Dilophus sp.

Skartveit, John, 2021, A new fossil species of the genus Bibio, with an update on bibionid flies from Baltic and Rovno amber (Diptera, Bibionidae), Deutsche Entomologische Zeitschrift 68 (1), pp. 81-99 : 81

Dilophus sp. Figs 10 , 11 , 32 , 33 , 34

Previously examined material.

female, MHNN 711.

Material, females.

JS-Baltic-010, in piece of amber 20 ×12× 5 mm; JS-Baltic-011, in piece of amber 29 ×17× 3 mm.

Two female specimens, belonging to the Dilophus febrilis -group, with 9 flagellomeres, so not fitting any of the previously described species which have 6-7 ( Dilophus crassicornis ) or 12 ( Dilophus pseudofebrilis and Dilophus succineus ) flagellomeres. They are likely to be conspecific with the poorly preserved specimen treated as Dilophus sp. by Skartveit (2009: 38). As the other species of Dilophus from Baltic amber are based on male specimens I find it not advisable to formally name this species at the present stage of knowledge. Males of this species, should they appear, should be recognizable by characters of the antenna and fore tibia.

Total length 4.55-5.68 mm. Body and legs entirely dark brown.

Head (Fig. 33 ): Length 0.68-0.80 mm. Occiput, frons and gena all with strong, erect, relatively dense setae. Complex eye about half as long as head, somewhat protruding, with short and fine, rather dense intraocular pile. Ocellar triangle rather tall. Flagellum 9-segmented, 0.35-0.40 mm long, 0.06-0.08 mm wide. Palp shorter than antenna, with last segment conical, about 2.5 times as long as wide, bearing relatively long setae.

Thorax: Length 1.42-1.52 mm (N = 2), width 0.93 mm (N = 1). Pronotal spine comb with 12 evenly spaced, medium-length, erect, sharp spines. Mesonotal spine comb with about 16 small, sharp spines. Mesonotum moderately shiny with uniserial, short and fine dorsocentral setae (about 15 on each side), otherwise mostly bare. Scutellum evenly clothed with fine, short setae. Haltere dark brown with pale stem.

Legs: Black with medium-length, dark setae. Protibia (Fig. 34 ) with four sharp, semi-erect mesal spines, the two most basal ones close-set, the two more distal separated by about one spine length. Apical circlet with eight sharp spines. Mid and hind legs slender throughout. Fore femur 0.63-0.72 mm long, 0.23 mm wide (N = 2), fore tibia 0.75 mm long, 0.10 mm wide (N = 1). Mid femur 1.03 mm long (N = 1). Hind femur 1.13-1.57 mm long (N = 2), 0.17-0.18 mm wide (N = 2), hind tibia 1.12-1.60 mm long, 0.08-0.12 mm wide, hind first tarsomere 0.41-0.53 mm long, 0.05 mm wide.

Wing (Fig. 32 ): Rather crumbled in the newly acquired specimens. The specimen studied by Skartveit (2009) with wing as in Fig. 32 , wing length 4.4 mm. Almost hyaline, costa and R-veins dark brown, more posterior veins lighter brown but still distinctive. All veins are fine, no conspicuous thickenings. Costa with biseriate, rather dense, pale setulae, basally about as long as the width of the costal cell, decreasing in length apicad. Costa extends to about half-way between apices of R4+5 and M1. Pterostigma oval, brown, distinctive. Humeral vein present, subcosta fine, straight, running well separated from R 1 in entire length. Basal R and R1 dorsally with uniserial, fine, dark setulae which are about as long as the width of the vein and separated by about as much as their length, veins otherwise bare. Radial sector about one-third the length of crossvein R-M. R4+5 gently curved. Area between R4+5 and M1 about 1.5 times as wide as fork of M. M-veins apically straight. Crossvein M-CuA meets M well basad of furcation. CuA with rather long stem and short fork, CuA2 apically a little curved basad. CuP running approximately parallel to CuA, rather indistinctive. A1 apparent on stem of wing only.

Abdomen: Strongly swollen in specimen at hand, membraneous areas stretched. This is presumably because it is egg-filled. Tergites and sternites clad with short, dark setae.

Figures

Figure 10. Dilophus sp., female. JS-Baltic- 010. Photo: John Skartveit.

Figure 11. Dilophus sp., female. JS-Baltic- 011. Photo: Jonas Damzen.

Figure 32. Dilophus sp., female, wing. Scale bar: 1 mm.

Figure 33. Dilophus sp., female, head. Scale bar: 0.1 mm.

Figure 34. Dilophus sp., female, fore tibia. Scale bar: 0.1 mm.