Dicranomyia (Dicranomyia) imbecilla Lackschewitz

Starý, Jaroslav & Stubbs, Alan E., 2015, Five species under Dicranomyia (Dicranomyia) mitis (Meigen, 1830) (Diptera, Limoniidae), Zootaxa 3964 (3), pp. 321-334 : 332-333

Dicranomyia (Dicranomyia) imbecilla Lackschewitz in Lackschewitz & Pagast, 1941, stat. n.

Figs 5 , 10 , 15 , 20

Dicranomyia (Dicranomyia) mitis var. imbecilla: Lackschewitz in Lackschewitz & Pagast 1941: 30 (description), Plate 7, Fig. 56 (male terminalia).

Species B: Stubbs 1998a: 23 (key), Figs (male tarsus, male terminalia).

Diagnosis. Small species. Body colouration ochreous to yellowish-brown, very pallid in life. Wing clear, with only sometimes feebly indicated pterostigma. Sc1 without any macrotrichia. Male tarsomere 5 distinctly shorter than tarsomere 4; male tarsal claws with single well-developed tooth at base. Male terminalia with rostral prolongation of ventral gonostylus truncate close beyond medial spine; rostral spines almost straight, separated at base by more than their own breadth. Female terminalia with cercus subequal in length to tergite 10; space between cerci subequal in width to cercus breadth at base. Wing length 5.3–7.6 mm.

Redescription. Male. Head with light grey pruinosity on frons and vertex, rostrum brown. Antenna brown to dark brown, reaching to about anterior margin of prescutum. Flagellomeres short-ovoid, gradually narrowed towards apex of antenna, with verticils distinctly shorter than respective segments. Palpus dark brown.

Thorax generally ochreous to yellowish-brown, sometimes rather dark dorsally. Pronotum ochreous to dark brown. Prescutum yellowish-brown, with thin pale grey pruinosity, darker medially as well as on scutal lobes; scutellum yellowed anteriorly, mediotergite usually dark brown. Pleuron ochreous, generally paler than dorsum of thorax. Wing clear, practically without any pattern, with at most vaguely indicated pterostigma (Fig. 20). Sc1 without any macrotrichia. Halter with knob infuscated. Legs practically yellow throughout, with only distal tarsomeres slightly infuscated. Two last tarsomeres short, quite different from those of other species treated here. Tarsomere 5 distinctly shorter than tarsomere 4, somewhat flattened, with sinuous ventral margin and, ventrally, with pair of long unusually stout setae at about two fifths of its length and a few similarly long but fine setae at base. Tarsal claws moderately long, about half length of tarsomere 5, with single well-developed tooth at base ( Fig. 5 ).

Abdomen brown dorsally, paler ventrally. Male terminalia ( Fig. 10 ): Tergite 9 rather long, about twice as broad as long, with shallow, rather U-shaped, median emargination at posterior margin and incomplete median suture. Gonocoxite moderately long, about half length of ventral gonostylus. The latter long-ovoid, about twice as long as broad. Rostral prolongation of ventral gonostylus truncate close beyond medial spine. Rostral spines almost straight, separated at base by more than their own breadth.

Female. Resembling male in general appearance, except that tarsal claws are quite different, much as in females (and also males) of other species treated here. Female terminalia ( Fig. 15 ): Cercus gently upturned, subequal in length to tergite 10. Space between cerci subequal in width to cercus breadth at base. Genital fork (vaginal apodeme) triangular, extending beyond posterior margin of tergite 10. Sternum 9 long, more than half length of tergite 10.

