Orthoceratium lacustre (Scopoli, 1763)

Pollet, Marc & Stark, Andreas, 2018, The quest for the identity of Orthoceratiumlacustre (Scopoli, 1763) reveals centuries of misidentifications (Diptera, Dolichopodidae), ZooKeys 782, pp. 49-79 : 49

Orthoceratium lacustre (Scopoli, 1763) Figs 1, 2, 3 A–B, 4A, B, D, F, 5 A–B, 6 A–B, 7, 10B

Musca lacustris Scopoli, 1763: 343. Type locality: Carniola (= present-day Slovenia) - presumably transferred to Orthoceratium by Schrank (1803)

Notes on synonyms.

Musca formosa Haliday, 1832 and Medeterus viridipes Macquart, 1834, previously listed as synonyms of O. lacustre , clearly refer to O. sabulosum (see further).

Diagnosis.

Large, short-bodied, slender, entirely green species with abdomen 1.6 × as long as thorax (Figs 2, 3A, B). All legs mainly dark and metallic with narrowly yellow knees. Wing smokey reddish yellow, with reddish yellow veins (Fig. 5A, B). Apical section of vein M1 with strong sinous bend at ½. Posterior border of wing indented at vein CuA1. Coxa I with strong white pubescence, and with three black bristles only at apex. Coxa II with only pale bristles at apex anteriorly. Pedicel with short apical bristles (Figure 4F). Ac uniseriate, rather small, at most 1/3 as long as dc. Male: face not as wide as postpedicel is long (Figure 4A). Postpedicel elongate triangular, at least 1.2 × as long as deep (Figure 4D). TV with blunt ventral process at each side bearing short dark separate bristles (Figure 10B). Femur I with small ovoid brownish yellow pv tuft just beyond basal 1/4, about 1/8 of femur length (Figure 6A). Femora I–II with multiple rows of very short white erect setae on basal ½. Tibia II with three ad bristles, with basal bristle shorter, and with one av bristle. Tibia III with four strong and one small pd bristles. Tarsus I with only one claw, and tarsomere taI1 mostly unmetallic (Figure 6B).

Redescription.

