Pyrophaena granditarsis (Forster, 1771):99

Pyrophaena species are similar to Platycheirus (some authors consider Pyrophaena as a subgenus of Platycheirus) but differ by having the wing shorter than abdomen; abdomen broad, or mostly red, or black with 2 pale maculae on tergum 3.

Adapted from Vockeroth (1992).

MALE.

Head: Face nearly vertical, with prominent tubercle, very slightly silver pollinose except on tubercle. Antenna black. Thorax shining to subshining, with white to yellow pile. Wing membrane entirely trichose. Halter capitulum yellow. Legs black with basal one-third to one-fifth of pro- and mesotibiae and basal one-fifth of metatibia yellow. Protrochanter with some short fine pile below; profemur with very short stiff black setae in irregular anteroventral and irregular posteroventral row on basal three-fifths; protibia rather stout on apical three-fifths but not at all depressed; first tarsomere with large triangular anterior process having apical half strongly depressed; last four tarsomeres short and wide but only slightly depressed. Mesofemur posteroventrally with group of short stiff black setae near base; mesotibia similar to protibia; first four tarsomeres strongly depressed, each with broad apically rounded anterior process progressively shorter on first to third tarsomeres. First tarsomere of metaleg rather strongly swollen, about four times as long as greatest depth.

Abdomen rather broad, black with extensive yellow-orange areas as follows: tergum 2 yellow-orange except anterior one-third and narrow lateral margins; anterior black area with triangular posteromedian extension extending as black median line to posterior margin in some specimens; tergum 3 yellow-orange except posterolateral angles; basal fascia on about one-third of tergum 4 yellow-orange; fascia commonly emarginate posteriorly or divided into pair of maculae. Sterna black with posterolateral angles of 2, all of 3, and base of 4 yellow-orange. Genitalia: Surstylus with poorly developed basal process. Paramere subtriangular, with spine scarcely differentiated.

FEMALE.

Frons shining except for two tiny silvery pruinose lateral spots at two-thirds its length; face broadly shining medially. Legs mostly yellow with following areas black or rarely brown: coxae, trochanters,
protarsus, last four tarsomeres of mesotarsus, small to large mark just beyond mid length of anterior surface of metafemur, broad ring on about apical two- to four-fifths of metatibia, and metatarsus; femora without stiff setae. Protarsus moderately depressed; first tarsomere slightly widened towards apex; next three tarsomeres each wider than long; fifth tarsomere subquadrate. Mesotibia and meso- and metatarsi rather slender. Abdomen with yellow-orange markings similar to those of male. Tergum 2 usually with narrow and obscure to broad and distinct posterior black band strongly produced forward
laterally in some specimens; tergum 3 with similar posterior black fascia; tergum 5 with large triangular anterolateral yellow-orange macula. Sterna yellow-orange.

Variation.

Some specimens from Utah and all those in a long series from the Mojave Desert, California, have the abdomen more extensively yellow-orange than do other Nearctic specimens. Some males from Utah are intermediate in color pattern, with tergum 5 with small to rather large sublateral pale spots. The male terminalia of all are as in the darker northern form. Vockeroth (1992) considered these pale southwestern specimens (var. apicauda Curran) to be color variants of P. granditarsis.

Pyrophaena granditarsis (Forster, 1771).

Forster, J.R. (1771) Novae species insectorum. Centuria I. viii + l00 pp. Davies & White, London. [1771.12.01]

Pyrophaena was described by Schiner (1860) for Syrphus rosarum Fabricius, 1787. Vockeroth (1990) considered it a synonym of Platycheirus, and some authors (Thompson 2010) gave to Pyrophaena the status of a subgenus.

Mengual et al. (2008) using molecular characters recovered Pyrophaena granditarsis as a different genus from Platycheirus and considered Pyrophaena a valid genus.

Synonyms:

Pyrophaena digitalis Fluke, 1939: 367.

Musca granditarsa Forster, 1771: 99.

Syrphus ocymi Fabricius, 1794: 309.

Musca confusus Harris, 1780: 110.

Syrphus lobatus Meigen, 1822: 336.

Pyrophaena granditarsa var. lindrothi Ringdahl, 1930: 173.

Pyrophaena granditarsis var. apicauda Curran, 1925: 115.

Musca ocymi Turton, 1801: 651.

GenBank accession number for this species are: protein-coding COI gene (EF127321), rRNA 28S gene (EF127400) and 18S gene (EU431551).

Body lenght: 7.7-10.5 mm (Vockeroth 1992).

Genus Pyrophaena, like Syrphocheilosia, Pseudoplatychirus, Spazigaster and Rohdendorfia, were treated as subgenera of Platycheirus by some authors (Hull 1949a; Vockeroth and Thompson 1987; Thompson and Vockeroth 1989; Thompson and Rotheray 1998) and others treated it as a separate genus (Williston 1887; Shannon 1921, 1922, 1923; Goffe 1952; Wirth et al. 1965; Dusek and Laska 1967; Shatalkin 1975; Rotheray and Gilbert 1989, 1999). Molecular evidence by Mengual et al. (2008) placed Pyrophaena close to the other traditional subgenera of Platycheirus except Pseudoplatychirus, a hypothesis supported also by larval characters (Rotheray and Gilbert 1999). Shatalkin (1975) also mentioned some differences in the lobes of the surstyli comparing Pyrophaena with Platycheirus.

Adults visit flowers of white umbellifers; Alisma plantago-aquatica, Bidens cernua, Leontodon, Lycopus europaeus, Polygonum cuspidatum, Ranunculus, Senecio jacobaea (Speight 2010).

Flight period (European specimens) for this species is from end of May to September and occasional specimens in October (Speight 2010).

P. granditarsis can be foun from Iceland and Fennoscandia south to northern France and the Alps; from Ireland eastwards through northern and central (very localised in the Alps) Europe into European parts of Russia; across Siberia to the Pacific coast (Kuril Isles). In North America, from Alaska to Quebec and south to Oregon, Colorado and Pennsylvania (Speight 2010; Thompson 2010).

Preferred environment: open ground/wetland; humid, unimproved grassland subject to flooding or not, including oligotrophic Molinia grassland, marsh, fen, edges of raised bogs. Adults flies among tall (1 m or more) ground vegetation; settles on stems of Juncus, Phragmites etc.; males hover at up to 2 m in more open spots within humid grassland etc. (Speight 2010).

Larva of P. granditarsis is undescribed, but this species has been collected in numbers from emergence traps installed over the taller patches of grass that develop around cow pats, in a cattle-grazed, humid grassland and from emergence traps installed over setaside vegetation. Barkemeyer's (1994) reference to occurrence of larvae of this species in cereal crops seems to be in error, since the source he quotes (Chambers et al, 1986) makes no mention whatever of Pyrophaena granditarsis (Speight 2010). It is assumed (e.g. Lundbeck 1916; Coe 1953) that the larva is aphidophagous, but this
is not yet definitely established.

Egg (from Chandler 1968).

White; mean length 817 µ (n = 23, range 705-906 µ), mean width 320 µ; egg markedly pointed at one end; surface patterning of very slightly upstanding oval plates, smoothly margined and tightly packed, pellucid, absolutely unfrosted. Chorionic sculpturing: dots and rods both dorsally and ventrally with only very slight tendency to aggregation into groups. Ecological notes: Eggs never found in the field, but gravid females frequent from June to October notably in wet, grassy habitats; eggs laid singly in the laboratory.