Taxonomy
Platycheirus immarginatus
Distribution
Species Biology
Preferred environment
Wetland; in atlantic parts of Europe particularly in freshwater coastal marshes; fen and flush systems in blanket bog; cut-over raised bog; taiga wetlands. Until recently, this species has been so totally confused with others, especially P. perpallidus and P. ramsarensis, that European distribution data and ecological information supposedly relating to P. immarginatus have to be treated with caution. But, wherever it occurs, P. immarginatus is essentially a wetland species. In Ireland it has been found almost at sea level in the west, in coastal freshwater marsh and in flush fen systems in bogs. In the midlands it occurs in fen and in the east it has been recorded at some altitude (750ft.) in the Wicklow Mountains, with flushes on the periphery of transition mire/fen. In all cases, it is found with tall vegetation. But the records are few and scattered. This species shows every indication of having special requirements which are not easily identified from the character of the localities at which it is found. Brancquart (1999) identifies different types of life history strategy characterising generalists and specialists among syrphid species with aphidophagous larvae and it would seem very likely that P. immarginatus is one of those species adapted to exploiting some specific aphid (or other plant bug). This stratagem would restrict it to localities where its chosen prey occurs, because, although such a syrphid species is able to use a food source not available to other syrphids it becomes itself unable to exploit more generally-available, alternative prey. In Norway, where available information has been recently revised (Nielsen, 1999), the situation of P. immarginatus is similar to that pertaining in Ireland - it occurs from within the arctic circle to the south coast. In the north it occurs in mires in taiga and tundra and in the south at coastal sites. But all together there are confirmed records from only 4 50km UTM grid squares in the entire country.
Adult habitat & habits
Lies among tall waterside vegetation; as easily detected by use of a sweep net as by direct observation.
Flight period
End May/beginning September. Larva: not described.
Flowers visited
Scirpus maritimus.
Irish reference specimens
In the collections of NMI and UM
Determination
Speight and Goeldlin (1990), Vockeroth (1990). The species is illustrated in colour by Torp (1994). This species is almost indistinguishable from P. perpallidus (see under P. perpallidus).
Distribution
World distribution(GBIF)
Uncertain, due to confusion with other species, until recently; in Britain present from the Scottish Highlands to the south coast of England, where it is not infrequent in coastal localities; from various coastal sites in Ireland; its presence cannot yet be confirmed for France or central Europe, but it occurs in Sweden, Denmark, the Netherlands and Belgium. From the information and figures provided by Vockeroth (1990) this species would seem to also occur in N America, from Alaska south to southern California. Recorded as occurring in Ireland in Coe (1953), but at that time this insect was confused with P. clypeatus, P. occultus, P. perpallidus, P. ramsarensis and various other Platycheirus species. It is an extremely infrequent species where it occurs elsewhere along Europe's Atlantic seaboard and is apparently absent from central, southern and eastern parts of the continent. It is a moot point whether the North-American P. immarginatus is indeed that species or some other, closely related taxon.
Irish distribution
The presence of P. immarginatus in Ireland was confirmed by Speight and Goeldlin (1990). In western Ireland recorded from localities scattered from Donegal to Kerry, most of them coastal. There are also a few records from east coast localities and inland records from Kildare and Mayo. The apparent restriction of this species to isolated localities, albeit scattered the length and breadth of the island, gives a relictual distribution pattern to the occurrence of P. immarginatus in Ireland. In nearly all cases it is associated with small-scale landscape features susceptible to drainage, or even partial drainage, of the site. Considering these various strands of data together, P. immarginatus should probably be regarded as vulnerable in Ireland.
Temporal change
Records submitted to Data Centre in 2024
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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.