardsley et al., 1995; Molet, 2013; Zimmerman, 1968).  It has also been introduced to Australia (Reddy et al., 2012).  In the United States, it has been present in Hawaii since the mid-1800s (Waggy and Beardsley, 1974).  The species is not known to occur in the continental United States.

Official Control: Rhabdoscelus obscurus is listed as a quarantine pest by the EPPO, and is considered reportable by USDA-APHIS-PPQ (EPPO, 2017).  The species has been controlled in Hawaii through the introduction of a tachinid fly parasitoid (Waggy and Beardsley, 1974; Beardsley et al., 1995).

California Distribution: Rhabdoscelus obscurus is not known to be present in California.

California Interceptions: Rhabdoscelus obscurus has been intercepted in California twice, once on cut ginger flowers from Hawaii in 2017 and once on a shipment of pineapple from Hawaii in 2004 (CDFA Pest and Damage Report Database, 2017).

The risk Rhabdoscelus obscurus would pose to California is evaluated below.

Consequences of Introduction:

1)  Climate/Host Interaction: Rhabdoscelus obscurus is currently restricted to tropical and subtropical areas.  It could become established in a limited portion of southern California.  Therefore, it 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: Rhabdoscelus obscurus is a major pest of sugarcane and also feeds on other monocots, including numerous palms as well as bananas, some grasses, and corn (Beardsley et al., 1995; EPPO, 2017; Molet, 2013).  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 Dispersal Potential: Rhabdoscelus obscurus flies and it is capable of being introduced to new locations; much of its present distribution is due to such introductions.  The species has been intercepted 19 times (as of 2012) at United States ports of entry on infested plant material, so can be artificially dispersed that way (Molet, 2013).  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: Rhabdoscelus obscurus is a significant pest of sugarcane and palms.  The species causes significant mortality of palms in the Pacific, and it is a palm nursery pest in Australia (Reddy et al., 2012).  If established in California, it could impact palm nurseries, lowering yield.  Ornamental palms are a $70 million industry in California (Hoddle).  The other California industry that could be impacted by this pest is sugarcane.  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 R. obscurus was able to become established in the Imperial Valley, which may not be likely, 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 R. obscurus to the southeastern United States and other countries could lead to a loss of markets for ornamental palms from California.  Rhabdoscelus obscurus 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 R. obscurus became established in California, it could impact ornamental plantings of palms, which are an important part of the California landscape.  The species could also potentially spread to groves of the only species of palm native to California, Washingtonia filifera, although this is somewhat unlikely, considering that this weevil is restricted to wet tropical and sub-tropical climates and these palms occur in the desert.  Therefore, Rhabdoscelus obscurus receives a High (3) in this category.

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

Environmental Impact:  A, 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 Rhabdoscelus obscurus: Medium (11)

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: Rhabdoscelus obscurus is not known to occur in California.  It 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.

Final Score:

7)  The final score is the consequences of introduction score minus the post entry distribution and survey information score: Medium (11)


Rhabdoscelus obscurus clearly has the potential to become established in new areas and cause great harm to sugarcane and palms, because it has already done so in much of the Pacific.  However, it is possible that the climate in California will not be suitable for the establishment of this species.

Conclusion and Rating Justification:

Rhabdoscelus obscurus is a weevil pest of sugarcane and palms that is not known to be present in California.  It could become established in restricted areas of California.  If this happened, it could cause damage to ornamental palms (and possibly the one native species).  The planned sugarcane-based industries in the Imperial Valley would also be threatened.  An “A” rating is justified.


Beardsley, J. W., Leeper, J. R., Topham, M., and Waggy, S. L.  1995.  New Guinea sugarcane weevil.  pp. 183-184 in (Nechols, J.R., Andres, L.A., Beardsley, J.W., Goeden, R.D., and Jackson, C.G., Biological control in the western United States.  University of California Division of Agriculture and Natural Resources, Oakland, California.

CDFA Pest and Damage Report Database.  2017.  Rhabdoscelus obscurus.  Plant Health and Pest Prevention Services. CA Department of Food and Agriculture.  Accessed November 28, 2017:

EPPO.  2017.  EPPO Global Database (available online).  Accessed September 7, 2017:

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:

Molet, T.  2013.  CPHST pest datasheet for Rhabdoscelus obscurus.  USDA-APHIS-PPQ-CPHST.  Accessed September 7, 2017:

Reddy, G. V. P., Shi, P., Mann, C. R., Mantanona, D. M. H., and Dong, Z.  2012.  Can a semiochemical-based trapping method diminish damage level caused by Rhabdoscelus obscurus (Coleoptera: Curculionidae)?  Annals of the Entomological Society of America 105:693-700.

Symbiota Collections of Arthropods Network.  Accessed November 28, 2017:

Waggy, S. L. and Beardsley, J. W.  1974.  Biological studies on two sibling species of Lixophaga (Diptera: Tachinidae), parasites of the New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval).  Proceedings of the Hawaiian Entomological Society 21:485-494.

Zimmerman, E. C.  1968.  Rhynchophorinae of southeastern Polynesia.  Pacific Insects 10:47-77.


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,[@]

Comment Period:* CLOSED

7/3/18 – 8/17/18


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Pest Rating: A


Posted by ls