Hesperinus electrus Skartveit, 2009: 5-7

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

Hesperinus electrus Skartveit, 2009: 5-7 Figs 1 , 12 , 13 , 14

Note.

The species was described based on a single, male specimen ( Skartveit 2009). One additional male specimen has turned up which shows details in wing venation and terminalia better than the type.

Holotype (male) SDEI Dip-00832 - CCHH #1093-1. Additional material (male) CCHH # 1789-1

Updated description of the species including type specimen

(some measurements from the holotype corrected): Total length 4.35-4.40 mm (N = 2). Colour dark brownish, body semi-matt, covered with short, coarse, dark hairs.

Head (Fig. 13 ): Length 0.47-0.52 mm (N = 2). Clearly dichoptic, complex eyes separated in frons by about the width of ocellar tubercle. Ocellar tubercle medium-sized, fairly prominent. Complex eye somewhat reniform, concave posteriorly, without apparent intraocular setae. Occiput with rather dense, short, dark pile. Antenna slender, about one and a half times as long as head, flagellum 0.78 mm long, 0.06 mm wide (N = 2), eight-segmented, all flagellomeres clearly longer than wide, with dark setae about as long as the width of the flagellomeres. Pedicel conical, pedicel and first flagellomere wider than the rest of flagellum. Palp brown, relatively long, last segment cylindrical. Mouthparts, apart from palp, not conspicuously developed.

Thorax: Length 0.90-0.92 mm (N = 2), width 0.55 mm (N = 1). Reddish brown with darker vittae around notaulix and anterolaterally at humerus, semi-matt, grayish pruinose, with sparse, short setae. Mesonotum with deep sulci. Pleura bare, densely grayish pruinose except for glabrous patches posteriorly on katepisternum and epimeron. Haltere brown.

Wing (Fig. 12 ) Length 4.18-4.35 mm (N = 2), width 1.32-1.52 mm (N = 2), length/width = 2.75-3.30 (wing of holotype may be slightly folded). Very slightly brownish fumose, membrane with very fine microtrichia, veins fine and brown throughout. Pterostigma not apparent. Costa with fine setulae about as long as width of vein, extends to nearly half-way between apices of R4+5 and M1. Humeral vein short and oblique. R2+3 rather long, oblique, basally bent. R4+5 strongly curved. R-M nearly vertical. M-veins apically very fine, hardly visible at wing edge, a little curved basad. CuA1 straight, CuA2 apically strongly curved basad. CuP fine, gently curved, reaches wing edge. Length of wing veins in mm (N = 2) subcosta 2.2-2.3, basal R 1.0-1.3, distal R1 1.5-1.6, Rs 0.45-0.55, R2-5 0.62-0.65, R2+3 0.75-0.91, R4+5 1.6-1.8, R-M 0.14, basal M 1.4, distal M 0.30-0.38, M1 1.8, M2 1.5-1.6, M-Cu 0.10-0.15, CuA 1.0-1.4, CuA1 1.7-2.0, CuA2 1.3-1.6.

Legs: Dark brown, long and slender, clad with strong, short, dark pile. Fore tibia with one, mid- and hind-tibiae with two short, straight, dark spurs. Tarsi very slender. Leg measurements (N = 2 unless otherwise stated) fore femur 1.4-1.5 mm long, fore tibia 1.4 mm long (N = 1), fore first tarsomere 0.77 mm long (N = 1), mid femur 1.5 mm long (N = 1), mid tibia 1.3 mm long (N = 1), hind femur 1.6-1.9 mm long, 0.12 mm wide (N = 1), hind tibia 1.8-2.1 mm long, 0.09 mm wide (N = 1), hind first tarsomere 0.86 mm long (N = 1).

Abdomen: Dark brown, cylindrical, slender, rather densely clad with dark brown pile. Length 3.1 mm, width 0.5 mm (N = 1).

Terminalia (Fig. 14 ): Width of hypopygium 0.47 mm (N = 1). Hypopygium slightly expanding apicad, clad with short, dark pile. Gonostylus curved and sharply pointed, 0.24 mm long (N = 1). Posterior edge of gonocoxosternite almost straight. Epandrium apparently quite small, not possible to see clearly, probably rounded-rectangular. Ejaculatory apodeme large and prominent, apically dome-shaped.

Discussion.

The original description was found to contain some errors, e.g., the flagellum has eight, not seven segments, and is shorter than stated in the description. The poorly developed mouthparts suggest that this species did not feed in the adult stage, this may be a general trait for Hesperinus species as all seem to have very small mouthparts. The genus Hesperinus has frequently been referred to a separate family, the Hesperinidae (e.g., Krivosheina 1997). However, molecular evidence suggests that the genus belongs in the Bibionidae ( Ševčik et al. 2016) and this is also supported by fossil material, where Hesperinus and Penthetria species look far more similar than in the modern species. Hence, I prefer to place Hesperinus and Penthetria together in the subfamily Hesperininae in Bibionidae ( Skartveit and Ansorge 2020).

Figures

Figure 1. Hesperinus electrus, male. CCHH 1789.1. Photo: Christel and Hans-Werner Hoffeins.

Figure 12. Hesperinus electrus, male, wing. Scale bar: 1 mm.

Figure 13. Hesperinus electrus ¸ male, head. Scale bar: 0.1 mm.

Figure 14. Hesperinus electrus, male, terminalia. Scale bar: 0.1 mm.