Male. Body length: 5.0-5.7 mm (n = 25); wing length: 5.2-6.2 mm (n = 44), 0.3 × as wide as long. Head (Fig. 4A, B, D, F). Face silvery white, slightly narrowing towards middle of face, then widening towards clypeus, latter with triangular lower margin, weakly projecting; face 0.9 × as wide as postpedicel (length), with short white pubescence. Frons with metallic green ground colour, strongly dusted yellowish white. Occiput with metallic green ground colour, dusted whitish, convex in middle. Palp 1/5-1/4 of eye, triangular, dark brown, strongly dusted whitish, with white pubescence, and apical bristle absent. Proboscis dark brown. Eyes red, with short white pubescence. Uppermost seven to nine postocular bristles erect, black, and lower bristles curved, white, forming whiskers. One pair of black postocellar bristles. Antenna entirely dark brown, with scape bare and pedicel with apical crown of short bristles; postpedicel dark brown, elongate triangular, with blunt apex, 1.2-1.4 × as long as deep, 0.9-1.3 × as long as scape and pedicel combined, with short pubescence; arista-like stylus dorsal, inserted at middle of upper rim of postpedicel, 2.0-2.4 × as long as first three antennal segments combined, bare. Thorax (Figs 2, 3A). Mesonotum entirely brilliant metallic green with sometimes bluish violet tinge, strongly dusted greyish white on pleura and certain zones on dorsum, only without dusting between dc and ac, and between dc and npl areas; scutellum bluish violet, bare on dorsum, with four marginal bristles, lateral pair much smaller than median pair. Anterior spiracle with group of multiple curved, yellowish white, long setae. Thoracic bristles black. Seven dc, with 1stdc laterally off-set, and 6-7thdc stronger; three to five ac, uniseriate, reaching level between 5th and 6thdc, rather small, at most 1/3 × as long as dc; with two strong black and one minute white ant pprn, one internal and one external bas pprn, one psut ial, one sut ial, two npl, two spal, and one pal bristles. Upper proepisternum with a large group of long yellowish white curved setae; lower proepisternum with one strong black curved bristle and a small group of yellowish white curved setae. Wing (Figure 5A). Smokey reddish yellow, with reddish yellow veins. Vein R4+5 sinuous near wing apex, there parallel with vein M1; apical section of vein M1 with strong sinous bend at ½ (MSSC); crossvein dm-cu rather straight; posterior border of wing indented at vein CuA1. Proximal section of vein M1 1.9 × as long as apical section. Proximal section of vein CuA1 8.5 × as long as apical section. CuAx ratio: 1.7. Halter pale, calypteral fringe yellowish white. Legs (Figs 2, 3A, 6 A–B). Overall dark, metallic green to violet, with pale yellow knees in all legs, and with black bristles. Coxae dark, with metallic green ground colour and strongly dusted whitish, coxae I–II with about apical 1/4 yellow, coxa III with about apical 1/3 yellow. Coxa I with dense, white pubescence and three rather small, black ap bristles. Coxa II with dense white pubescence on anterior face, and one black inclined bristle at 1/2 on margin; lateral face bare. Coxa III with one black, erect external bristle, inserted at 1/2, with vertical row of white setae. Trochanters dark brown. Femora I–III brilliant metallic green, sometimes with violet tinge, femora I–II with pale yellow knee on apical 1/8, and on apical 1/10 in femur III. Femur I with multiple rows of very short white erect setae on basal ½ (MSSC); with small ovoid brownish yellow pv tuft just beyond basal 1/4, about 1/8 of femur length (MSSC); with one rather small pv preapical bristle. Femur II with one strong ad preapical bristle, at less than apical 1/5, and with one small pv preapical bristle; with one row of very short white erect vt setae on basal 1/3 (MSSC), and with one row of short inclined pv setae along entire length, white on basal 2/3 and black on apical 1/3, longest at basis and apex. Femur III with one strong ad preapical bristle, at about apical 1/3, and one small pv preapical bristle; sometimes with some thin inclined (thus not erect!) ds bristles in basal 1/5. Tibiae I–III brilliant metallic green to violet, tibia I with basal 1/8, tibia II with basal 1/9, and tibia III with less than basal 1/10 pale yellow. Tibia I with two ds bristles, 2-3 × as long as tibia is deep; with two small ad bristles, 1-1.5 × as long as tibia is deep, and with two to three pv bristles, 2-3 × as long as tibia is deep; with white pilosity on av face along entire length, and with two small ap bristles. Tibia II with three ad bristles, about 3 × as long as tibia is deep, with basal bristle shorter; with two pd bristles, 2 × as long as tibia is deep, with basal bristle shorter, and with four ap bristles; with one av bristle at basal 2/3 and one pv bristle at basal 1/5, both 2 × as long as tibia is deep; and two small pv bristles in apical 1/2, not as long as tibia is deep. Tibia III with five ad bristles, about 2.5 × as long as tibia is deep, four strong and one small pd bristles, former about 2.5 x, latter not as long as tibia is deep, and four strong ap bristles; with distinct pd row on apical 1/2; with three-four av bristles, 1-1.5 × as long as tibia is deep, and with multiple shorter pv setae along entire length. Tarsi I–III dark brown, with taI1 mostly unmetallic and taII1 and taIII1 with metallic green to violet reflection. Tarsus I with taI1 with pale ventral pubescence (MSSC) with some darker short bristles; taI5 with long curved dorsal setae at apex, 0.7 × as long as taI5 length; only inner claw present (MSSC). Tarsus II with taII1 with multiple short vt bristles, nearly as long as taII1 is deep. Tarsus III with taIII1 with multiple inclined vt bristles, longest about as long as taIII1 is deep. Ratio of femur/tibia/tarsomeres 1-5 in leg I: 10.3/11.4/6.3/2.2/1.5/1/1.1, in leg II: 9.5/12.2/8.4/3.7/2.4/1.3/1, and in leg III: 10.6/15.3/6.7/4.6/2.8/1.4/1. Abdomen (Figure 2, 3A). Basal five segments pubescent, 6th bare, minute, only visible dorsally. T brilliant metallic green, with bluish or with bronze tinge in some specimens, strongly dusted whitish on lower margins, with short dense black pubescence on dorsum, long yellowish white setae laterally, strongest on sides of TI, and TI–IV with black bristles on posterior margin, strongest on TI; TV brilliant metallic green without prominent dark bristles on posterior margin, with blunt ventral process at each side, with short dark separate bristles (MSSC) (Figure 10B). ST with green ground colour, strongly dusted whitish, with yellowish white, erect bristles. Hypopygium (Figure 7) with epandrium concolorous with tergites; hypandrium rather stout with subcircular apex, with ventrally curled up sides forming a gutter; phallus slender and strongly curved; three basoventral epandrial setae of subequal size, and apicoventral epandrial lobe pale reddish yellow, stout, narrowing towards apex and adjacent to outer surstylar lobe; surstylus with robust pale reddish yellow outer (or dorsal) lobe with area of minute spines near apex and with subcircular bristle at apex, inner (or ventral) surstylar lobe dark, robust with tapering apex baring a few bristles; postgonites robust, dark, with apical pubescence and a vt process; cercus dark brown, medium-sized, rather rectangular, apex large subcircular, with dense yellow pubescence, dark brown. Female (Figure 3B). Body length: 5.4-6.2 mm (n = 23); wing length: 5.2-6.7 mm (n = 51), 0.3 × as wide as long. As male, except for: abdomen 1.4 × as long as thorax, slender. Face 1.7-2.3 × as wide as postpedicel (length). Frons ground colour metallic green, strongly dusted yellowish white. Palp ovoid. Uppermost eight to ten postocular bristles black. Antenna dark brown, with scape sometimes paler (yellowish brown); postpedicel triangular, with blunt apex, 0.9-1.1 × as long as deep, 0.8-0.9 × as long as scape and pedicel combined; arista-like stylus 2.4-2.7 × as long as first three antennal segments combined. Thorax with four to five ac, reaching between 4th or 5thdc. Wing (Figure 5B) with vein R4+5 bended but straight near wing apex, there parallel with vein M1; apical section of vein M1 with weak bend (sinuous) at 1/2; crossvein dm-cu straight. Proximal section of M 1.7 × as long as apical section. Proximal section of CuA1 6.9 × as long as apical section. CuAx ratio: 1.6. Coxa I with two to three rather small, black ap bristles. Femur I bare ventrally. Femur III often with some thin inclined ds bristles in basal 1/5. Tibiae I–II with basal 1/10 pale yellow; tibia I with three pv bristles. Tibia II with two av bristles at basal 2/5 and 2/3, 2-2.5 × as long as tibia is deep, and four small pv bristles on entirely length, not as long as tibia is deep. Tibia III with ad bristles about 3 × as long as tibia is deep, and with four strong pd bristles, 2.5-4 × as long as tibia is deep. Tibia III with av bristles 1.5-2.0 × as long as tibia is deep. Tarsus I with taI1 with multiple short black ventral bristles, nearly as long as taI1 is deep; taI5 with both claws. Ratio of femur/tibia/tarsomeres 1-5 in leg I: 8.6/9.5/5.7/2.3/1.5/1/1.1, in leg II: 9.1/11.6/8.1/3.4/2/1.2/1, and in leg III: 10.6/15/6.4/4.3/2.6/1.4/1. Abdomen with five pubescent segments, 6th invisible; also STIV with strong whitish dusting.

