Cis bilamellatus (Wood, 1884)


Our only non-native Ciid, the history of which is interesting. First recorded as British in January 1884 by T. Wood (1884) from a single male specimen found beneath decaying pine bark at West Wickham (south of London). In September of that year it was found at the same site ‘in utmost profusion’ in boleti on decaying birch, and again that month a single male was taken from ‘a large fleshy fungus upon an ash’ a mile and a half from the site of the pine capture. A little later Fowler (1890) refers to Wood’s records and adds ‘it has not, however, been recorded from any other locality, either British or foreign.’ Fowler’s observation, considering the amount of collecting going on generally (and it must be admitted that Ciids were probably not the most popular group), reflects the fact that bilamellatus was initially slow to expand its range. The next (known) record is from Mitcham, Surrey in 1891 and following this from Shirley common, Surrey in 1904, only half a mile from Wood’s original discovery (Paviour-Smith, 1960a). Records from the following twenty years show an expansion around the London area including Kent (Orpington, Otford and Westerham), Surrey (widespread), Middlesex (Highgate) and, most satisfyingly from our point of view, from Watford, Herts. in 1921 by N.H. Joy (Hence Joy quoted the species’ occurrence in his 1932 handbook as Eng.S; very local). And so for the fifty years following its discovery the expansion of its range was restricted to the London region but it must be acknowledged, as ever, that these records also reflect the activities of coleopterists of the time. The following ten years, to 1934, shows further records within this area and also from Windsor and Arundel but it was only after 1934 that the species started to become widespread with e.g. records from Woking (1935), Oxon (1936), Nottinghamshire (1938), Cheshire (1940’s), Cambridge (1949) and Hampshire (1950). Twenty-six years after Wood’s original discovery G.C. Champion found that Cis bilamellatus Fowler, 1884 (as it was then designated) was synonymous with C. munitus Blackburn, 1888, a species widespread in Australia, and so the obvious route into the U.K. was among imported timber etc. and Paviour-Smith (loc.cit.) makes a convincing case for its introduction among herbarium specimens destined for e.g. Kew Gardens.

With the exception of the northeast the modern distribution extends throughout England and Wales including the Isle of Wight and Anglesey and into southern Scotland north to Fife and Stirling (here we are considering only data given on the latest (June, 2009) NBN map.) The modern distribution will obviously be influenced by the distribution of the various fungal hosts (and more especially of Piptoporus betulinus, considered by Paviour-Smith its preferred host) and also upon ecological factors throughout these distributions. Predators include a Cecidomyiid fly larva and a Bethylid wasp and competition with other Ciid and Dipterous larvae may limit population growth as will the availability of the host over a wide area. Various factors are thought to have contributed to the species (eventual) success although it is known to be sensitive to low temperatures and a bad winter can kill whole populations; lack of close woodland maintenance during the wars may have assisted the species and it has been proposed that success may be due to exploitation of an apparently empty niche i.e. the decomposition of dry dead samples of Piptoporus betulinus, a role fulfilled by Diaperis boleti on the continent where Ciids are rare in this fungus (Paviour-Smith, 1960b). The species is drought tolerant and does not colonise Piptoporus sporophores until the spring following the winter spore production phase and there is evidence that C.bilamellatus and C.bidentatus may share P. betulinus as a habitat by thriving best under different conditions (Paviour-Smith, 1968). C.bilamellatus is common and usually abundant throughout our Watford area; certainly our most common Cis and, along with C.octotemnus, by far our most common Ciid. Adults are abundant year round and between 2007 and 2009 there has been an obvious increase in numbers during the spring. It would be impossible to outline a typical habitat because the species is so very common and likely to occur wherever there is suitable host i.e. the fruiting bodies of various fungi, and the adults have occasionally been extracted from bark samples without obvious fungal associations. All stages occur in fruiting bodies and the following species of fungi are recorded as hosts by Whitehead (1999): Laetiporus sulphurous on cherry (Prunus avium (L.)) (As locally in Whippendel wood), Polyporus squamosus on elm (Ulmus procera) and ash (Fraxinus excelsior), Ganoderma applanatum on beech (Fagus sylvatica) and oak (Quercus robor), Ganoderma resinaceum Baudi (which is quoted as especially favoured) on Turkey Oak (Q.cerris), Coriolus versicolor on sycamore (Acer pseudoplatinus) and Piptoporus betulinus on birch (Betula pendula). In general bilamellatus is likely to occur with other Ciids; locally they are often in company with octotemnus. Populations within a single sporophore tend to be large with early stages occurring year round, for those patient enough to dissect a sample at x10 the male pupae are obvious with head and pronotal plates as the imago. Whitehead quotes over 400 adults of different generations with numerous larvae from a single sporophore of Ganoderma resinaceum from Turkey Oak, and we have observed this density on several occasions during 2007 and 2008 from Coriolus versicolor in Cassiobury Park. The life cycle is passed within the host and populations may persist for several years while the dead fungus is still attached to the tree, dispersal occurs in the spring and, of newly matured adults, in the autumn. Significantly higher proportions of females first colonise newly dead fungi in the spring, after the F1 generation the ratio is 1:1. The following list of fungi in which bilamellatus is known to breed is taken from Paviour-Smith(1960b). Pleurotus sapidus, Polyporus squamosus, Poltporus sulphurous, Polyporus betulinus, Polyporus adustus, Ganoderma applanatum, Irpex sp. and Polystictus hirsutus. It has also been recorded from Polyporus dryadeus and Polystictus versicolor.

