Dilophus atrimas Edwards, 1915

Skartveit, John & Freidberg, Amnon, 2023, Revision of the genus Dilophus Meigen, 1803 (Diptera, Bibionidae) from the Afrotropical Ecozone, Zootaxa 5360 (3), pp. 301-354 : 315-317

Dilophus atrimas Edwards, 1915 ( Figs. 11–12 , 69–76 )

Type locality: KENYA, Mount Kenya, 3200–3700 m.

Type supposed to be in NHMUK (not found by first author and also not by Hardy (1951)), also 1 ex. labeled as type in MNHN.

Syntypes (according to Edwards 1915: 61): KENYA, Mt. Kenya , alpine prairies, 3300–3700 m., st.no. 43, 30.i. 1912, C. Alluaud & R. Jeannel leg

Previous records: Kenya ( Edwards 1915)

Additional material: KENYA, Mt. Kenya , alpine zone, 3785 m (1), 3800 m (3), 4350 m (1), 21.–23.vii. 1981, Lars Fröberg leg., 1 ♁ 4 ♀♀ ( MZLU) , Mt. Kenya, N. side, Siramar track, 3260m, 20.22– xii. 1980, P.S. Cranston leg, 1 ♁ 1 ♀ ( NHMUK) , 3300–3600m, 1♁ ( NHMUK) , Mt. Kenya , Naru Moru, 3300m, from Lobelia keniensis , 28.viii. 1949, J.A. Riley leg., 1♁ 18♀♀ ( NHMUK) , Mt. Kenya , 4450m, 15–16.ii. 1936, 8 ♁♁ 3 ♀♀ ( NHMUK) . TANZANIA, Mt. Meru , 4000 m, xii. 1925, F. Bryk leg., 3 males ( UZMH) .

Diagnosis: A relatively large (4–5.5 mm) and robust, entirely black species, head, thorax and legs with long and dense pile. The species is easily recognisable on account on the dense pile, more reminiscent of the genus Bibio than of typical Dilophus .

Description:

Male (fig. 11) (N=1): Total length 5.7 mm.

Head (fig. 70): Length 1.15 mm, width 1.15 mm. Complex eye with dense, long (about 0.3 mm), erect, yellowish intraocular setae. Occiput with dense, dark, proclinate setae. Underside of head with long, proclinate, dark pile. Ocellar tubercle rather small, not prominent. Rostrum not at all produced beyond margin of complex eye. Palp rather small, black with long setae, relatively slender, last segment cylindrical. Antenna entirely black, flagellum 0.45 mm long, 0.10 mm wide, 9-segmented, flagellomeres robust with short but strong setae.

Thorax: Length 1.66 mm, width 1.22 mm. Entirely black, moderately shiny due to strong microsculpture. Pronotal spine comb with 12 rather short, sharp, reddish spines. Mesonotal spine row with approximately 14 short spines. Mesonotum with long, grayish, inclinate dorsocentral setae, irregular in anterior part, uniseriate posteriorly. Pronotum and sides of mesonotum with abundant, long, setae, mostly inclinate. Scutellum with dense, coarse but not particularly long, greyish marginal setae. Pleura with fairly sparse but long, grayish setae. Pleura and sides of mesonotum with strong, reticulate microsculpture, dorswal part of meron with strong. Longitudinal microsculpture. Haltere brownish-black.

Legs: Entirely black. Femorae moderately clavate with long, fine, grayish setae, about twice as long as femur width, tibiae and tarsi slender with long, erect, grayish pile. Fore femur 0.90 mm long, 0.27 mm wide, fore tibia (fig. 71) 1.00 mm long, 0.13 mm wide, with 3–4 mesal spines (according to original description) usually arranged 2–3 in an oblique row and 1 a little more distal), apical spine circlet with 8 spines (7–9 according to original description). Fore first tarsomere 0.48 mm long, 0.11 mm wide, mid femur 1.00 mm long, mid tibia 1.05 mm long. Hind femur 1.50 mm long, 0.23 mm wide, hind tibia 1.58 mm long, 0.16 mm wide, hind first tarsomere 0.37 mm long, 0.08 mm wide.

