Spilogona contractifrons

Taxonomic analysis of ‘ Spilogona contractifrons species-group’

Flies of this group of species can be distinguished as follows: scutum with 3 post dc setae, mid tibia without pv and with 1 ad seta, fore tibia with 1 p seta, hind femur with a row of pv setae, mid femur with anterior preapical seta, haltere yellow, facial edge not projecting beyond level of profrons, prementum shining, scutellum without downwardly-directed preapical setulae on upper border of declivities, abdomen plump, katepisternal setae arranged in a more or less equilateral triangle like Coenosia Meigen, 1826.

Four species of this group are currently recognised: the widespread S. alticola, S. arctica, S. contractifrons, and the East Asian S. orthosurstyla. Research for the current paper has included a detailed study of extensive material from the territory of Russia, from both tundra zones and mountain areas, and personal study of the bulk of Huckett’s collection deposited in the Canadian National Collection, Ottawa, Canada.

The study of extensive material has confirmed the existence of four species in this group. Despite the difficulties in the recognition of species of this group, there are several helpful diagnostic characters: the shape of male sternite 5, the shape of male terminalia, and the colour of the scutum (Figs 1–2, Table 1). The colour of the scutum can be variable in different populations but the shape of the male sternite 5 is constant and is clearly visible in dry specimens (Fig. 1 G–I).

At present it is impossible to separate females of these species. Males can be distinguished by the following couplets:

1. Scutum completely dark brown (mountain populations) or light grey with indistinct stripes (arctic tundra populations); sternite 5 with a narrow median notch (Fig. 1E, H), with a wavy inner edge; in lateral view hypandrium with a protuberance; surstylus sharply curved at middle (Fig. 1K)..................................................................................... S. arctica (Zetterstedt, 1838)

¯ Scutum grey or brownish dusted with more or less distinct dark stripes; sternite 5 with a rather wide median notch; hypandrium without a distinct protuberance; shape of surstylus not as above......... 2

2. Sternite 5 with a wide rectangular median notch, inner edge more or less straight (Fig. 1F, I); scutum with distinct dark stripes; surstylus short, gently curved, about as long as cerci (Fig. 1L)................................................................................................... S. alticola (Malloch, 1920)

¯ Sternite 5 not as above; scutum with indistinct dark stripes, often diffuse; surstylus longer than cerci................................................................................................................................................... 3

3. Sternite 5 with an extended and pointed caudal margin (Fig. 2C); surstylus straight, curved only at apex (Fig. 2A).............................................................................. S. orthosurstyla Xue & Tian, 1988

¯ Sternite 5 with a rounded caudal margin (Fig. 1D, G); surstylus not straight, weakly curved at middle (Fig. 1J)..................................................................................... S. contractifrons (Zetterstedt, 1838)