Didea alneti

[stuart]

Didea alneti (Fallén, 1817)

Identification ease/difficulty: 5

Status

• Endangered in Falk (1991)
• Endangered in Shirt (1987)

Sources of information

• Page 134, Pl. 3, fig 17 in Stubbs & Falk (1983)
• Map here and page 54 in Ball & Morris (2000)
• Page 197, Pl. 3, fig. 17 in Stubbs & Falk (2002)

[stuart]

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

Didea alneti (Fallén, 1817)

Biology: The larvae are aphidophagous and usually associated with conifers, although they have also been found feeding on other arboreal aphids such as those on Salix and Lachnus sp. on Quercus. Adults occur in or near woodland, including conifer plantations where they are primarily arboreal, but will descend to visit flowers

Distribution: This species has an unusual distribution, with a several widely separated areas producing a number of records over a period of a few years (e.g. Forest of Dean in the 1890s, Sutton Park around the turn of the century, Speyside area in 1930s) followed by apparent local extinction. This pattern suggests an occasional migrant or vagrant (or accidental import?) that sometimes establishes temporary populations. The only recent records come from Slaley Forest, a large conifer plantation in southern Northumberland, where it was found twice in 1989

[stuart]

Datasheet from the Insect Red Data Book, Shirt (1989).

Didea alneti (Fallen, 1817) ENDANGERED

Identification: Stubbs & Falk (1983), pp. 61 and 134, pl. 3:17.

Distribution: The West Midlands, also Essex, Kent and north Scotland.

Habitat and ecology: Unknown. The larvae will be of the aphid-feeding type.

Status: Always a great rarity, last taken in 1948 in Kent. This is one of four British hoverflies which have not been confirmed as occurring in Britain in the post-1970 period.

Author: A. E. Stubbs.

[stuart]

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

DIDEA ALNETI (Fallen) ENDANGERED

DISTRIBUTION Old records for about 18 sites scattered widely in England and Scotland as far north as Easter Ross with a recent record for Trawsfynydd, Merionethshire (1979).

HABITAT Woodland, favouring rides and woodland edges. Abroad it is said to be associated with conifer plantations though some British records apply to broadleaved woods.

ECOLOGY Larvae probably aphidophagous but details unknown. Adults recorded from May to September which suggests two broods are present and abroad they have been recorded feeding on a wide range of flowers.

STATUS Only a single record since 1948 and seriously declined, as it is a large species unlikely to be overlooked. The nature of the records suggests it may possibly be migratory, with irregular influxes from the continent, though until this can be more fully demonstrated it must be regarded as an extremely rare native.

THREAT Woodland clearance for agriculture and afforestation. The shading out of rides and clearings within woodland.

MANAGEMENT Ensure a good age structure and variety of trees within a wood and maintain open rides and clearings with plenty of flowers for adult feeding.