DONACIINAE Kirby, 1837
All species occur in waterside habitats, with some being gregarious and active in hot weather.
This small subfamily includes about 200 species in 7 genera although the generic limits are not certain e.g. Donacia Fabricius, 1775, the largest genus in the group, includes several subgenera of which at least one, Donaciella Reitter, 1920, is often considered to be a distinct genus. It seems that no satisfactory tribal system has been worked out for the group but 3 tribes are variously recognized; Donaciini Kirby for Donacia, Sominella and Donaciaster, Haemoniini Chen for Macroplea and Neohaemonia, and Plateumarini for Plateumaris and Poecilocera. The group has a Holarctic distribution with several species of Donacia extending into Southeast Asia, and a single species of Donacia occurring in New Guinea and Australia. The single genus Donaciaster Fairmaire, 1901 extends into Africa. Several fossil species are known from Japan e.g. Donacia uedana Hayashi, 2000, Donaciella nayaokana Hayashi, 1997, Plateumaris virens Hayashi, 1999 and P. dorsata Hayashi, 1997 from the Pleistocene, and Plateumaris kinugasama Hayashi, 2001 from the Miocene. The largest genus of the group is Donacia with about 100 species in 3 subgenera, it is most diverse in Asia, and about 30 species in 2 subgenera occur in the Nearctic zone. The only member of the subgenus Cyphogaster Goecke, 1934, D. C. australasiae Blackburn, 1892, occurs in southern New Guinea and around the northern and eastern coasts of Australia. Donaciella Reitter, 1920 includes 4 or 5 Palaearctic species often included as a subgenus of Donacia; they are distinct in having the dorsal surface finely and densely pubescent. One species, D. cinerea Herbst, 1784, occurs in the U.K. Plateumaris Thomson, C.G., 1859 is a Holarctic genus with most species occurring at higher latitudes, and it is proportionally better represented in the Nearctic than Donacia, with 17 out of a total of 26 species occurring in the United States and Canada. Poecilocera Schaeffer, 1919 includes the single species, P. harrissi (LeConte, 1851) from eastern North America. Donaciasta Fairmaire, 1901 includes 6 species and extends the global distribution of the subfamily; a single widespread species, D. assama (Goecke, 1936), is distributed from northeast India and through southern China to North Vietnam while the others are African; D. dentata (Pic, 1936) from Mozambique, D. goeckei Monrós, 1958 from the Congo, D. luridiventris (Lacordaire, 1845) from Cameroon and Liberia, and there are 2 Madagascan endemics: D. perrieri (Fairmaire, 1901) and D. abortiva (Fairmaire, 1899). Sominella Jacobson,
1908 includes 2 Palaearctic species. The remaining 2 genera are morphologically distinct from the rest of the subfamily (see below) and are sometimes included in a separate tribe, the Haemoniini Chen, 1941. Macroplea Samouelle, 1819 includes 4 Palaearctic species while Neohaemonia Székessy, 1941 includes 4 Nearctic species.
Medium-sized beetles, 5-15mm The species are very distinctive among the Chrysomelids and fall into 2 distinct morphological groups, both of which are instantly recognizable as members of the subfamily; Macroplea and Neohaemonia lack the metallic dorsal surface and the expanded tarsal segments, and have the outer apical elytral angle produced into a distinct tooth. All species have a characteristic broadly elongate shape with the head prognathous and having distinct temples. The dorsal surface is usually strongly microsculptured and metallic; most are bronze, green or coppery and many have longitudinal stripes of contrasting colour on the elytra although in some species of Plateumaris e.g. P. rustica (Kunze, 1818) the body is entirely metallic black. The majority are glabrous but a few species of Donacia, sometimes considered to constitute a separate genus, Donaciella Reitter, 1920, have fine and dense dorsal pubescence. The eyes are round, convex and entire, a character that will distinguish them from the Criocerinae Latreille, 1807 and the Sagrinae Leach, 1815 where they are emarginate on the anterior margin. The vertex is convex, sometimes only weakly so, and often bears a longitudinal impression, otherwise the head lacks well-defined sutures e.g. the X- or H-shaped anterior impression seen in many other chrysos. The antennae are 11-segmented with all but the second segment very elongate. The head is as wide as, or a little narrower than, the pronotum, and both are distinctly narrower than the elytra. The pronotum is quadrate to elongate and usually rather parallel-sided being at most broadened towards the anterior margin, and is often constricted about the middle. The anterior and posterior margins are strongly bordered, all the angles are distinct and the lateral margins lack distinct borders. The surface often has a longitudinal impression and the cuticle either side is variously convex; often widely domed. The anterior prosternal margin is wide and the pro-coxae are round, convex and closely approximated, the prosternal process being reduced to a narrow ridge; the meso-coxae are round, prominent and widely separated, the mesosternum has a deep central longitudinal impression and the meta-coxae are quadrate and widely separated, reaching to the elytral epipleura. The elytra are subparallel to about half way and then narrow to a rounded or truncate apex, in some species e.g. Donacia crassipes Fabricius, 1775 there is a distinct albeit small tooth on the sutural angle. The shoulders are well-developed and each elytron has 10 distinct and usually strongly punctured striae, the cuticle often being transversely wrinkled, sometimes strongly so. In some species there are distinct impressions, often from below the shoulder obliquely to the suture and sometimes transversely so across the middle. The legs are long and robust; in many the femora are very long and dilated, sometimes only towards the apex, and in some they bear one or more teeth on the ventral margin- a character that is often sexually dimorphic-the tibiae generally have a single spur on the inner apical angle although this is missing from the hind tibiae of some Donacia. Tarsal formula 5-5-5; the two basal segments are broad, the third broad and deeply lobed, the fourth is small and the fifth is long and curved. In Neohaemonia and Macroplea the segments are long and cylindrical, the last segment especially so. The claws are curved and lack a distinct basal tooth. All species are fully winged and fly readily. Twenty one species included in three genera occur in the U.K. and these characteristic of the group as a whole.
