Plecia maimensis Gentilini, 1993

Skartveit, John & Nel, André, 2017, Revision of fossil Bibionidae (Insecta: Diptera) from French Oligocene deposits, Zootaxa 4225 (1), pp. 1-83 : 53-55

Plecia maimensis Gentilini, 1993

(Figs. 45 – 46, 149 – 153)

Plecia maimensis Gentilini, 1993: 158 .

We have not studied the type of this species. It is possibly a synonym of Plecia livida , but this is uncertain. Unique among fossil bibionids, this species was described from a male and female specimen in copula, thus the association of male and female is less tentative than in the other fossil species.

Material (tentative) Males: RGL Bois d’Asson 3, Bois d’Asson 24, Bois d’Asson 85, Bois d’Asson 90, Bois d’Asson 122, Bois d’Asson 139, Bois d’Asson 179.

Females: RGL Dauphin 1, Dauphin 2, Bois d’Asson 4, Dauphin 28, Bois d’Asson 70, Dauphin 132, Dauphin 144, Dauphin 172, Bois d’Asson 176.

Localities. Bois d’Asson

Diagnosis. The species is quite similar to Plecia livida , but the rounded lobe at the base of the gonostylus in the male and the slight kink in Rs at the furcation with R2+ 3 in the female may be diagnostic for the species.

Redescription. Male: Total length 4.8 – 8.3 mm (N=7).

Head (fig. 150): Length 0.77 – 0.97 mm (N=3), width 1.01 mm (N=1). Dark brown, probably black in life. Antenna slender, flagellum 7- or 8-segmented. Rostrum slightly elongated, approximately half as long as compound eye. Ocellar triangle rather low, not very prominent. Palp robust.

Thorax: Length 1.5 – 2.4 mm (N=7), width 1.6 mm (N=1). Dark brown, probably black in life. Pile not conspicuous. Haltere pale.

Wing (fig. 149): Length 4.3 – 6.1 mm (N=7), width 1.6 – 2.4 mm (N=7), length/width = 2.42 – 2.79 (N=7). Light brownish, radial veins brown, more posterior veins concolourous with membrane. Subcosta distinctive, straight. R2+3 short and curved. Costa extends to nearly half-way between apices of R4+5 and M1. R4+5 apically moderately curved. Wing vein measurements in Table 3 .

Legs: Brown, slender but not particularly long. Tarsi slender. Metatibial spur dark brown, short, relatively strong. Length of fore femur 1.5 mm (N=1), fore tibia 1.3 – 1.8 mm (N=4), hind femur 1.6 – 2.2 mm (N=4), hind tibia 1.8 – 2.3 mm (N=6).

Abdomen: Length 3.1 – 5.9 mm (N=7). Brown, conical.

Terminalia (fig. 152): Hypopygium width 0.75 – 0.85 mm (N=4). Dark brown. Epandrium dome-shaped, apically with three short, knob-like points. Gonostylus 0.32 – 0.57 mm long (N=6), slender, digitiform, slightly curved, basally with a rounded, knob-like dorsal lobe.

Female: Total length 7.0 – 9.5 mm (N=9)

Head (fig. 151): Length 0.81 – 0.85 mm (N=2), width 0.75 – 1.04 mm (N=7). Dark brown, rounded, a little wider than long. Compound eye flat, about as long as temples. Antenna slender and pointed, flagellum 7- or 8-segmented.

Thorax: Length 1.9 – 2.9 mm (N=8), width 1.5 – 2.1 mm (N=6). Dark brown. Haltere light brown.

Wing: Length 5.9 – 8.1 mm (N=9), width 2.3 – 3.2 mm (N=9), length/width = 2.31 – 2.71 (N=9). Light brownish fumose, veins brown. Pterostigma light brown, rather indistinctive. Costa extends half-way between apices of R4+5 and M1. Rs with a little kink where R2+3 branches off. R2+3 moderately long, strongly curved basally. R4+5 moderately curved apically. Crossvein R-M vertical. Wing vein measurements in Table 3 .

Legs: Dark brown.

Abdomen: Length 4.5 – 7.2 mm (N=9), width 1.5 – 2.4 mm (N=8). Reddish brown, robust.

Terminalia (fig. 153): Cerci large and prominent, two-segmented.

Fig. 150. Male, habitus. RGL Dauphín 122.

Fig. 151. Female, habitus. RGL Bois d’Asson 4.

Fig. 152. Male, terminalia, dorsal. RGL Bois d’Asson 24. Fig. 153. Female, terminalia, dorsal. RGL Bois d’Asson 4.

The sexual size dimorphism of this species was commented upon by Gentilini (1993). Such a size difference is possible due to the large variability in size in bibionids, and it is probably as common a trait among fossil bibionids as it is among recent ones. Caution is warranted when trying to associate male and female specimens since females may be considerably larger than conspecific males. This trend is not universal, however, since in many recent species females are smaller than males at least with respect to body length.