Males may be identified by the broad erect plates on the clypeus and anterior margin of the pronotum, these vary greatly in size and this is not proportional to the size of the specimen, sometimes they are only weakly developed but they are always obvious. The clypeal plate is flat and straight while the pronotal plate is concavoconvex and weakly recurved, the apical margin varies from being weakly sinuate to strongly incurved. No other ciid has these plates although males of some species e.g. Cis bidentatus Ol. have the anterior margins of the clypeus and pronotum produced into blunt teeth. Females will soon become familiar by association. 1.5-1.9mm (Joy) although smaller specimens occasionally occur. Overall form elongate, parallel and somewhat cylindrical. Colour varies from pale to dark brown with the appendages usually lighter. Upper surface with quite dense short and pointed, semi-erect golden brown scales, these become obvious when the specimen is rotated under strong light. Antennae 10-segmented; two basal segments large and broad, 3 elongate, 4-7 small and quadrate, 8-10 much larger and forming a loose club. Pale with club darker, inserted in front of eyes. Vertex flat; distinctly punctured and microsculptured and therefore dull in the female, somewhat shiny with puncturation and sculpture weaker in the male. Clypeus produced in male, bordered and with the anterior margin incurved in the female; sometimes this margin is weakly produced forward by the anterior angle. Eyes convex and protruding. Pronotum slightly transverse; generally about 11:13, front angles obtuse and not, or only slightly, visible from above. Surface uneven (varies), microsculpture a little weaker and puncturation better defined in male; punctures separated by a little less than their diameter, in female a little finer and more dense. Anterior margin produced in male. Bordered all round in female; broadest at or slightly in front of rounded hind angles. Prosternum raised into a median longitudinal ridge which becomes stronger to the hind margin of the front coxae. Scutellum triangular, punctured as surrounding elytra. Elytra relatively short, generally about twice as long as pronotum or sometimes a little shorter than this. Surface finely rugose, puncturation fairly dense and shallow but often obscure towards apex. Legs short; femora and tibia about equal in length, front tibiae gradually and only moderately widened to apex and produced into a blunt external tooth apically. Tarsi 444; 1-3 short, 4 broadened to apex and longer than 1-3 combined. Claws relatively large, smooth and curved and weakly appendiculate.

FOWLER, W.W. Vol. IV p.211
PAVIOUR-SMITH, K. 1960a. The invasion of Britain by Cis bilamellatus Fowler (Coleoptera: Ciidae). Proccedings of the Royal Entomological Society of London (A) 35:145-155
PAVIOUR-SMITH, K. 1968 A POPULATION STUDY OF CIS BILAMELLATUS WOOD (COLEOPTERA, CIIDAE). Journal of Animal Ecology 37:205-228 British Ecological Society
WHITEHEAD, P.F. 1999 Observations of Ciidae (Coleoptera) with particular reference to mycophagy. Entomologists Monthly Magazine 135:123-132
WOOD, T. 1884 A new species of Cis. Entomologists Monthly Magazine 21:130-131 and (a further note) 212.