Platycheirus beringiensis Barkalov & Mutin, sp. n.

Platycheirus beringiensis Barkalov & Mutin, sp. n.

(figs 3B, 5A–F)

Type material. HOLOTYPE, ♂, labeled: Russia: Chukotka, lower reaches of river Anadyr, 64,83° N, 175,96° E, 5 m above sea level, 18.0 7.2013, leg. A. Barkalov, coll. SZM. Paratypes: Russia: 1♂ 7♀, same place as holotype, 18– 29.07.2013, leg. A. Barkalov, coll. SZM; 1♀, same place as holotype, 30.0 7.2013, leg. V. Zinchenko, coll. SZM; 4♂ 17♀, same place as holotype, 18– 30.07.2013, leg. V. Mutin, coll. Valerij Mutin.

Diagnosis. This species is similar to P. immarginatus Zetterstedt, but differs by its larger size, darker colour of abdomen and by the hairs on the male legs: the mid-tibia is without long dense pale hairs (fig. 5C), and the apex of the mid-femur is without a pair of curved long hairs (fig. 5D).

Description. Male. Body length 7.5–8.0 mm, wing length 6.2–7.0 mm. Head: Face with strong black hairs, longer and denser in lower part, and covered with rather dense grey or golden tomentum, except the shining epistoma laterally and the matt central knob, which is weakly prominent and flattened medially. Face at level of central knob as wide as half of head width. Frons shiny, with fine tomentum and black hairs. Vertex dull, with black hairs on ocellar tubercle and pale hairs posteriorly. Occiput with pale hairs. Antenna entirely velvety black, including arista, postpedicel oval and rather small (fig. 5E). Thorax: Mesonotum slightly shiny, with dense, erect predominantly pale hairs, except black hairs on sides. Scutellum shiny, mostly with pale hairs, except longer and stronger black hairs on hind margin. Posterior anepisternum and anterior anepimeron moderately shiny, covered with long mainly black hairs. Katepisternum in lower part with dense tomentum and long robust black hairs. Wing membrane distinctly brownish, entirely covered with microtrichia. Legs: Coxae black, densely tomentose. Trochanters shining black. Fore-femur mainly yellow, with posterior black stripe, with subbasal tuft of two closely appressed long, wavy white hairs and 5–6 strong, long black bristles (fig. 5B). Ventral surface of fore-femur with long strong pale hairs and a few irregular black bristles. Fore-tibia distinctly broadened to apex, mostly yellow, paler posterodorsally, with black stripe in apical third anteroventrally (fig. 5A), laterally with yellow hairs. Foretarsus distinctly broadened, yellow, with short yellow hairs; fore-metatarsus ventrally with triangular black spot (fig. 5A); ventral surface of tarsomeres 2–5 dark medially. Mid-femur yellow anteriorly and black posteriorly; with 4–5 long black and yellow postero-ventral hairs in basal third; many comparatively long hairs on posterior side: yellow in basal half and black in apical half; ventral side with many strong short black bristles (fig. 5D), on tip without black hairs directed towards base of femur. Mid-tibia narrow in basal third and broadened in other part (fig. 5C), covered with short depressed yellow hairs; anterior and posterior surfaces without comparatively long yellow and black hairs. Tarsomeres 1–3 of mid-tarsus yellow, tarsomeres 4–5 darkened dorsally, hairs yellow. Hind femur black with yellow tip, antero-ventrally covered with rare hairs approximately as long as femur diameter, posterior surface with short semi-erect yellow hairs. Hind metatarsus black, distinctly swollen, broader on the middle than tibia; tarsomeres 2–3 brownish, tarsomeres 4–5 black. Abdomen: Terga entirely dull black or with traces of red marks (fig. 5F), often visible on tergum V, or with distinctly visible brownish oblong maculae on terga III–IV. Maculae on terga or their locations densely tomentose. Sterna densely tomentose, with long pale hairs.

Female. Body length 7.5–8.0 mm, wing length 6.8–7.0 mm. Head: Face dense tomentose, except facial tubercle and epistoma laterally, with pale hairs. Central knob weakly prominent, flattened medially. Frons shining black, with triangular maculae of grey pollen laterally. Thorax: Shining dorsally and densely tomentose laterally, with pale hairs, which are stronger between fore- and mid-coxae. Wing membrane weakly darkened, completely trichose. Fore- and mid-legs pale except black stripe on posterior surface. Fore-femur with tuft of long white hairs near base and with long sparse pale hairs posteriorly and ventrally; darkened surface with 1–2 long bristle-like hairs, basal 1/3 of ventral surface with 2–4 longer whitish hairs. Fore-basitarsus, tarsomeres 2 & 5 yellow, tarsomeres 3–4 darkened. Mid-femur with 3–5 long yellow hairs ventrally, their length equal to or longer than femur width; posterior surface with dense long hairs, white in basal 2/3 and black in apical third. Tarsomeres 4–5 of mid-tarsus darkened. Hind femur and tibia black with narrow yellow base and tip, covered with light hairs; hind basitarsus and tarsomeres 4–5 black, tarsomeres 2–3 yellow. Wings completely trichose. Abdomen completely black, shiny with fine brownish tomentum and short white hairs.

Etymology. The species is named from Beringia, the region surrounding the Bering Strait, the Chukchi Sea, and the Bering Sea.

Distribution. Russia: Chukotka.

Taxonomy. North American specimens from Colorado and Quebec, determined by J.R. Vockeroth as P. immarginatus, are similar to typical European specimens of P. immarginatus, but their mid-tibia is without distinct long pile. A specimen from Alaska, also determined by J.R. Vockeroth as P. immarginatus, is similar to P. beringiensis sp. n. in the hairs on the mid-legs, but its body coloration is paler.

In the keys to Far Eastern Platycheirus (Mutin in Mutin & Barkalov 1999), P. beringiensis sp. n. runs to P. immarginatus Zetterstedt, but differs in the following:

36. Bristles on posterior surface of fore-femur flattened apically and curved towards tip of femur.... P. mongolicus Stackelberg - Bristles on posterior surface of fore-femur rather straight and thinning evenly to tips.............................. 37 37. Abdomen black or with only reddish marks, mid-tibia without long dense pale hairs anteriorly (fig. 5C), mid-femur without

curved black hairs in apical part (fig. 5D), mid-tibia ventrally with black stripe in basal third (fig. 5A).. P. beringiensis sp. n. - Abdomen with large yellow spots, mid-tibia with long dense pale hairs anteriorly (fig. 5G), mid-femur with curved black hairs

in apical part, mid-tibia without black stripe in basal third................................. P. immarginatus Zetterstedt

In the key to Nearctic Platycheirus (Vockeroth 1990), P. beringiensis sp. n. goes to couplet 31 but differs in the following:

31. Tergites III and IV each with a pair of large yellow spots................................ P. immarginatus Zetterstedt - Tergites III and IV without large yellow spots, completely black or with a pair of silvery spots...................... 32 32. Fore femur with tuft of closely appressed long wavy white hairs. Fore tibia almost uniformly broadened from base almost to apex, without long black hair posteriorly (fig. 5B). Hairs of scutum and scutellum mostly yellow. Hairs of pleura black.......................................................................................... P. beringiensis sp.n. - Fore femur with subbasal tuft of 4 straight white hairs. Fore tibia strongly and abruptly broadened posteriorly at 3/4 length, with long black hair on posterior middle. Hairs of scutum and scutellum mostly black. Hairs of pleura all pale................................................................................................ P. s e t ip e s Vockeroth