Bull. Ir. biogeog. Soc. No. 31 (2007) FINDING JEWELS AMONGST THE REEDS: A REVIEW OF THE IRISH DONACIINE BEETLES (COLEOPTERA: CHRYSOMELIDAE) Brian Nelson Department of Zoology, National Museums Northern Ireland, Cultra, Holywood, BT18 0EU, Northern Ireland. e-mail: [email protected] John Walsh 26 Verbena Grove, Dublin 13, Ireland. Garth Foster Balfour-Browne Club, 3 Eglinton Terrace, Ayr, KA7 1JJ, Scotland. Abstract The donaciine beetles are a colourful group of beetles which feed on aquatic and wetland plants. The Irish fauna is reviewed and species accounts for each of the Irish species are provided, describing the history and habitat. The provisional distribution is shown on a map which distinguishes between post- and pre-1980 records. The Irish checklist is updated with one species added, Donacia sparganii and one, Donacia dentata, removed. A full bibliography of references is included. Introduction The donaciine beetles (sometimes referred to as reed beetles) are a distinctive and highly attractive group of insects within the family Chrysomelidae. They are phytophagous, feeding especially on freshwater monocotyledonous plants (Menzies and Cox, 1996). The larvae feed on the submerged parts of the plants, breathing by tapping into the intracellular spaces of the host plants. The adults usually feed on the leaves of the same host plant (Menzies and Cox, 1996), but also on pollen of this or other plants, particularly Yellow Iris Iris pseudacorus. Pupation within cocoons also occurs underwater, so the species are more aquatic than many of the species -117- Bull. Ir. biogeog. Soc. No. 31 (2007) in the more recognised water beetle families. Donaciine beetles occur worldwide and approximately 160 species have been described (Askevold, 1990). The web site of Fauna Europaea lists 33 species of Donacia, 3 Macroplea and 10 Plateumaris as present in Europe. In Britain and Ireland, the fauna comprises 15 Donacia, 2 Macroplea and 4 Plateumaris species (Menzies and Cox, 1996). In this paper we provide the first comprehensive account of the Irish fauna, which includes a review of the literature records, a listing of all the unpublished records known to us and distribution maps for all the species. We have recorded reed beetles in Ireland since 1988 which has generated most of the records presented here. Unpublished records have also been obtained from other entomologists and from examination of museum collections. One of the reasons for our interest in this group of beetles is that they appear to be sensitive indicators of the habitat quality in freshwaters. In Britain, several species have shown severe declines, although the reasons are unclear (Menzies and Cox, 1996). We hope the baseline data presented here will allow future workers to assess changes in the status of the Irish species as well as providing an incentive to others to record these attractive aquatic beetles. Recognisable fragments of donaciine beetles, particularly Plateumaris, are regularly to be seen in peat deposits, opening up the possibility of tracing the arrival of reed beetles over time in conjunction with studies of mitochondrial DNA: this has recently been achieved in Japan (Sota and Hayashi, 2007). Taxonomy The classification of the subfamily Donaciinae was reviewed by Askevold (1990) and this proposed three tribes within the subfamily — the Donaciini, Plateumarini and Hemoniini, although the first two were recognised as being paraphyletic. Representatives of all three tribes are found in Ireland. The tribe Donaciini include the highly-coloured species, the vast majority of which are placed in Donacia Fabricius. Askevold (1990) reviewed the subgenera of Donacia, and raised one, Donaciella Reitter to generic status. This has been accepted by some (e.g. Warchaowski, 2003), but not others (Menzies and Cox, 1996). Donaciella as defined in Askevold (1990) contains three European species, including cinerea and clavipes on the Irish -118- Bull. Ir. biogeog. Soc. No. 31 (2007) list. The subgenus Donacia contains only crassipes amongst the European species; all the other European species are included in Donaciomima Medvedev. These changes are not universally accepted and we have been conservative here and followed the nomenclature and taxonomy of the latest Irish checklist (Anderson et al., 1997). All the species of the tribe Plateumarini, with the exception of one Nearctic species, are placed in Plateumaris Thomson by Askevold (1990). The European Plateumaris are stockier insects than most donaciines with rounded elytra, prominent metafemoral teeth and inverted elytral sutures (Menzies and Cox, 1996). The separate status of Plateumaris discolor and P. sericea is disputed by some. Askevold (1991) synonymised the two but they are considered separate species in the latest British and Irish checklists and by Menzies and Cox (1996). The Hemoniini are quite different from the other species as they are non-metallic beetles with a prominent spine on the outer apical angle of each elytron. The underside is not densely hairy as in the other species. The three European species