Diamesa

Diamesa sp.

" Diamesa chorea Lundb. (?)" sensu Lundström (1915: 22), not Lundbeck, 1898: 291. (Fig. 23)

Material examined. RUSSIA: Chara­Ullach Mts., Lake Ketalach, 1 Ψ, 21. vii. 1902, M. I. Brussnew.

FEMALE IMAGO (n = 1)

Total length 5.63 mm. Wing length 4.34 mm long. Total length/wing length 1.30. Wing length/length of profemur 2.85. Coloration brown.

Head. Eyes bare. AR 0.63. Pedicel with 1 strong setae. Lengths of flagellomeres (in m) as: 88, 56, 68, 49, 60, 199. Third flagellomere with deep sensilla capitata, last flagellomere with 2 apical setae each 86 m long. Coronal suture complete. Temporal setae 29, consisting of 19 frontals and inner verticals, 4 outer verticals, and 6 postorbitals.

Clypeus with 17 setae. Tentorium 263 m long, 56 m wide, anterolateral process (sieve pore) weak; stipes 244 m long, plate 135 m wide. Palpomere lengths (in m):68, 109, 184, 161, 255.

Thorax. Antepronotum with 7 setae. Acrostichals absent, dorsocentrals 12, prealars 12. Scutellum with 24 setae in two rows.

Wing. VR 0.97. Brachiolum with 5 setae, R with 17, R1 with 20, R4+5 with 23 setae, other veins bare. R4+5 with campaniform sensilla. Alula with 6 setae. Squama with 51 setae.

Legs. Spur of front tibia 90 m long, spurs of mid tibia 79 and 71 m long, of hind tibia 113 and 75 m long. Width at apex of front to hind tibiae (in m) as 71, 75, 90. Pseudospurs 49–60 m long, present on ta1 and ta2 of all legs, with 9 additional spine­like setae present along ta1 of mid leg, 4 on ta2 of mid leg, and 5 on ta2 of hind leg. Sensilla chaetica about 280, at 0.12–0.96 of length from base of hind ta1. Fourth tarsomere slightly cordiform. Lengths (in m) and proportions of legs:

Abdomen. Tergite VIII with about 30 setae. Sternite VIII with 26 setae.

Genitalia (Fig.23). Gonocoxite with 11 setae. Tergite IX not clearly divided, with about 45 setae. Cercus 195 µm long. Seminal capsule ovoid, with anterior nipple, 135 µm long including neck, 68 µm wide. Spermathecal duct short, with bend, but no loop. Notum 206 µm long. Flap (Willassen 1985, fig. 5.2, 5.3) covering most of ventrolateral and all of dorsomesal lobe.

Remarks

Diamesa chorea Lundbeck was originally described from Greenland. According to Hansen & Cook (1976: 74/75), the male of D. chorea differs from D. bertrami Edwards, 1935 only in having bare eyes, the hypopygia being identical. The present female specimen, although with bare eyes, has genitalia quite different from those of D. bertrami as described by Willassen (1982). Willassen described and gave a key to the females of 37 species of Diamesa Meigen. The present specimen keys to Diamesa incallida (Walker) in Willassen (1982) resembling in having bare eyes, R4+5 with campaniform sensilla, pseudospurs present on front leg, numerous sensilla chaeticae distributed at least to 0.9 of hind metatarsus, all leg measurements and ratios nearly identical, weakly divided T IX, well developed flap, and nearly straight spermathecal ducts. It differs, among other, in having less distinctly cordiform ta4, well developed nipple on the seminal capsule, and posterior margin of flap not perpendicular to mesal line.