Cheilosia semifasciata

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Cheilosia semifasciata (Becker, 1894)

Identification ease/difficulty: 5

Status

• Rare in Falk (1991)

Habitat indicator status

• H1 in Stubbs (1982)

Sources of information

• Page 173 in Stubbs & Falk (1983)
• Larval plate Pl. 2e, 2f in Rotheray (1993)
• Map here and page 38 in Ball & Morris (2000)
• Page 259, Pl. F, Fig. 1 in Stubbs & Falk (2002)

Pictures:

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Species account from Provisional atlas of British hoverflies, Ball & Morris, 2000.

Cheilosia semifasciata Becker, 1894 Cheilosia fasciata Schiner and Egger in Coe (1953)

Biology: The larvae form ‘blotch mines’ on the leaves of Sedum telephium in southern England and Umbilicus rupestris in the south-west and Wales. Adults are rarely found far from stands of the larval foodplant. The early flight period may lead to the adults being overlooked, and its presence is probably better established by searching for larval mines (illustrated in Rotheray, 1994). Even these may be difficult to find, as larger larvae completely consume the contents of a leaf causing it to drop, and then move to another.

Distribution: This is a rare species with few recent records. In southern England, where its foodplant is scarce, it is confined to a few scattered localities. In North Wales its food plant is widespread, but recent observations suggest that many patches, even those close to known colonies, are unused. At one strong colony it was noted that the plants remained green and fleshy in late June, whilst at many other localities in the same area they had turned brown and withered. It is possible that the larvae require a plant to be growing in a situation where its leaves remain suitable for larval feeding longer than usual (Adrian Fowles, pers. comm.)

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Datasheet from the Review of Scarce and Threatened Diptera, Falk (1991).

CHEILOSIA SEMIFASCIATA Becker RARE

DISTRIBUTION Old records widely scattered in southern England and extending into North Wales where it still persists.

HABITAT In the English part of its range it is associated with orpine Sedum telephium in broadleaved woods, especially coppice with a rich ground layer of herbs. In Wales it is associated with navelwort Umbilicus rupestris which is widespread and thrives upon stone walls, embankments and rock crevices in acid conditions. However even here it seems to require plants in cooler, shaded areas.

ECOLOGY Larvae phytophagous mining the succulent leaves of both orpine in England and navelwort in more westerly regions such as North Wales. Adults recorded in April and early May and males are said to sunbathe on the ground close to woodland margins. The larval biology is described in detail by Rotheray, G.E. (in press).

STATUS A highly declined species possibly extinct at most of its old English localities though it was discovered at Pamber Forest, Hampshire in 1989. The only known post 1960 records are from North Wales, where it seems to be not infrequent and it may prove to be under recorded in Wales generally because of the early flight period. This species is not listed in Shirt (1987).

THREAT Loss of orpine from English woods through the cessation of coppicing which this plant is largely dependant upon . Navelwort is not so much a woodland plant though the hoverfly is mainly dependent on the plant in this habitat so all forms of woodland loss, intensive forestry and other activities which may reduce the plant should be avoided.

MANAGEMENT Maintain or introduce coppicing at known orpine sites (as much for the conservation of the plant as the fly) in the hope that the fly has survived in a few such sites. In navelwort areas maintain woodland and woodland margins in a semi-shaded state to ensure survival of this plant in shaded situations.