Material examined (85 ♂, 16 ♀). Bulgaria: Varna, Pobiti kamni, 28. v.1968, 1 ♂ (J. Starý leg., JSO). Czech Republic: Hrubý Jeseník Mts, Branná, Klepáčský brook (700 m), 9. vii.2002, 1 ♂, “Dembauda” (900 m), 21. vii.1999, 1 ♂ (at light), 10. viii.1999, 1 ♂; Horní Údolí nr. Zlaté Hory, 14. viii.1992, 1 ♂, Příčný vrch [hill] (850 m), 11. viii.1992, 1 ♀; Hrubý Jeseník Mts, Kouty nad Desnou, Divoká Desná valley, “Zámčisko” (970 m), 21. vii.2003, 6 ♂, 30. viii.2005, 8 ♂, 2 ♀, 26. viii.2008, 1 ♂, 20. viii.2009, 4 ♂, 1 ♀ (all at light); Hrubý Jeseník Mts, Praděd, Bílá Opava valley (1200–1250 m), 23. ix.1971, 1 ♂, 15. ix.1976, 1 ♂, 7. x.1997, 3 ♂, 17. viii.1998, 3 ♂ (at light), 27. viii.2002, 2 ♂, 1 ♀ (at light); Hrubý Jeseník Mts, Velká kotlina (over 2000 m), 26. viii.1987, 1 ♂; Hrubý Jeseník Mts, Karlova Studánka (900 m), 5. xi.1993, 2 ♂, 26. viii.1998, 2 ♂; Libavá env., Údolná, Odra valley, 21. vii.1995, 1 ♂; Javoříčko, Špranek valley, 8. vii.1987, 3 ♂, 1 ♀, 10. viii.1995, 1 ♂; Štramberk, Kotouč—quarry, “Mokřadlo”, 10. vii.2001, 1 ♂, 15. viii.2001, 1 ♂ (at light), 30. vi.2003, 1 ♂ (at light), 27. vii.2005, 7 ♂ (at light); Moravskoslezské Beskydy Mts, Tanečnice (900–1000 m), 11. ix.1984, 1 ♂; Moravskoslezské Beskydy Mts, “Malinová” (700–800 m), 19. vii.1990, 1 ♂; Moravskoslezské Beskydy Mts, Prostřední Bečva (600 m), 30. vii.1992, 1 ♂, 19. viii.1992, 1 ♀; Hostýnské vrchy [hills], “Valaška” (500–600 m), 23. vii.1992, 2 ♂; Bílé Karpaty Mts, Javorník, “Machová”, 1. vii.1993, 1 ♂ (all J. Starý leg., all JSO). Great Britain: England: Yorkshire, Hayburn Wyke, 18. vii.1996, 1 ♂; Yorkshire, Kilnsey, 13. vii.1995, 3 ♂, 1 ♀ (all A.E. Stubbs, all ASP); Derbyshire, Dovedale, 25. vi.1911, 1 ♂ (F.W. Edwards leg., BMNH); Northumberland, Billamoor, 1. viii.1976, 1 ♂ (A.E. Stubbs leg., ASP). Scotland: Berwickshire, Coldingham Bay, 12. vii.1988, 1 ♂, 2 ♀ (A.E. Stubbs leg., ASP). Wales: Cwm Clyddach (South Wales), 25. viii.1972, 2 ♂, 1 ♀ (A.E. Stubbs leg., BMNH). Slovakia: Veľká Fatra Mts, Lubochnianska valley, 15. ix.1985, 1 ♂; Vysoké Tatry Mts, Mlynická valley, 27. viii.1972, 1 ♂; Vysoké Tatry Mts, Mengusovská valley (1200–1250 m), 12. viii.2003, 1 ♂; Vysoké Tatry Mts, Velické pleso (1665 m), 12. viii.2003, 1 ♂; Belianske Tatry Mts, Tristárska valley (1100 m), 5. ix.1977, 3 ♂, 5 ♀; Ždiar, Magura hotel, (900 m), 3. viii.1999, 1 ♂ (at light); Slovenský kras, Zádielska valley, 8. vii.1970, 1 ♂ (all J. Starý leg, all JSO). Switzerland: Canton Neuchâtel: Le Cachot, peat-bog, 6. ix.1995, 1 ♂; Chambrelien, 1. ix.1995, 1 ♂ (all J. Starý leg., all JSO). Canton Vaud: Bex, Pont de Nant (1250 m), 31. viii.1994, 1 ♂ (J. Starý leg., JSO). Canton Fribourg: Schwarzsee, 11. ix.1995, 4 ♂ (J. Starý leg., JSO).

Discussion. D. (D.) imbecilla is clearly separated from the other species treated here based on the structure of the male tarsal claws ( Fig. 5 ). This and other distinctions from D. (D.) lutea are specified in Discussion of the latter.

Ecology. In Great Britain, this is a rare species of western and northern districts, currently only known from northern England and south-west Scotland. Most localities have calcareous seepages depositing tufaceous substrate. The species can occur along spring-fed streams associated with seepage complexes, and, in one site, it was abundant beside a large woodland stream well below the source. June–July. ( AS). It should be noted that, in the Czech Republic and Slovakia, all the species (except for affinis which has not been recorded there) seem to prefer mountainous areas, but none is strictly confined to the mountains. D. (D.) imbecilla appears to be most prone to occur there, exceeding altitude 1600 m in the Vysoké Tatry Mts ( Slovakia). At the locality Prostřední Bečva ( Czech Republic: Moravskoslezské Beskydy Mts), it was collected together with D. (D.) mitis , D. (D.) quadra , and D. (D.) lutea , with two latter species on the same date (30.vii.1992) (JS).

Distribution. The species is here recorded for Bulgaria, Czech Republic, Great Britain, Slovakia, and Switzerland; another country record is Germany (type locality of imbecilla , see Lackschewitz & Pagast 1941). Probably more widely distributed in Europe.

Figures

FIGURES 1 – 5. T wo distal tarsomeres and tarsal claw (with details of tarsal claw). 1 — D. (D.) mitis (Czech Republic: Bohemia: Šumava Mts). 2 — D. (D.) affinis (Morocco: Rif Mts). 3 — D. (D.) quadra (Czech Republic: Moravia: Hrubý Jeseník Mts). 4 — D. (D.) lutea (Czech Republic: Moravia: Moravskoslezské Beskydy Mts). 5 — D. (D.) imbecilla (Czech Republic: Moravia: Hrubý Jeseník Mts). Scale bar 0.25 mm.

FIGURES 6 – 10. Male terminalia, general view, dorsal (with details of rostral prologation of ventral gonostylus). 6 — D. (D.) mitis (Czech Republic: Bohemia: Šumava Mts). 7 — D. (D.) affinis (Morocco: Rif Mts). 8 — D. (D.) quadra (Czech Republic: Moravia: Hrubý Jeseník Mts). 9 — D. (D.) lutea (Czech Republic: Moravia: Moravskoslezské Beskydy Mts). 10 — D. (D.) imbecilla (Czech Republic: Moravia: Hrubý Jeseník Mts). Scale bar 0.5 mm.

FIGURES 11 – 15. Female terminalia, internal structures, ventral. 11 — D. (D.) mitis (Czech Republic: Moravia: Moravskoslezské Beskydy Mts). 12 — D. (D.) affinis (Morocco: Rif Mts). 13 — D. (D.) quadra (Czech Republic: Moravia: Hrubý Jeseník Mts). 14 — D. (D.) lutea (Czech Republic: Moravia: Moravskoslezské Beskydy Mts). 15 — D. (D.) imbecilla (Czech Republic: Moravia: Hrubý Jeseník Mts). Scale bar 0.5 mm. ce—cerci; gf—genital fork (vaginal apodeme); ifp—infraanal plate; s 9 — sternum 9; t 10 — tergite 10.