1
Screening Aid
The sugar cane weevil, Rhabdoscelus obscurus (Boisduval), a native
of New Guinea, is a relatively large weevil that has spread to many
areas of the world, especially sugar cane growing regions of the
Pacific. The preferred host is sugar cane but this weevil has been
known to attack a large variety of plants, including banana and a
variety of palms, and infrequently corn. Larvae feed on stalks and
stems creating large tunnels, leading to plant death or loss of value
due to aesthetic damage in ornamental plants. This species has been
a pest in Hawaii since the 1860’s but has not been established in the
continental United States.
While there are several genera that are similar in appearance to
Rhabdoscelus , only a few are established in the U.S. Generic
separation is possible but difficult, and identification to species will be
difficult without representatives of each species to compare. Adults
are highly variable, ranging in size from 12-14 mm, colored reddish to
reddish-brown, and the pronotum often has a dark streak from apex
to base. Some species of Rhynchophorus have similar markings and
hosts, but can be differentiated by size. They typically measure 2-2.5
times longer and 3 times wider than R. obscurus. Separation from
other genera in the Dryophthoridae, the palm weevils, will be difficult
without a microscope but can be done by comparison of several key
characteristics. These genera include Cosmopolites , Metamasius ,
and Sphenophorus which share monocotyledonous hosts and whose
characters can be difficult to compare, and Scyphophorus which also
appears similar, but can be separated by their black color, larger size
and succulent host plants Agave and Yucca.
Visual inspection for the presence of larvae or larval damage is
effective, but traps using a combination of lures is recommended
for adults. This weevil has been transported by plant material into
several continents and little literature is available to separate species;
any specimen resembling R. obscurus should be reported. Basic
knowledge of adult Coleoptera morphology is necessary to screen for
R. obscurus suspects.
Hanna R. Royals 1, Todd M. Gilligan 1 and Charles F. Brodel 2
1) Identification Technology Program (ITP) / Colorado State University, USDA-APHIS-PPQ-Science & Technology (S&T), 2301 Research
Boulevard, Suite 108, Fort Collins, Colorado 80526 U.S.A. (emails: Hanna.H.Royals@aphis.usda.gov; Todd.M.Gilligan@aphis.usda.gov)
2) USDA-APHIS-PPQ, Miami Inspection Station, 6302 NW 36th St, Miami, FL 33122 U.S.A. (email: Charles.F.Brodel@aphis.usda.gov)
This CAPS (Cooperative Agricultural Pest Survey) screening aid produced for and distributed by:
USDA-APHIS-PPQ National Identification Services (NIS)
This and other identification resources are available at: http://caps.ceris.purdue.edu/taxonomic_services
Version 1.0
21 February
2017
Fig. 2: Adult female sugar cane weevil.
(Photo by Sarah McCaffrey).
Fig. 3: Adult female sugar cane weevil.
(Photo by Sarah McCaffrey).
Fig. 1: Rhabdoscelus obscurus larva.
(Photo by Caroline Harding).
Sugar Cane Weevil
Rhabdoscelus obscurus (Boisduval)
COLEOPTERA DRYOPHTHORIDAE
2
Sorting
Rhabdoscelus obscurus pheromone traps should be sorted initially for the presence of weevils of the
appropriate size, color, and shape. Traps that contain weevils meeting all of the following requirements should
be moved to Level 1 Screening (Page 3):
1) Weevils are approximately 12-14 mm (one-half inch) long (Fig. 4).
2) Weevils have an overall shape that is similar to the outline depicted in Fig. 4.
3) Weevils are reddish to red-brown, sometimes with a dark streak down midline of pronotum (Fig. 5).
4) Weevils have an elongated rostrum (Fig. 6).
Fig. 4: Outline and size of R. obscurus .
Actual size
Fig. 5: Dorsal aspect of R. obscurus. (Photo by Caroline Harding)
Fig. 6: Elongated rostrum of R. obscurus. (Photo by Caroline
Harding)
Sugar Cane Weevil
Rhabdoscelus obscurus (Boisduval)
COLEOPTERA DRYOPHTHORIDAE
3
Level 1 Screening
While most species similar in appearance to the sugar cane weevil are no\
t native to the United States, they
might be detected in commodity surveys as many have the same host plants, including sugar cane, palms, and
corn. Separation to family can be accomplished based on tarsal and antennal characteristics:
Tarsus: Dryophthoridae have flaps between tarsal claws (Fig. 7a) and Curculionidae do not (Fig. 7b):
Antenna : Dryophthoridae have a glabrous (lacking setae) first antennal club segment (Fig. 8a) and a scape
that surpasses the posterior margin of the eye (Fig. 8b). Curculionidae have a first antennal club segment that
is not glabrous (Fig. 8c) and a scape that does not surpass the posterior margin of the eye (Fig. 8d):
Related genera in the Dryophthoridae can be separated based on the shape of the scutellum. Rhabdoscelus
possesses a scutellum that is longer than it is wide, with the width equ\
al to or less than that of the sutural
interval, and with sides that are almost parallel (Fig. 9a). Cosmopolites has a scutellum that is sub-circular (Fig.
