Drymeia fratercula, Pont, 2022

Pont, Adrian C., 2022, The genus Drymeia Meigen in the Caucasus Mountains, with a note on the identity of Aspilia glacialis Rondani, 1866 (Diptera: Muscidae), Zootaxa 5134 (3), pp. 355-382 : 364-368

Drymeia fratercula sp. nov.

Figs 10–18

Diagnosis. This species is close to the Alpine Drymeia glacialis ( Rondani, 1866) , e.g. 3 postsutural dorsocentrals, very broad parafacial, and conspicuous facial snout. However, D. glacialis is a larger, more robust species with longer and stronger setae, and the male has the frontal width equal to diameter of anterior ocellus; hind femur with no or few posteroventrals in apical half; fore tarsus with tarsomere 1 produced posteroventrally at tip into a conspicuous thorn, and tarsomere 1 almost as long as the length of tarsomeres 2–5 combined.

Etymology. The specific name “ fratercula ” is Latin and means “little brother”. This reflects the close similarity between this species and D. glacialis (Rondani) .

Type-material Examined. Holotype ♂. GEORGIA: Mtskheta-Mtianeti region: Mt Koltesh [~ 42°37’N 44°45’E], meadow/heath, 2300 m, 8.vii.1983, A.C. Pont ( BMNH) . Paratypes 11♂ 11♀. GEORGIA: Mtskheta-Mtianeti (Kazbegi district): data as for holotype , 4♂ 3♀ (2♂ OUMNH & ZMUM, rest BMNH); same data but date, 30.vi.1983 , 3♂ 2♀ (1♂ 1♀ SZNM, rest BMNH); Mt Koltesh , heath, 2500 m, 30.vi.1983 (A.C. Pont) , 2♀ ( OUMNH & BMNH); Gergeti [~ 42°42’N 44°31’E], upper heaths, 2300–3000 m, 11.vi.1983 (A.C. Pont) , 3♀ (1 ZMUM, 2 BMNH). ARMENIA: Aragatsotn: Mt Aragats , 40°29’N 44°11’E 3380–3420 m, 21.vii.2015 (A.C. Pont) , 1♂ ( OUMNH); Lake Kari , 40°28’N 44°11’E, 3190 m, 21.vii.2015 (A.C. Pont) , 1♀ ( OUMNH). RUSSIA: Caucasus Reserve, Lagonaki Plateau , 11–12.vii.2008 (O. Kosterin) , 3♂ ( ZMUM) .

Description. ♂.

Head ( Fig. 12 ). Ground-colour black. Eye bare. Fronto-orbital plate silvery-white pruinose below, dull above; parafacial silvery-white pruinose; face grey, and gena light grey pruinose; most of occiput subshining. Frons at narrowest point separated by a distance equal to 2–3 times diameter of anterior ocellus, the margins of each fronto-orbital plate touching or narrowly separated on upper half of frons where the frontal vitta may be obsolete. Ocellar setae long. 12 pairs of frontal setae, including interstitials, and above them, just in front of ocellar tubercle, with 2 pairs of short, fine, reclinate orbitals.Antenna black, postpedicel twice as long as wide. Arista short-pubescent, the individual hairs shorter than its basal diameter. Parafacial at level of insertion of arista twice width of postpedicel, narrowing sharply below. Upper part of face with a conspicuous knob separating antennal bases. In lateral view, facial edge in front of level of profrons. Gena broad, depth below lowest eye-margin equal to length of postpedicel, densely setose and with a group of upcurved setae on anterior part of genal dilation. Occipital setulae long and dense. Palpus black, slender. Proboscis very long, slender, prementum dusted.

Thorax. Ground-colour black. Scutum matt, black, with very indistinct grey vittae before suture, running inside the line of the dorsocentrals, and brownish-grey vittae running between the intra-alar and dorsocentral rows before and after suture ( Fig. 11 ). Ground-setulae fine, erect. Postpronotal lobe light grey dusted. Pleura thinly dusted. Acrostichals 0+1, the presutural setulae in 3–4 irregular rows. Dorsocentrals 2+3, exceptionally 2+4. Prealar strong, much longer than 2nd notopleural. Notopleuron densely setulose. Prosternum bare. Katepisternal setae 1+2, with 2–3 stronger setulae below posterior seta, anterior seta fine. Scutellum black and undusted in posterior view; bare laterally and ventrally.

