Dilophus bicolor Wiedemann 1821
Creators: name: Skartveit, John
name: Freidberg, Amnon
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Bibionidae
Dilophus
Dilophus bicolor

description: Dilophus bicolor Wiedemann, 1821 (figs. 24–25, 119–126)
syn Philia splendens Hardy, 1951 (syn. n.)
Type locality: REPUBLIC OF SOUTH AFRICA, ́ Cape ».
Syntypes (female) ZMUC 00024824 and 00024825.The former is in perfect condition, in the latter, the antennae, the right mid leg and the terminal segments of both fore tarsi and the right hind tarsus are missing, and the colour appears to be a little faded, otherwise it is in good condition. Holotype and paratype Philia splendens (♁ and ♀ in copula), REPUBLIC OF SOUTH AFRICA, ́ Cape Province, Somerset East, Nov. 25–30, 1930 », ́ Holotype » (circular label with red egde), ́ Allotype » (circular label), ́ PHILIA /splendens/ det. 1948 Hardy/ D.E. Hardy», ́BNMNH (E) #/ 252970», ́NHMUK 014427894 (with barcode)».
Other material: REPUBLIC OF SOUTH AFRICA, KwaZulu-Natal, Royal Natal National Park, 4 ♁♁ 3 ♀♀ (NMSA), Royal Natal National Park, Drakensberg, Bergville Div., Tugela Gorge, 1830m, 27.xi.1951, 1 ♀ (NHMUK), Cape Peninsula, Roberston Pass nr. Mossel Bay, 610m, 1.ix.1932, R.E. Turner leg., 1 ♀ (NHMUK).
Previous records: Republic of South Africa (Wiedemann 1828, Hardy 1951a).
Diagnosis: The species is easily distinguishable from all other species except D. buxtoni by its large size (5.5–7 mm). From females of the latter species in can be recognised by the black legs, thorax reddish-orange with spines black.
Male (fig. 24): Relatively large, dark-winged, densely pilose
Total length 5.6–7.0 mm (N=3).
Head (fig. 120): Length 0.87–1.19 mm, width 1.08–1.23 mm (N=3). Black, shiny. Ocellar turbercle rather prominent. Intraocular pile dense, rather long, brownish, Rostrum extending about half diameter of lower complex eye in front of complex eye. Antenna black, flagellum 0.40–0.49 mm long, 0.08–0.11 mm wide (N=3), cylindrical, 9-segmented, terminal three segments close-set. Palp quite short, black, terminal segment conical. Occiput with long, forward-curving, black setae. Venter with long, dense, grayish setae.
Thorax: Length 1.55–1.91 mm, width 0.92–1.36 mm (N=3). Black, shiny. Pronotal spine row with 8 slender spines placed on transverse comb. Mesonotal spine row with 10 short spines forming a transverse row, 4–5 spines on each side more posteriorly, rather widely spaced, the posterior nearly on level with wing base. Acrostrichal area bare, dorsocentral setae strong, rather dense, erect, blackish. Pronotum and mesonotum laterally with long, quite dense, dark pile. Haltere dark brown.
Legs: Entirely black with relatively dense, grayish pile. Fore tibia (fig. 121) sligthly expanding apicad, mesally with 3 slender spines forming a slightly oblique row, apically with 8 slender spines in circlet. Mid tibia without spine-like setae. Hind femur quite strongly clavate. Hind tibia slender, basally with some long setae forming a ventral row. First hind tarsomere slightly enlarged. Measurements (N=3 unless otherwise stated): fore femur 0.96–1.23 mm long, 0.32–0.41 mm wide, fore tibia 1.00– 1.34 mm long, 0.17–0.19 mm wide, first fore tarsomere 0.81–0.98 mm long, mid femur 1.25–1.40 mm long (N=2), mid tibia 1.13–1.32 mm long (N=2), hind femur 1.70–1.94 mm long, 0.34–0.40 mm wide, hind tibia 1.66–2.13 mm long, 0.19–0.26 mm wide, first hind tarsomere 0.58–0.79 mm long.
Wing (fig. 119): Length 4.48–5.15 mm, width 1.62–2.06 mm, length/width = 2.50–2.79 (N=3). Blackisk-brown fumose, costal cell a little darker. Pterostigma dark brown, moderately distinctive. R-veins and stem of M dark brown, posterior veins brown, all veins strong and distinctive. Costa with fine setules, extending a little beyond apex of R 4+5. Humeral vein absent. Subcosta distinctive, straight, membrane between Subcosta and R paler than rest of wing. R 1 pigmented to apex, terminates at middel of pterostigma. Rs nearly half the length of crossvein R-M. R 4+5 gently curved. Stem of M rather strong, weaker beyond R-M. Fork of M asymmetrical, M 1 basally rather weak, bent, often with short appendix vein at bend. M-veins apically gently curved. M-Cu meets M considerably before furcation, distance from fork roughly equal to the length of the crossvein, M with a little kink at junction with MCu. CuA with rather long stem and short, wide fork. CuA 1 with a small kink at M-Cu. Both CuA-veins, particularly CuA 2, apically curved basad. CuP very weak and indistinctive, but apparent as a fold. A 1 basally fairly distinctive, but not reaching apex of wing.
