Wednesday 22 May
Weevil (Procas granulicollis)
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Weevil fact file
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This distinctive weevil is dullish black in colour. It has a dappled appearance due to the presence of patches of white hair-like bristles known as setae (2). Like all weevils, it has a prominent elongated snout (rostrum). This weevil was first discovered and described 1848, but was then considered to be a form of the similar weevil Procas armillatus. It was recognised as a distinct species in 1990 (4).
- Length excluding rostrum (snout): 4-7 mm (usually 5 mm) (2)
Very little is currently known about the ecology of this species. The adults are associated with bracken (Pteridium aquilinum), and feed on climbing corydalis (Ceratocapnos claviculata), leaving distinctive ‘half-moon’ feeding damage on the leaves (5). Studies have shown that in captivity, the adults are usually nocturnal, and hide in bracken litter during the day (5). Adults have been found in the wild between March and August and December and January. Highest numbers occur from late April to the end of June. This suggests that this species breeds in summer, and the new generation of adults overwinters after emerging in August. However, more research is needed to determine if this is the case (2).
Larvae belonging to this group of weevils live inside plant roots, however, the larvae of this weevil have not yet been found in the wild, and so the details of its life cycle are a mystery. The roots of climbing corydalis are too thin to accommodate them, and it is thought they may live inside bracken rhizomes, although searches have so far proven unsuccessful (2).Top
This species was, until recently, believed to be endemic to Britain (found no-where else in the world). It has, however been found in northern Spain, and it is thought that it may also occur in other countries of western Europe (2). Procas granulicollis has a scattered UK range that extends from southern England to south-western Scotland (2). It has been found in eighteen localities, and it is expected that it is more widespread than previously thought (2).Top
This weevil is typically found in clearings in broadleaved woodlands, where bracken (Pteridium aquilinum) grows. It has also been recorded under birch (Betula) and alder (Alnus) on a riverbank and in conifer plantations (2). In all cases, a supply of the foodplant climbing corydalis (Ceratocapnos claviculata) is required (2).Top
Classified as Indeterminate in Great Britain (3).Top
The threats currently facing this species are not known for certain (2), although clear-felling and land-use changes may be problems (6). Climbing corydalis is very prone to grazing damage, and scrub growth in clearings could create too much shade for the species (2).Top
Procas granulicollis was selected as a priority species under the UK Biodiversity Action Plan (UK BAP), mainly as a result of its believed endemic status. Even though the species has now been found in Europe, the UK still holds internationally important populations, and therefore has an obligation to conserve it (2). The conservation of this weevil is co-ordinated by the Countryside Council for Wales. The Species Action Plan aims to maintain all known populations; most sites are designated Sites of Special Scientific Interest (SSSIs), or National Nature Reserves (NNRs), and therefore receive a degree of protection (3). Research is needed into the life-cycle of this weevil and into optimum management techniques of the adult food-plant, climbing corydalis (2).Top
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Information authenticated by Adrian Fowles of the Countryside Council for Wales:
- A species or taxonomic group that is only found in one particular country or geographic area.
- Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Rhizomes are thickened, branching, creeping storage stems. Although most rhizomes grow laterally just along or slightly below the soil's surface, some grow several inches deep. Roots grow from the underside of the rhizome, and during the growing season new growth sprouts from buds along the top. A familiar rhizome is the ginger used in cooking.
- National Biodiversity Network Species Dictionary (September 2002): http://www.nhm.ac.uk/nbn/
- Fowles, A. (2003) Weevils of Wales Procas granulicollis: http://thasos.users.btopenworld.com/procas.htm
- UK BAP (September 2002): http://www.ukbap.org.uk
- Kenward, H. K. (1990) A belated record of Procas granulicollis Walton (Col., Curculionidae) from Galway, with a discussion of the British Procas spp. Entomologist's Monthly magazine, 126: 21-25.
- Fowles, A. P. (1992) Observations on Procas granulicollis Walton (Curculionidae). The Coleopterist1: 19-20.
- Hymen, P. S. and Parsons, M.S. (1992) A review of the scarce and threatened Coleoptera of Great Britain: Part 1. JNCC, Peterborough.
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