Type specimens.

ITALY: NEOTYPE (here designated to fix the identity of the species) ♂, [brownish rectangular] "Liancalus/ lacustris Scp"/ “Görz.” [= Gorizia, in Friuli-Venezia Giulia region]; "Zool. Mus."/ “Berlin”; "Orthoceratium lacustre"/ "(Scopoli, 1763)"/ "det. Marc Pollet, 2017"; [red rectangular] “NEOTYPE” / "des. Marc Pollet, 2018" (2017 on initial label in Figure 1) [ZMHB] (IT-04).

Other material examined.

See Suppl. material 1. List of (non-type) records of Orthoceratium .

Remarks.

In order to fix the identity of the species, a neotype of O. lacustre was selected on the basis of the locality (closest to the original type locality or region), and the preservation status of the specimen (see Figure 2).

Of all examined specimens (n = 131) one Trieste specimen featured a strong curved black bristle on the right fore coxa.

Distribution.

As a result of the taxonomic mix-up between both species in the past, previous distribution records of O. lacustre in the literature - many of which refer to O. sabulosum in reality - must be considered unreliable. Our present study revealed that O. lacustre has been collected nearly exclusively along the northern border of the Mediterranean basin (incl. adjacent islands), both in coastal habitats and inland (montane) habitats (see Figure 1). Its current distribution range includes: France (depts Hérault, Var, Bouches-du-Rhône, Gard), Italy (Sardinia, Gorizia, Livorno, Syracuse, Taranto, Veneto), Slovenia (see Scopoli 1763), Montenegro (Central Region), Croatia (Dubrovnik-Neretva Co.), Greece (Ionian and North Aegean Islands, Serres, Thessaloniki, Trikala), Bulgaria (Burgas), and Algeria (Oran). Its range overlaps with that of O. sabulosum only in Oran (Algeria), and on the islands of Sardinia (Italy) and Lesvos (Greece). In the latter site, both species have been collected (in different years by different collectors) in the same area.

Previous records from Austria, Ireland, Madeira or Crimea (Ukraine) could not be verified due to a lack of specimens, but it is very likely that the Irish and Madeiran records refer to O. sabulosum (see Figure 1).

Ecology.

With only two clear exceptions, O. lacustre has been recorded from mostly lowland locations in a 25 km zone along the Mediterranean coast, where it seems to occur along inland lakes which also corresponds with the description of the habitat of the type specimens ( Scopoli 1763). Only on Sardinia (at 480m) and in Greece (prov. Serres) has the species been collected in habitats less or not affected by the sea. At the two Greek sites, both above 1,100m, and presumably also in Sardinia, the species occurred along small streams in mixed forest (beech and spruce forest in Greece).