Taxonomy

Didea alneti

Distribution

Species Biology

Preferred environment

Forest; conifer forest (including western taiga) and plantation; acidophilous Quercus.

Adult habitat & habits

Primarily arboreal, but descends to visit flowers at the edges of clearings, along tracks, beside streams etc. Males hover at 3-4m beside trees, or between their branches. In other syrphids, hovering is normally carried out with the long axis of the body more or less parallel to the ground surface, but D. alneti can hover at a strongly inclined angle, with its head high.

Flight period

Mid May/early September. Larva: Dusek and Laska (1967) figure features of the arboreal larva. Larvae of this species have been found on Larix, Prunus, Salix and Quercus.

Flowers visited

White umbellifers, yellow composites; Cirsium, Plantago, Potentilla, Rosa, Rubus idaeus, Salix, Sambucus ebulus, Valeriana officinalis, Viburnum opulus.

Irish reference specimens

In the collections of SI

Determination

Stubbs and Falk (1983). See Key provided in StN Keys volume. The male terminalia are figured by Dusek and Laska (1967). The adult insect is illustrated in colour by Stubbs and Falk (1983), Torp (1984, 1994) and van der Goot (1986).

Distribution

World distribution(GBIF)

Northern Fennoscandia south to northern France; from Ireland eastwards through central Europe and across Russia to the Pacific coast, Japan and Korea; Mongolia; in N America from Alaska south to Colorado. 

Irish distribution

 Recorded as occurring in Ireland in Coe (1953). The sole Irish specimen known of this species, collected by Stelfox, carries no habitat information on its data labels. The general characterof the locality from which that specimen is derived (Clara, Co.Wicklow), together with what is known of the ecology of the species elsewhere, suggests it is likely to have come from riverside conifer plantation. There is no obvious reason why it would have disappeared from there, or why it would not occur elsewhere in similar situations in Ireland (see also under Melangyna compositarum). However, the species seems to have been declining in western Europe in general during the present century (in Britain it is nearly extinct now). On the continent, this species occurs in association with conifers, especially Abies, but it does not seem to have been able to colonise Irish conifer plantations. As the only Irish record dates from more than 50 years ago and D. alneti has to be regarded as probably extinct in Ireland. In case it persists here, it should be included on any listing of insect species requiring protection in Ireland.

Temporal change

Records submitted to Data Centre in 2021

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References

Publications

Speight, M. C. D. (2008) Database of Irish Syrphidae (Diptera). Irish Wildlife Manuals, No. 36. National Parks and Wildlife Service. Department of Environment, Heritage and Local Government, Dublin, Ireland.

Speight, M.C.D. (2014) Species accounts of European Syrphidae (Diptera), 2014. Syrph the Net, the database of European Syrphidae, vol. 78, 321 pp., Syrph the Net publications, Dublin.

Images