Includes two British species of the genus Orsodacne Lat.; O.cerasi (L.) and O.humeralis Lat.
which has often been referred to (eg in Joy) as lineola Panz. Orsodacne has long been included
within the Chrysomelidae (although the status of Orsodacnidae has also been recognised in the past eg Jolivet, 1948)
and the overall elongate shape and the form of the prothorax is strongly suggestive of the chrysomelid subfamily
Criocerinae. The filiform antennae and bilobed third tarsal segment are typically chrysomelid features and within
this superfamily (and within our fauna as a whole) the following combination of morphomological features will
identify the orsodacnids:
4-8mm. Head with a narrow neck so that the eyes are some distance from the anterior pronotal margin. Pronotum without lateral margins or teeth, constricted before base and narrower than elytra at shoulders. Elytra elongate and randomly punctured, rounded at apex.
In some specimens there is a tendency for the elytral punctures to run in longitudinal series near the middle but overall the random nature will be obvious. Further interesting (and isolating) characters are as follows:antennae filiform with basal segment bulbous, 2 quadrate and 3-11 elongate; 7-10 about 1.5X longer than wide. Inserted behind the mandibles and in front of the level of the anterior margin of the eyes, insertions widely separated, a little wider than the length of the basal segment. Head elongate anterior to the antennal insertions. Eyes entire (not notched). Procoxae transverse (visible from the side). Third tarsal segment bilobed, middle and hind deeply so. Colour varies from dark blue to yellow or a combination of these and a casual glance in the field suggests a robust Cantharid, they also occur at the same time as many cantharids, but with a little experience the broader and more convex form of Orsodacne will be obvious.
Our two species are easily separated (size overlaps):
1. Upper surface glabrous or nearly so, less densely punctured. Elytra dull when compared with pronotum.....cerasi (L.)
-- Upper surface with dense and rather long pubescence, more closely punctured. Eltra shiny.....humeralis Lat.
O.cerasi is featured. The following short description of humeralis (taken mostly from Fowler's O.lineola Panz) is included until we can obtain an empirical description.
4-7mm. Very variable in size and colour, distinct from cerasi by rather long pubescence and thicker puncturation. The thorax is larger, the ventral surface more sparingly punctured and pubescent. The head and 'breast' are usually, but not always, black. The elytra (in both species) are sometimes narrow and convex and sometimes broad and rather flat. Var. humeralis latr. is deep violaceous-blue, almost black, with two red spots towards the base of the thorax and the shoulders of the elytra reddish; the upper surface is sometimes immaculate.
O.humeralis is a scarce (Notable B) species of southeast England west to Hampshire and north to Cambridgeshire and there is a separate group of records north of the Severn estuary; Hereford and Gloucester. But for a single (pre 1950) remote record from Renfrewshire the species is not recorded from Wales or Scotland (NBN June 2009). The host plant is not known. Adults occur on a wide range of flowers between March and June and have been beaten from birch (Betula) saplings and freshly cut cypress branches (Cox) Typical habitat is broadleaved woodland, parkland and land adjoining such areas. A key to first instar larvae of Orsodacne species is given by Cox (1981)
Cox, M.L. 1981 Notes on the biology of Orsodacne with a subfamily key to the larvae of the British Chrysomelidae. Entomologists Gazette 32:123-135
Jolivet, P. 1948 Les Orsodacnidae de la faune francaise. Miscrea ent. 95:33-46.