Diagnostic Protocol Rice water weevil Lissorhoptrus oryzophilus Information prepared by Rolf Oberprierler & Ben Boyd CSIRO Entomology, Canberra ACT, 2601 December 2004 (reviewed 2008) The scientific and technical content of this document is current to the date published and all efforts were made to obtain relevant and published information on the pest. New information will be included as it becomes available, or when the document is reviewed. The material contained in this publication is produced for general information only. It is not intended as professional advice on any particular matter. No person should act or fail to act on the basis of any material contained in this publication without first obtaining specific, independent professional advice. Plant Health Australia and all persons acting for Plant Health Australia in preparing this publication, expressly disclaim all and any liability to any persons in respect of anything done by any such person in reliance, whether in whole or in part, on this publication. The views expressed in this publication are not necessarily those of Plant Health Australia. Introduction (Coleoptera: Curculionidae: Erirhininae) The name “Rice Water Weevil” applies both to a particular species of weevil, Lissorhoptrus oryzophilus Kuschel, which is one of the most serious pests of cultivated rice (Oryza sativa) in the world, and to a larger group of similar weevils that live on aquatic grasses in the New World and are real or potential rice pests as well. While this protocol deals specifically with L. oryzophilus, the diagnostic key makes provision also for recognising other relevant rice water weevils at group and genus level, so as to facilitate their detection at ports of entry in Australia and the taking of appropriate steps to prevent them from establishing in the country. Rice Water Weevil (RWW) belongs to the subfamily Erirhininae, a small cosmopolitan group of weevils generally associated with monocotyledonous plants in aquatic and semi-aquatic habitats. The definition, composition and classification of the Erirhininae are poorly understood, and considerable taxonomic expertise is often required to recognise these weevils. The group is not very diverse in Australia but includes a few large (but poorly known) genera, such as Echinocnemus and Aonychus. The taxonomy of the Australian erirhinine fauna was revised by Zimmerman (1993), whose work should be consulted for details about the various species and their distribution. Echinocnemus occurs Want more info? If you would like more information, or to download a copy of the Industry Biosecurity Plan, visit www.planthealthaustralia.com.au, email [email protected] or phone (02) 6260 4322. PLANT HEALTH AUSTRALIA | Rice Industry Biosecurity Plan 2009 on aquatic grasses in the Old World and includes rice pests in Africa (E. gemellus Marshall, E. obscurus Hustache), India (E. oryzae Marshall) and Japan (E. bipunctatus Roelofs, E. squameus (Billberg)), but the biology and hosts of the Australian species are not recorded. In Africa a similar weevil, Afroryzophilus djibai Lyal, damages rice in Senegal (Lyal 1992). Along with other weevils injurious to rice, Echinocnemus and Afroryzophilus are referred to as “rice weevils”, rather than “rice water weevils”. In the New World, a particular group of Erirhininae, the tribe Stenopelmini (sometimes incorrectly referred to as Hydronomini, e.g. Zimmerman 1993), is very diverse and important, including both serious agricultural pests and highly successful weed biocontrol agents. These weevils are characterised by having 6 (rather than 7) segments in the antennal funicle (see diagnostic key) and mostly by their body being covered by a more or less continuous, smooth layer of fused (agglutinated) scales. In Australia there are three native genera currently classified in Stenopelmini (Athor, Baeosomus, Niphobolus), and four South American species (Cyrtobagous salviniae Calder & Sands, Neochetina bruchi Hustache, N. eichhorniae Warner, Neohydronomus affinis Hustache) introduced as biocontrol agents of invasive aquatic weeds. None of these species are known to attack rice. Within the Stenopelmini, a group of eight New World genera (Bagoidellus, Bagoidus, Helodytes, Hydrotimetes, Ilyodytes, Lissorhoptrus, Neobagoidus, Oryzophagus) are collectively known as “rice water weevils”. These genera are classified in a subtribe Lissorhoptrina and characterised by an asymmetrical antennal club, narrow tarsi and long swimming hairs on the middle tibiae (see Hix et al. 2000 for details of swimming behaviour). As far as their hosts are known, most of them feed on aquatic grasses, with Lissorhoptrus and Oryzophagus specifically recorded also from rice. No native Lissorhoptrina occur in Australia, and no exotic