ORSODACNIDAE Thomson, C.G., 1859

No Common Name

Of the two UK species O. cerasi is widespread, while O. humeralis is very local and rare. Both may be found on flowers or by beating a variety of broadleaf trees and shrubs. 

POLYPHAGA Emery, 1886

CHRYSOMELOIDEA Latreille, 1802

Orsodacne Latreille, 1802

O. cerasi (Linnaeus, 1758)

O. humeralis Latreille, 1804

4.4-8mm

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Introduction

This small family of leaf beetles was formerly included as a subfamily of the Chrysomelidae. It contains two subfamilies. The Aulacoselidinae, previously also a subfamily of the Chrysomelidae, contains around 20spp. in two genera; Aulacoscelis Duponchel & Chevrolet, 1842 and Janbechynea Monros, 1953. They are mostly Neotropical in distribution. The Orsodacninae contains a single Holarctic genus, Orsodacne Latrielle, 1802 with four species. There have been many name changes and various species have in the past been included, Fowler quotes 14 while Cox (1981) quotes 10. Orsodacne atra (Ahrens, 1810) is a widely distributed Nearctic species which feeds on the pollen of various rosaceae. The three remaining species are Palaearctic. O. variabilis Baly, 1877 from eastern Europe, Turkey and further south and east to Iran and Kurdistan. O. cerasi (Linnaeus, 1758) and O. humeralis Latrielle, 1804 are both more widespread species.

Description

Orsodacne species are quite distinct, if not a little nondescript, and will quickly be recognized as chrysomelid, with the filiform antennae and bilobed third tarsal segment, and suggestive of criocerinae. The following features will identify the genus but within the British fauna they are distinct on gross morphology. 4-8mm. Head with a narrow neck so that the eyes are some distance from the pronotal front margin. The eyes are large and prominent, round and not notched. Antennae 11-segmented and filiform; basal segment dilated, 2 quadrate and 3-11 elongate. Segments 7-11 about 1.5x longer than wide. Inserted before the eyes and behind the mandibles;  insertions separated by a little more than the length of the first segment. Clypeus elongate anterior to the antennal insertions. Pronotum smooth laterally; without margins or teeth, constricted sub-basally and much narrower than the base of the elytra. Elytra entire and elongate. Elytral puncturation random but there may be a tendency for these to run into longitudinal series near the suture. Procoxae (visible in lateral view) transverse. Third tarsal segment bilobed. The colour is very variable in all species and so this is not useful for identification, they vary from yellow to metallic  blue  or black.  In the past  several  colour  variations  were  given 

names, this habit is largely ignored nowadays but some notes about these are given under the species descriptions for interest.  Dorsal pubescence variable. Without experience a casual glance in the field might suggest a cantharid but the more convex and broader form of Orsodacne will soon become obvious. Our two British species are readily separated:

UK Species

Orsodacne cerasi

Elytra almost glabrous, with microsculptured surface and diffuse puncturation. Elytra distinctly less shiny than pronotum.

Orsodacne humeralis

Elytra with dense, fine pubescence, shiny and more densely punctured. Elytra and pronotum equally shiny.

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