Bibio succineus, Skartveit, 2021

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

Bibio succineus sp. nov. Figs 8 , 24 , 25 , 26 , 27 , 28

Type material.

Holotype (male), SDEI Dip-00900 - JS-Baltic-009. The specimen is preserved in a piece of yellowish amber, 30 ×17× 6 mm. Syn-inclusion: one sciarid gnat.

Additional material

(female) Coll. Kernegger 59/2006. The specimen was briefly described by Skartveit (2009: 26-27).

Comparison to other species.

Four species of Bibio have been described from the Eocene/Oligocene of Isle of Wight ( Krzeminski et al. 2019). Of these, Bibio gurnetensis Cockerell, 1917 and Bibio oblitus Cockerell, 1921 both have crossvein R-M much longer than the basal Rs, this character suggests the species belong in the genus Dilophus , though, not having seen the original material, I will not make a formal transfer here. Bibio extremus Cockerell, 1921 differs from the present species in that the basal part of Rs is quite steep and that crossvein M-Cu meets M2 considerably distally of furcation. Bibio oligocenus Cockerell, 1917, which despite the name was described from the late Eocene, differs from the present species by being larger (wing length 8 mm) with a conspicuously darkened costal cell in the wing.

Etymology.

The epithet is derived from Latin succinum, amber, referring to the preservation of the type specimen. It is the first species of the genus Bibio described from amber fossils.

Diagnosis.

A medium-sized Bibio , body length about 7.5 mm. Body and legs entirely black, densely pilose, pile on thorax and abdomen pale, black on legs. Antennal flagellum 8-9-segmented. Haltere pale brown. Wing light brownish fumose in male, brown fumose in female, pterostigma pale and indistinctive, radial sector about four times as long as R-M. Fore tibia with spur a little less than half as long as spine. Hind tarsus not enlarged.

Description.

Male (N = 1): Total length 7.5 mm, entirely black.

Head (Fig. 25 ): Length 1.37 mm, width not possible to measure. Complex eye with rather dense, pale, fine, medium-length intraocular pile. Ocellar tubercle not prominent, with short, dark setae. Rostrum not prominent. Antenna: flagellum 8-segmented, 0.53 mm long, 0.13 mm wide. Two distal palp segments slender (more basal segments not possible to see).

Thorax: Length 2.2 mm, black, very shiny. Pile pale, anteriorly rather short, getting longer in posterior part, sides of mesonotum and pleurae with long but rather sparse, pale pile. Sides of mesonotum with rather coarse, mesh-like microsculpture. Scutellum rounded with long, pale, proclinate setae along edge. Meron very shiny, in upper corner with about 20 long, pale hairs. Haltere pale brown, not possible to see well.

Wing (Fig. 24 ): Length 5.6 mm, width 1.9 mm, length/width = 2.92. Slightly brownish fumose, Costa and R1 light brown, posterior veins colourless. Pterostigma pale brown, inconspicuous, 0.45 mm long, 0.15 mm wide. Membrane without conspicuous microtrichia. Costa extends to apex of R4+5. Humeral vein present, fine and oblique. Subcosta weak, visible only in distal part. Basal radial sector about four times as long as crossvein R-M, M curves towards R1 at R-M. M basally clearly connected to CuA. M-Cu oblique, meets M at furcation. CuA1 apically moderately, CuA2 strongly curved basad. Vein lengths, all in mm: Basal R 2.51, distal R1 1.20, Rs 0.39, R4+5 2.63, R-M 0.09, basal M 1.80, distal M 0.94, M1 1.95, M2 1.73, M-CuA 0.38, CuA 1.13, CuA1 2.51, CuA2 1.91.

Legs: Black, clothed with short, strong, dark setae. Fore tibia (Fig. 26 ) with spur about half as long as spine. Hind femur (Fig. 28 ) basally thin, expanding at about ¼ of length, outer part stocky. Hind tibia rather slender, densely pilose, apparently without bare field of sensillae. Tarsus slender. Fore femur length 1.24 mm, width 0.32 mm, hind femur length 2.29 mm, width 0.41 mm, hind tibia length 2.25 mm, width 0.26 mm, hind first tarsomere 0.63 mm long, 0.18 mm wide, hind second to fifth tarsomeres length 0.38, 0.28, 0.23, 0.37 mm.

Abdomen: Black, clothed with rather short, fine, pale pile.

Terminalia: Gonostylus apically slender, rather straight. Hypopygium otherwise not possible to see.

Female (tentatively associated, N = 1): Total length 7.5 mm, entirely black.

Head: Antennal flagellum 9-segmented. Occiput with short, dark setae. Complex eye rather small, rounded, with short, scattered, brownish intraocular pile.

Thorax: Mesonotum length 1.9 mm. Covered by Verlumung in the specimen available. Haltere yellowish.

Wing: Brown fumose, membrane without microtrichia. Costa and R-veins brown, more posterior veins colourless. Basal radial sector about five times as long as crossvein R-M

Legs: black, rather stout. Length of fore femur 1.5 mm, width 0.5 mm, length of fore tibia 1.4 mm, of hind tibia 2.2 mm. Fore tibia (Fig. 27 ) with spine about three times as long as spur, this is stout, straight and pointed. The tibia is clothed with quite long, fine setae and has a field of rounded coeloconical sensillae in the middle of the anterior face. The tarsi are quite slender.

Abdomen: cylindrical, no details possible to see.

Terminalia: no details possible to see.

Figures

Figure 8. Bibio succineus sp. nov., holotype, male. JS-Baltic- 009. Photo: Marius Veta.

Figure 24. Bibio succineus sp. nov., male, wing. Scale bar: 1 mm.

Figure 25. Bibio succineus sp. nov., male, head and thorax. Scale bar: 1 mm.

Figure 26. Bibio succineus sp. nov., male, fore tibia. Scale bar: 1 mm.

Figure 27. Bibio succineus sp. nov., male, hind leg. Scale bar: 1 mm.

Figure 28. Bibio succineus sp. nov., female, fore leg. Scale bar: 1 mm.