9b) while Metamasius , Sphenophorus, and Scyphophorus have a triangular scutellum (Fig 9c):
a b
Fig. 7: a) flaps between tarsal claws present in the Dryophthoridae and b) absence of flaps in
the Curculionidae
Dryophthoridae Curculionidae
Fig. 8: Differences in antennae of Dryophthoridae and Curculionidae (Photos by Charles Brodel
USDA-APHIS-PPQ)
Dryophthoridae Dryophthoridae Curculionidae Curculionidae
a b c d
a b c Rhabdoscelus Cosmopolites Metamasius, Sphenophorus,
and Scyphophorus
Fig. 9: Scutellum shapes differentiating some genera of the Dryophthoridae (Photos by Charles Brodel USDA-APHIS-PPQ)
Sugar Cane Weevil
Rhabdoscelus obscurus (Boisduval)
COLEOPTERA DRYOPHTHORIDAE
4
Key and References
Key to Sort and Screen Rhabdoscelus and Related Genera
1. Scutellum sub-circular, with length about equal to width; associated with
bananas ........................................................................................................................ Cosmopolites
1’. Scutellum almost parallel-sided, with length greater than width, width equal
to or less than that of sutural interval .......................................................... Rhabdoscelus suspect
1’’. Scutellum widest at base, triangular or tapering apically ................................................................. 2
2. Tarsal segment 3 with ventral pilosity restricted to anterolateral areas, area in middle
mostly glabrous; segment 3 not dilated in most species, about equal in width to segment 2,
dilated in a few species and wider than 2; associated with grasses and corn ............ Sphenophorus
2’. Tarsal segment 3 with ventral pilosity covering almost all of ventral surface except
near base at middle; segment 3 greatly dilated in most species compared to segment 2
but, if only slightly dilated, then longer than segment 2; associated with palms, sugar cane,
bananas, and bromeliads ............................................................................................... Metamasius
2’’. Tarsal segment 3 with ventral pilosity long, confined to apical margin as a continuous fringe,
ventral surface otherwise glabrous; segment 3 greatly dilated in both species compared to
segment 2; associated with Agave, Beaucarnea, and Yucca ..................................... Scyphophorus
Citation
Royals, H. R., T. M. Gilligan and C. F. Brodel. 2017. Screening aid: Sugar Cane Weevil, Rhabdoscelus obscurus
(Boisduval). Identification Technology Program (ITP), USDA-APHIS-PPQ-S&T, Fort Collins, CO. 4 pp.
References for more information on R. obscurus and non-targets
Anderson, R. S. 2002. Classification of the Nearctic Curculionidae. I. Dryophthorinae Schoenherr 1825, pp. 728-730. In R.
H. Arnett, Jr., M. C. Thomas, P. E. Skelley, and J. H. Frank, eds. CRC Press, Boca Raton, Florida.
Brodel, C. F. 2002. A Key to domestic and PPQ-Intercepted genera of Dryophthorinae (Coleoptera: Curculionidae).
Adapted from R. S. Anderson (2002).
Brodel, C. F. 2013. Dryophthoridae key by Zimmerman (1968) as modified by C. F. Brodel (2013).
DeBach P., and D. Rosen. 1991. Biological control by natural enemies 2nd ed. London: Cambridge University Press,
Cambridge, New York. p. 159.
Molet, T. 2013. CPHST Pest Datasheet for Rhabdoscelus obscurus . USDA-APHIS-PPQ-CPHST.
Zimmerman, E. C. 1968. Rhynchophorinae of southeastern Polynesia (Coleoptera: Curculionidae). Pacific Insects 10(1):
47-77.
Acknowledgments
We would like to thank USDA-APHIS-PPQ National Identification Services and the USDA-APHIS-PPQ-S&T Identification
Technology Program for support of this work, and Jim E. Zablotny (Identifier, USDA APHIS PPQ) for their review of this
screening aid. Funding for this project was provided to H. Royals through section 10007 of the 2014 Farm Bill.
Sugar Cane Weevil
Rhabdoscelus obscurus (Boisduval)
COLEOPTERA DRYOPHTHORIDAE