All stages are associated with marginal and aquatic vegetation and the adults are easily observed active on leaves or flying among foliage in hot weather although those of Neohaemonia and Macroplea are rarely seen as they spend most of their time submerged on roots and rhizomes; the Nearctic Neohaemonia is associated with Potamageton (a genus of more than 100 species of herbaceous pondweeds) while the Palaearctic Macroplea is more widely polyphagous. Three species of Macroplea occur in Europe of which one, M. pubipennis (Reitter, 1875), extends from the Baltic to northern Scandinavia but is absent from the U.K. The widespread eastern Asian and Japanese species M. japana (Jacoby, 1885) has been trialled, and been found unsuitable, as a biocontrol agent for Hydrilla verticillata (L.), the only member of the Hydrocharitaceae, an invasive aquatic weed that is widespread in cool and warmer waters of Asia, Europe, Africa and Australia. M. mutica Fabricius, 1792 is a widespread European species extending east to the Caspian sea and north into Scandinavia and the U.K. although it is very local and considered to be endangered through much of its range, here it has a patchy distribution in the east of England; hosts include Potamogeton pectinatus, Zostera marina, Zannichellia palustris and Ruppia maritima. Macroplea appendiculata (Panzer, 1794) occurs throughout central and northern Europe extending into the U.K. and occurring locally north to southern Scotland, hosts include species of Potamogeton, Myriophyllum, Sparganium, Sagittaria, Carex (sedges), Typha and others. All species of Macroplea have a long season, from early spring until October or November. The Holarctic genus Plateumaris Thomsom, C.G., 1859 has been recorded on a wide range of hosts; mostly species of Cyperaceae as well as some Juncaceae, Araceae, Ranunculaceae, Iridaceae and Graminaceae. Four species occur in the U.K. and are associated with a rather narrow range of hosts; P. sericea (Linnaeus, 1758) on Iris pseudacorus and some Carex species, P. bracata (Scopoli, 1772) on Phragmites communis, P. rustica (Kunze, 1818) on Cladium mariscus and some Carex species, and P. discolor (Panzer, 1795) on Carex. The large genus Donacia is similarly widely polyphagous, occurring on many species of Typha, Sparganium, Phragmites, Carex and Scirpus etc. Fifteen species occur in the U.K. and of these several are primarily associated with certain hosts e.g. D. crassipes Fabricius, 1775 with Nymphaea and Nuphar (water-lilies), D. versicolorea (Brahm, 1791) with Potamogeton nutans, D. semicuprea Panzer, 1796 with Glycera (sweet-grass), D. obscura Gyllenhal, 1813 with Carex rostrate, and D. dentata Hoppe, 1795 with Alisma (water-plantains). On the other hand two species, D. vulgaris Zschach, 1788 and D. simplex Fabricius, 1775, occur on a very wide range of hosts. The single Australian species, D. australasiae Blackburn, 1892, occurs on a range of water-lilies; Nymphaea L., Nymphoides Séguier, and Ondinea den Hartog.
Donacia versicolorea (Brahm, 1791) larvae
Adults are mostly conspicuously coloured, often bicoloured, and strongly metallic, and in order to appreciate this they need to be seen under sunlight in the wild. They tend to occur in large colonies and are very active in warm weather; they walk quickly around the host stems and fly readily when disturbed. They will soon occur by sweeping riparian vegetation and often several species will occur together, in the UK there is nothing to confuse them with and so the common species will soon become familiar, some e.g. D. semicuprea, will be recognized by association with the host plant. Most species become active in early or mid-spring and continue into the summer, sometimes into October or November. The presence of adults will soon be recognized from their feeding signs; mostly they scrape off the surface layers of cells from leaves and leave longitudinal patches of translucent tissue. Eggs are laid on leaves or stems near or under the water surface, generally in rows parallel to the leaf or stem axis, and usually covered in with a clear gelatinous mass. The larvae are pale creamy in colour and have well-developed legs, they emerge within a week or two and mostly feed on submerged roots and rhizomes from which they also obtain oxygen by inserting specialized hook-like processes on the abdominal apex into the aerenchyma tissue, they also obtain air by direct diffusion from the water. Both larvae and adults carry symbiotic organisms that allow them to digest cellulose. Pupation occurs in an air-filled cocoon attached to submerged roots and stems. Most species overwinter in the larval or pupal stage but some adults will eclose in the autumn and remain in the cocoon until the spring.
Donaciinae are distinguished from other Chrysomelids by the following combination of characters:
Elongate species with the head prognathous; the mandibles are sometimes produced forward but the head is never rostrate. Eyes protruding and entire, neck constricted behind distinct temples. Pronotum cylindrical or nearly so, sometimes constricted about the middle but lacking lateral borders. Basal antennomere elongate.
Our three U.K. genera are very distinct:
Elytra not metallic, truncate with the outer apical angle produced into a strong tooth. Tarsal segments cylindrical, the last tarsomere longer than the others combined.
Elytra metallic, usually brightly coloured. Elytra not produced at the outer apical angle. Third tarsomere strongly bilobed, the last not as long as the others combined.
More convex species. Elytral apex rounded, the suture inverted before the apex. Tibiae more robust. Mandibles protruding. First abdominal sternite as long as the others combined.
Less convex species. Elytral apex obliquely truncate, the suture not inverted before the apex. Tibiae less robust. Mandibles short, not protruding. First abdominal segment longer than the others combined.