Legs. Black. Fore tibia with 3 posteroventral setae and 2–3 stronger anterodorsal setulae just before apex; apical posteroventral seta at most 2/3 as long as length of fore tarsomere 1. Fore tarsomere 1 not as long as the length of tarsomeres 2–5 combined, not modified, with the posteroventral apical thorn very inconspicuous. Fore claws very short, half as long as length of tarsomere 5, blunt-tipped. Mid femur weakly curved; with complete rows of anteroventral and posteroventral setae, all longer than femoral depth, the posteroventrals rather shorter than the anteroventrals; 0 anterior and 2 posterodorsal to posterior preapical setae. Mid tibia with 3 strong and 2 short anterodorsals, 3 strong and 2 short posterodorsals, 4–5 short anteroventrals, and 4 posteroventrals. Mid tarsomere 1 with the ventral spinules shorter than tarsal depth. Hind femur with complete rows of long strong anteroventral and posteroventral setae, all much longer than femoral depth. Hind tibia with 4–5 posterodorsals, 3–4 strong anterodorsals interspersed with 4–5 shorter setae, 4–5 anteroventrals, and 4–5 fine posteroventrals; 1 dorsal and 1 short anterodorsal preapical seta; ventral tip slightly produced, with 1 anteroventral and 1 posteroventral apical seta ( Fig. 13 ). Hind tarsomere 1 with a short ventral seta at base.

Wing. Brown, especially at base ( Fig. 10 ). Basicosta and tegula black. Costa with weak spinules, without costal spine. Cross-vein r-m distinctly beyond the point where subcosta enters costa. Cross-vein dm-cu oblique, almost straight. Calypters creamy, margins deeper yellow. Knob of haltere black.

Abdomen. Ground-colour black. When viewed from above, appearing matt with grey dust at sides of syntergite 1+2 and forming broad antero-lateral patches on tergites 3–5. Setae strong and erect laterally and medially on all tergites, except medially on syntergite 1+2. Sternite 1 bare. Sternite 5 ( Fig. 15 ).

Terminalia ( Figs 17–18 ). Syntergite 6+7+8 with long dense setae.

Measurements. Length of body, 6.0 mm. Length of wing, 4.5 mm.

♀. Differs from the male as follows:

Head. Dichoptic. Frons at middle 0.4 of head-width at this point, and here each fronto-orbital plate 0.3 of frontal vitta. Frontal triangle inconspicuous, not reaching the crossed setae on frontal vitta. 6–7 pairs of inclinate frontal setae, including several interstitials; 3 pairs of orbital setae, the upper two pairs reclinate and exclinate, the lower pair proclinate and exclinate. Frontal vitta with a pair of strong crossed setae. Fronto-orbital plate bare apart from the setae. Occipital setae shorter and less dense.

Legs. Fore tarsomeres 1–4 ( Fig. 14 ) with dense fine erect hairs on ventral surfaces, mostly as long as tarsal depth. Mid femur straight. Hind tibia with 4–5 anterodorsals and 4–5 anteroventrals; without posteroventrals.

Wing. Brownish, especially at base. Costa with strong spinules from humeral cross-vein almost to tip of vein R1. Calypters yellow, their margins bright yellow.

Abdomen. Grey dusting more extensive, tergites 3–5 each with a poorly defined black median vitta, very broad on tergite 3, to narrow on tergite 5. Without strong setae.

Ovipositor. Long and slender, 1.7 times as long as length of abdomen. As in D. setibasis except that the two elongated rods of tergite 8 are fused into a single plate ( Fig. 16 ), and the two lines of setulae at the tip of the tergite are placed on a single weak plate.

Measurements. Length of body, 7.0 mm. Length of wing, 5.5 mm.

Remarks. In Sorokina & Pont (2015), D. fratercula keys out to D. glacialis (as D. alpicola Rondani ) from the European Alps from which it differs as stated in the diagnosis. The two species are extremely similar and are evidently sister-species. In the key by Fan (2008) it runs to couplet 29 but differs from the species therein by the armature of the ♂ mid femur. In the key by Xue et al. (2008) it runs to couplet 39 and to D. melargentea Fan from China (Yunnan).

