Orobitis cyaneus (Linnaeus, 1758)
Violet Seed Weevil
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
OROBITIDINAE Thomson, C.G., 1859
OROBITIS Germar, 1817
This species is generally common throughout Europe from the Mediterranean north to the UK and reaching the Arctic Circle in Fennoscandia, to the east it occurs through Asia Minor and Russia to Siberia and Central Asia. In the UK it is very local though sometimes common throughout England, Wales and southern Scotland; in Wales and the West Country it is mostly coastal and in England generally it is sporadic with many records from Sussex and the west midlands, it is present on Anglesey and the Isle of Man but there are very few records from the western Isles. Here typical habitats include open and dry areas bordering wetlands, sand dunes, grassland and woodland rides but on the continent it appears to be more eurytopic occurring in damp meadows, peat bogs, fens, pastures, deciduous woodland, hedgerows and domestic gardens, a reflection of the abundance of both the beetle and its various hosts. Adults occur year-round although most probably remain within the cocoon through the winter, they become active from January, depending on the season and mating begins after a period of feeding. Oviposition begins in April or May when females lay eggs in immature ovaries, larvae feed on the seed capsule and developing seeds through the spring and summer and pupation occurs from July to September at or near to the feeding site, resulting adults may overwinter directly at the pupation site or become active and feed beforehand depending on when they emerge. Hosts include a range of Viola species and the adults can be extremely difficult to find, when disturbed they withdraw their appendages and display thanatosis, often for long periods, and strongly resemble a host seed; the long femora are held parallel and oblique to the body, resembling the scar on a seed which marks its point of attachment to the seed pod. We found several specimens in local woodland by grubbing in the soil among a group of host plants. UK specimens are apterous or brachypterous but fully-winged specimens have been recorded on the continent although it is not known whether they can fly as they were from pitfall-trap samples.
Adults are small, 2.2-3.0mm, entirely dark bluish-black above but for pale scales around the scutellum, have extensive and dense pale scales below and dark to pale red appendages. The pronotum and elytra appear smooth and glabrous but are finely punctured and have a fairly dense covering of tightly adpressed elongate-oval dark scales. Head from above visible as large convex eyes separated by a vertex about as wide as the base of the rostrum. Rostrum about as long as the head and pronotum combined (view from the side), broader and with dark and pale scales before the antennal insertions, narrower and more sparsely scaled towards the apex, scrobes oblique and not visible from above. Antennae 11-segmented, scape short and gradually widened towards a truncate apex, funiculus 7-segmented and weakly expanded to a narrow and elongate 3-segmented club. Pronotum widely transverse, broadest at sharply-acute posterior angles and strongly narrowed to a rounded anterior margin, surface smoothly and very strongly convex Scutellum with dense pale creamy scales which contrast with a few elongate white scales on the adjacent areas of the pronotum and elytra. Elytra broadly-oval and continuous in outline with the pronotum; broadest below the shoulders and strongly narrowed to separately and narrowly rounded apices, very convex and only weakly deflexed laterally. Striae narrow and sharply defined between broad and flat interstices. Legs long and robust, femora lacking a ventral tooth, broadened from the base and constricted before the apex, tibiae narrow and near-parallel-sided, slightly expanded externally at the apex and armed with a small mucro in the male. Tarsi pseudotetramerous with the third segment strongly bilobed and the terminal segment elongate and with a terminal process slightly longer than the claws which are connate and toothed at the base.
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OROBITIDINAE Thomson, C.G., 1859
Violet Weevils
This small group includes 4 or 5 species in 2 genera and is often considered sufficiently distinct to form a subfamily of the Curculionidae Latreille, 1802 but other systems will be found in the literature e.g. it is included in the tribe Orobitidini Thomson, C.G., 1859 and the supertribe Orobitiditae Thomson, C.G., 1859 of the Ceutorhynchinae Gistel, 1848 in the Palaearctic catalogue. Parorobitis Korotyaev, Konstantinov & O’Brien, 2000 includes 2 Neotropical species while Orobitis Germar, 1817 includes 2 or 3 Palaearctic species; O. nigrina Reitter, 1885 which is restricted to southeast Europe, the transpalaearctic O. cyanea (Linnaeus, 1758) and there may be a distinct species recorded from Greece, O. signata Panzer, 1795. All species are small, 2.0-3.5mm, with extremely and continuously convex pronotum and elytra, Orobitis species are dark coloured, sometimes with a metallic reflection, while those of Parorobitis are dark with pale spots to the pronotum and transverse pale elytral maculae. Among the European fauna they are quite distinctive due to the overall appearance and might only be mistaken in the field for certain Apioninae, but the convex form and geniculate antennae should be obvious. In both European species hosts include various species of Viola L. hence the common name.