species are known to have been introduced. Lissorhoptrus includes the “rice water weevils” in the strict sense. The genus occurs in both North and South America and currently comprises 19 species, but several undescribed ones are known and a revision of the North American species is in progress by C. W. O‟Brien. At least eight species are thus far recorded as attacking rice: L. oryzophilus Kuschel and L. simplex (Say) in North America, L. erratilis Kuschel, L. isthmicus Kuschel, L. kuscheli O‟Brien and L. persimilis O‟Brien in Central America, and L. bosqi Kuschel and L. tibialis (Hustache) in South America. Species catalogues of Lissorhoptrus are provided by O‟Brien & Wibmer (1982) Wibmer & O‟Brien (1986), O‟Brien & Anderson (1996) and Morrone & O‟Brien (1999). Lissorhoptrus oryzophilus is the most serious of these rice pests and has spread to other rice-growing areas of the world, in particular Central America and eastern Asia (India, China, Korea, Japan). Its distinction from other Lissorhoptrus species is difficult and relies on subtle differences in the genitalia and metatibial spines of the males. Identification keys to Lissorhoptrus species have been constructed by Kuschel (1952) and O‟Brien (1996), but neither is comprehensive and able to distinguish L. oryzophilus and other rice pests from various undescribed species of the genus that have become known since. Lissorhoptrus oryzophilus had been confused with the very similar L. simplex in the earlier literature, until Kuschel (1952) recognised and described it as a distinct species. References to L. simplex prior to 1952 mostly relate to L. oryzophilus. Diagnostic protocol: Rice water weevil | PAGE 2 PLANT HEALTH AUSTRALIA | Rice Industry Biosecurity Plan 2009 For information about distribution, hosts, biology and symptoms of damage of RWW, see Pest Risk Analysis by Stevens (2004) (Rice Industry Biosecurity Plan - Appendix 1) and http://www.ipm.ucdavis.edu/PMG/r682300511.html. For technical terms relating to diagnostic characters, see Glossary. Diagnostic images of RWW Figures 1-6: adult Lissorhoptrus oryzophilus Kuschel; dorsal, lateral and ventral view, abdominal ventrites, mesotibial swimming hairs, tridentate metatibial mucro of male. Images of the larva, pupal cocoon and larval feeding scars on rice leaves are available at http://www.ipm.ucdavis.edu/PMG/r682300511.html. Organisms that occur in Australia with which RWW might be confused Although RWW is readily distinguishable from all other weevils in Australia by its flattened, curved middle tibiae fringed with long swimming hairs, these hairs are easily abraded, making identification of RWW difficult when specimens are damaged in this or other features, or generally in poor condition. No identification keys are available to all Australian weevils (ca. 4200 described species), but since RWW lives in aquatic habitats, its distinction is only relevant from a relatively small number of weevils that live in similar environments in Australia. Four groups of such weevils occur in Australia: Listroderini (Figures 7 -14) This group includes three described native genera, Anorthorhinus, Ethemaia and Steriphus, and two introduced species of Listronotus, L. bonariensis (Kuschel) and L. setosipennis (Hustache), the former of which mines in stems of various grasses and the latter is employed in the biocontrol of the pasture weed Parthenium hysterophorus. All these Australian Listroderini are distinguishable from RWW by having several fine longitudinal carinae (keels) on the rostrum, the scales on the pronotum and elytra separate, not agglutinated, and the ventral side covered with setae only, not scales (at most a few scales laterally). Their larvae feed on the roots, stems and leaves of a variety of plants but are not aquatic (lack spine-like spiracles for tapping air from submerged plant parts, see May 1994). Bagoini (Figures 15-16) This small weevil group includes only one genus in Australia, Bagous, which was recently taxonomically revised (O‟Brien & Askevold 1992) and currently comprises 27 described species in Australia. Its species are superficially very similar to RWW, with a similar coating of agglutinated scales, but can readily be distinguished by the broad prosternal canal in front of the fore coxae, into Diagnostic protocol: Rice water weevil | PAGE 3 PLANT HEALTH AUSTRALIA | Rice Industry Biosecurity Plan 2009 which the rostrum is retracted. Other differences include the setose antennal club, a 7-segmented antennal funicle (often seemingly 6-segmented, the apical segment being enlarged and closely fitted to the club), the elytra having a prominent protuberance on the declivity, and the middle and hind tibiae being cylindrical and sharply bent inwards at the apex. Bagous larvae feed on various aquatic