Drymeia fratercula and D. glacialis can be separated by the following key couplet:

- Larger and more robust species, length up to 8 mm, with strong setae. Fore tibia with the apical posteroventral seta long, almost as long as fore tarsomere 1. ♂: fore tarsomere 1 with a distinct posteroventral apical thorn; frons at narrowest point usually equal in width to diameter of anterior ocellus; hind femur with no or few posteroventral setae in apical half. ♀: the mat of ventral hairs on fore tarsomeres 2–4 much longer than the depth of the tarsomeres............................. D. glacialis (Rondani)

- Smaller and less robust species, length up to 7 mm, with weaker setae. Fore tibia with the apical posteroventral seta a little over half as long as length of fore tarsomere 1. ♂: fore tarsomere 1 with the posteroventral apical thorn very inconspicuous; frons at narrowest point separated by a distance equal to 2–3 times diameter of anterior ocellus; hind femur with a complete row of posteroventral setae. ♀: the mat of ventral hairs on fore tarsomeres 2–4 not as long as the depth of the tarsomeres D. fratercula sp. nov.

Some of these differential characters are slightly variable, but these two allopatric taxa appear to be species in the process of divergence. D. glacialis is found in the Western Palaearctic only in the European Alps, where it occupies the highest alpine biotopes, meadows and alpine heaths from 1450 to 2500 m. D. fratercula is endemic to the Caucasus Mountains and is found only in the zone of alpine heaths from 2300 to 3420 m asl. The Alps and the Caucasus are two segments of the late Coenozoic trans-Eurasian orogenic belt ( Sharkov et al. 2015). During the Quaternary glaciations the snow-line in the Caucasus was up to 1300 m lower than it is at present ( Tielidze 2017, Revaz et al. 2018) and the foothills were in the tundra zone. During subsequent warming, the retreating tundra led to the faunistic isolation of these two ranges and the tundra fauna eventually occupied the highest zones where individual taxa have evidently begun to separate into sister-species.

Note on Aspilia glacialis Rondani, 1866 . This species was described by Rondani from a single female from the Insubrian Alps of northern Italy (“unicum exemplar collectionis meae ... in Alpibus Insubriae captum et olim a Clar. De Cristofari Mediolanensi missum”). The name was tentatively synonymised with Drymeia alpicola (Rondani, 1870) (as Pogonomyia ) by Stein (in Becker et al. 1907: 631). In the course of his revision of the Palaearctic Muscidae, Hennig (1961) studied Rondani’s collection but did not find the holotype. Later ( Hennig, 1962b), after correspondence with several Italian Museums, he reported that the holotype must be presumed lost and D. glacialis remained as an “unrecognised species” although the possibility of a synonymy with D. alpicola was left open ( Hennig 1962b: 677; Pont 1986: 73).

The holotype has recently been located in MZUF ( Sforzi & Sommaggio 2021: 140). It is a female, with two labels: (1) A white oval label, with “1162” printed in red ink; (2) A red label with the printed information “Museu “La Specola” / coll. Rondani / HOLOTYPUS ”. It is in fair condition ( Fig. 19 ): slightly mouldy and dusty; both postpedicels and right hind leg missing; ptilinum partly extruded; right wing with part of costa missing; beetle damage to left side of syntergite 1+2; many setae on scutum rubbed off. Nevertheless, it can be recognised as Drymeia alpicola ( Rondani, 1871) on account of the very enlarged parafacial, elongate proboscis, presence of a small snout between the antennal bases, and dense fine ventral setulae on fore tarsomeres 1–4, and, being an earlier name, must replace D. alpicola . This information was passed to Drs Jade Savage (Sherbrooke, Canada) and Vera Sorokina (Novosibirsk, Russia) who formally published the synonymy ( Savage & Sorokina 2021: 51).

Figures

FIGURE 19. Drymeia glacialis (Rondani), ♀ holotype, lateral view.

FIGURES 10–11. Drymeia fratercula sp. nov., ♂ habitus. 10. Lateral view. 11. Dorsal view. (holotype; Georgia, Kazbegi, Mt Koltesh, meadow/heath, 2300 m, 8.vii.1983.)

FIGURES 12–16. Drymeia fratercula sp.nov. 12. ♂ head, lateral view. 13. ♂ hind tibia and tarsomere 1, posterior view. 14. ♀ fore tarsomeres, anterior view. 15. ♂ sternite 5, dorsal view. 16. ♀ tergite 8. Scale-line 0.25 mm (15), 0.5 mm (16). (Georgia, Ka- zbegi, Mt Koltesh, meadow/heath, 2300 m, 8.vii.1983 (12, 13) and 30.vi.1983 (14, 16); Mt Koltesh, heath, 2500 m, 30.vi.1983 (15).)

FIGURES 17–18. Drymeia fratercula sp.nov., ♂ terminalia. 17. Cercal plate, dorsal view. 18. Hypopygium, lateral view. Scale lines 0.25 mm. (Georgia, Kazbegi, Mt Koltesh, heath, 2500 m, 30.vi.1983.)