in this tribe are included in the genus Macroplea Samouelle. They are the most aquatic of the group, the adults and larvae living submerged on their host plants, species of Haloragaceae (milfoils), Potamogetonaceae (pondweeds) and Zosteraceae (eel-grasses). Identification With the exception of the Macroplea species mentioned above, initial identification of a beetle as a donaciine is relatively straightforward as they are robust, elongate beetles with long antennae, densely hairy undersides and, in most species, bright, often metallic, elytra. The thorax and elytra are punctate and sculptured which provides useful microscopic characters. The legs are robust with large, clawed tarsi that give the beetle excellent grip on the leaves of their foodplants. A key to the tribes and genera of Palaearctic donaciines is provided by Askevold (1990) and Warchaowski (2003). Species identification is more problematic. The colour of the adults of some species is prone to intraspecific variability so this most obvious and attractive feature of the adults has to be used with care. The structure and size of the two sexes differ in most species and there is also variation in appearance within and between sites. As with all -119- Bull. Ir. biogeog. Soc. No. 31 (2007) insect identification, access to reliably-named vouchers is of great assistance in making correct determinations and to appreciate the characteristics of each species. This should be complemented with field study of the species. The most up-to-date keys in English are provided by Menzies and Cox (1996), Warchaowski (2003) and Biekowski (2004). The keys in Fowler (1890) and Joy (1932) both suffer from poor discrimination of characters, inadequate illustrations and outdated taxonomy. Mohr’s key (1966), in German, includes illustrations of all the male genitalia, providing critical characters for discriminating some of our species. The only way to judge the sex of adults externally is on size. The males are generally smaller and slimmer which is usually obvious in a sample containing both sexes, but can be difficult to judge on a single individual. Adults may reveal their sex and species after capture as they tend to be promiscuous even within the confines of a collecting tube. Additional identification characters and photographs of the pronotal sculpturing are given in Bratton and Greenwood (1997). Colour illustrations or photographs of the species appear in a number of publications including Fowler (1890), Menzies and Cox (1996) and du Chatenet (2002) and on web pages (http://culex.biol.uni.wroc.pl/cassidae/European%20Chrysomelidae/donaciinae.htm or http: //www.coleopterist.org.uk). It must be recognised that photographs, whilst useful in giving a general impression of the species, rarely convey accurately the colour of the insects due to the high reflectivity of the elytra. Biology Donaciines are phytophagous beetles intimately linked with aquatic and wetland plants so are usually found close to open water. The larvae, pupae and cocooned adults of all of the species are aquatic. The aquatic stages are found around the roots of the host plants and these breathe by tapping into the intracellular airspaces of the host plants (Menzies and Cox, 1996). The adult phase is the most terrestrial, but even adults will rarely stray far from water. At individual sites the adults of the Donacia species are found most easily on plants growing in the swamp zones, but occasionally they may be seen on flowers in adjacent habitats. The common Irish Plateumaris are less closely tied to open water and frequently occur on bogs and fens. -120- Bull. Ir. biogeog. Soc. No. 31 (2007) Whilst the adults of the Donacia and Plateumaris species emerge from the water, adult Macroplea remain in the water. Collecting, field observation and recording A useful review of techniques for collecting donaciines is given in Menzies and Cox (1996). The adult is the easiest stage to find and collect. In general the most effective techniques are sweeping stands of aquatic plants and hand searching. Sweeping is a rather hit-or-miss technique and it can be impossible to associate the species with a foodplant where vegetation is mixed. Hand searching is much less indiscriminate and more time-consuming, but it allows the species to be associated directly with a host plant. To collect the aquatic species and those that live on floating leaves requires the use of pond nets. Comments applicable to individual species are given in the species accounts. Finding larvae and cocoons is reportedly much more difficult, as it involves searching amongst the roots of host plants. This necessitates the removal of whole plants from the habitat which is clearly very destructive (Menzies and Cox, 1996) and it is not a collecting technique we have employed. The only exception is Macroplea, whose cocoons can be found amongst the leaves and stems of their host plants (Monahan and Caffrey, 1996). There is no organised recording scheme for the Irish donaciines so the first stage in preparing this review was to construct a database of all the records.