Wing (fig. 69): Length 4.7 mm, width 1.7 mm, length/width = 2.7. Hyaline with rather strong and dense microtrichia. Anterior veins fine, dark brown, posterior veins almost colourless. Pterostigma oblong, yellowish-brown, distinctive. Costa basally with long, dense, dark setulae, more distally with strong setulae about twice as long as width of costa. Costa extends to a little past half-way between apices of R 4+5 and M 1. Humeral vein absent. Subcosta basally rather wide, yellowish, fading apicad, apically scarcely visible. R s a little over half as long as R-M. R 4+5 fine, gently curved. M basally connected to CuA, fine, pigmented until R-M. Fork of M asymmetrical, M-M 2 forms a straight line and M 1 diverges forward from this. The fork is relatively narrow and M 1 and M 2 are parallel apically. M-Cu is rather indistinctive, meets M at furcation. Fork of CuA short and wide. CuA 1 slightly kinked at M-CuA, strong and distinctive to wing edge. CuA/CuA 2 wide, colourless, CuA 2 apically almost straight. CuP visible basally only. A 1 visible as a small, angular vein around anal angle.

Abdomen: black, shiny, with fairly abundant, long, pale yellowish pile.

Terminalia: Hypopygium (figs. 72–73) rounded, moderately pilose, with fine and pale setae. Gonostylus short, straight, subcylindrical, blunt, moderately pilose. Epandrium wide, rounded, posteriorly concave, rather densely clad with long setae. Gonocoxosternite with a narrow, rectangular indentation, densely clad with setae which are finer than dorsally.

Female (fig. 12) (N=4):

Total length 4.2–5.4 mm. Head and thorax black, shiny, legs and abdomen chestnut-brown. All parts with relatively long, abundant, pale pile.

Head (fig. 75): Length 0.85–0.88 mm, width 0.62–0.78 mm. Complex eye rather prominent, rounded, about one half of head length, head extends about equally long behind and ahead of it, with sparse but relatively long intraocular pile (about 0.05 mm). Frons and occiput with dense, long, yellowish pile. Ocellar triangle rather small, not prominent. Antenna entirely black, flagellum 0.43–0.45 mm long (N=2), 0.12–0.13 mm wide, robust, apically conical, 9-segmented. Palp slender.

Thorax: Length 1.85–1.94 mm (N=3), width 0.90–1.05 mm. Pronotal spine comb with 12 short, reddish spines, mesonotal spine row with about 16 short spines. Setae approximately as in male but a little shorter, less dense and paler. Pleural microsculpture as in male.

Legs: Chestnut-brown with long, yellowish pile which is consiberably longer than width of the segment. Protibial spines (fig. 76) short, strong, a little blunt, pattern as in male. Measurements: fore femur 0.72–0.85 mm long, 0.30–0.37 mm wide, fore tibia 0.83–0.98 mm long, 0.12–0.15 mm wide, fore first tarsomere 0.50–0.53 mm long, 0.08–0.10 mm wide, mid femur 0.95–0.98 mm long, mid tibia 0.93–1.02 mm long, hind femur 1.35–1.52 mm long, 0.22–0.28 mm wide, hind tibia 1.45–1.58 mm long, 0.13–0.18 mm wide, hind first tarsomere 0.48–0.53 mm long, 0.08–0.12 mm wide.

Wing (fig. 74): Length 5.2–5.8 mm, width 1.7–2.1 mm, length/width = 2.7–3.0. Slightly yellowish-brown, almost hyaline. Venation as in male.

Abdomen: Cylindrical, shiny, dark chestnut-brown with pale pile.

Terminalia: Cerci black, elongate, slightly expanded apicad, with dense, long, yellow pile. Last sternite mesally with wide, V-shaped, yellowish-brown, membraneous area, apically pointed.

Distribution and ecology: The species is only known from the Kenya and Meru mountains and lives in the alpine zone, being found at altitudes between 3260–4450 m. The specimens from 4450 m is the highest altitude record for the family Bibionidae in Africa. The species has been found in number on Lobelia keniensis , and also on buffalo dung. The conspicuous, long and dense pilosity is probably an adaptation to low temperatures.

Flight period: The available specimens have been collected in July–August, and between December–February ( Table 2 ).

Figures

FIGURES 11–14. 11. Dilophus atrimas Edwards, 1915, male, habitus. 12. Dilophus atrimas Edwards, 1915, female, habitus. 13. Dilophus capensis Edwards, 1925, male, habitus. 14. Dilophus capensis Edwards, 1925, female, habitus.

FIGURES 69–73. Dilophus atrimas Edwards, 1915. 69. Male, wing. 70. Male, head and thorax. 71. Male, fore tibia. 72. Male, terminalia, dorsal. 73. Male, terminalia, ventral.

FIGURES 74–76. Dilophus atrimas Edwards, 1915. 74. Female, wing. 75. Female, head and thorax. 76. Female, fore tibia.