Abdomen: Black, shiny, densely clad with strong, erect, blackish setae.
Terminalia: Hypopygium (fig. 122–123) width 0.57–0.74 mm (N=3), almost quadrate in outline. Gonostylus 0.30–0.40 mm long (N=3), strong and curved, apically with a deep notch just below tip, densely setose, dorsally with long, grayish setae. Epandrium relatively small, trapezoidal, apically strongly convex. Gonocoxites with strong and dense, curved, blackish setae both dorsally and ventrally. Ventral indentation of gonocoxosternite rather wide, v-shaped. Gonocoxite ventro-apically with a rounded, mesal projection.
Female (fig. 25):
Total length 4.6–5.2 mm (N=3).
Head (fig. 125): Length 1.09–1.26 mm (N=3), width 0.77–0.80 mm (N=2). Black, moderately shiny with reticulate microsculpture.Relatively long and narrow, a little more than twice as long as complex eye. Ocellar tubercle small and quite prominent. Complex eye fairly prominent, rounded. Frons flat, nearly naked. Head posteriorly with short, dark pile. Antenna black, flagellum 0.45–0.51 mm long, 0.10–0.11 mm wide (N=3), cylindrical, 9-segmented. Palp short, black, terminal segment a little conical. Head extending c. 0.8* eye diameter in front of complex eye, but not further than antennal base.
Thorax: Length 1.98–2.21 mm, width 1.10–1.13 mm (N=3). Orange-red, shiny, spines black. Pronotum laterally with numerous setae, otherwise nearly bare. Pronotal spine row with 12–14 short spines on transverse comb. Mesonotal spine row quite irregular, with about 14 short (length fairly variable), irregularly spaced spines froming a transverse arch, 2 spines more posteriorly on each side. Haltere dark brown.
Legs: Coxae and femorae orange-red, tibia and tarsi black. Pile moderately dense, long and blackish. Fore tibia (fig. 126) distinctively expanding towards apex, mesally with 3 prominent, long spines on slightly oblique row. Apical circlet with 8 long spines. Mid tibia with 4–5 strong setae dorsally, apically with circlet of 4 distinctive but not spine-like setae. Hind tibia slender, all tarsi very slender. Measurements (N=3): fore femur 0.92–1.06 mm long, 0.36–0.42 mm wide, fore tibia 1.02–1.08 mm long, 0.19–0.21 mm wide, first fore tarsomere 0.79–0.96 mm long, mid femur 1.21–1.36 mm long, mid tibia 1.21–1.25 mm long, hind femur 1.70–1.79 mm long, 0.32–0.34 mm wide, hind tibia 1.79–1.96 mm long, 0.21–0.25 mm wide, first hind tarsomere 0.72–0.87 mm long.
Wing (fig. 124): Length 5.52–6.19 mm, width 2.17–2.40 mm, length/width = 2.53–2.58 (N=3), colour and venation as in male.
Abdomen: Cylindrical, dark brown to black, shiny, clad with relatively long, grayish pile.
Terminalia: Cerci black, a little clavate.
Distribution and ecology: The species is distributed in the southern part of the Republic of South Africa north to the Drakensberge monutains. Information on altitude is sparse but the species has been found at least at altitudes between 600–1800m.
Flight period: The species has been recorded in September–November, that is, in late spring (Table 2).
Discussion: The holotype of Dilophus bicolor (http://daim.snm.ku.dk/digitaliseret-typesamling-detaljer-enkelvisning?catno=zmuc00024825) fits rather well Hardy (1951)’s description of Dilophus splendens. Contrary to Hardy’s description, there is no significant difference in thorax colouration or head length, and the brown (as opposed to black) abdomen of the Dilophus bicolor type is likely due to fading of an old specimen, this may also be the reason for the reported differences in pile colouration. The two species were supposed to differ in the extent of the Costa, terminating at one-fourth the distance between apices of R 4+5 and M 1 in Dilophus splendens and one-third this distance in D. bicolor, however this difference is almost certainly within the range of individual variability.
description: Published as part of Skartveit, John & Freidberg, Amnon, 2023, Revision of the genus Dilophus Meigen, 1803 (Diptera, Bibionidae) from the Afrotropical Ecozone, pp. 301-354 in Zootaxa 5360 (3) on pages 334-345, DOI: 10.11646/zootaxa.5360.3.1, http://zenodo.org/record/10152307