Tachina viridis Fallen , 1810: 276.

Pohjoismaeki, Jaakko & Bergstroem, Christer, 2021, Review of the Nordic Gymnocheta Robineau-Desvoidy (Diptera, Tachinidae) with report of two species new to Europe, ZooKeys 1053, pp. 145-184 : 145

Tachina viridis Fallen, 1810: 276.

Notes.

The identity of Tachina viridis Fallén, 1810: 276. Gymnocheta viridis ( Fallén, 1810) is the oldest described Gymnocheta and represents the type species of the genus. The Fallén collection, drawer 13 (4), contains a single type specimen (formally the holotype) (Fig. 1B-E ) mounted on an old thick pin and is in good condition except for the missing antennae and broken vibrissae. There are also some missing frontal setae and median discal setae on tergites 3 and 4. The protruding lower facial margin (Fig. 1C ), metallic green femora (Fig. 1C ), indistinct costal spines (Fig. 1D ) and the shape of sternite 5 (Fig. 1E ) make it obvious that the specimen represents the species until now known as Gymnocheta magna Zimin, 1958. When Fallén (1820: 25) wrote "Linea vertices subferruginea, utrinque viridi nitens. Femora virida; tibiae tarsique nigra." [Frontal stripe brownish, both sides lustrous green. Femora green; tibiae and tarsi black.], he surely must have been looking at this specimen, as the femora of the represented species are notably green compared to the other European Gymnocheta . It is also obvious that the name Gymnocheta viridis used by Fallén, Zetterstedt, Wahlberg, and many subsequent authors until the work of Zimin has concealed at least two different species as shown by the examination of old Swedish specimens (see below).

As a further confirmation of the type specimen identity, the original description in Swedish also refers to a single male: "♂ Denna lysande art, funnen på kummin midsommartiden i Maltesholms trädgård i Skåne, …”. [This brilliant species, found on caraway [ Carum carvi ] in midsummer time in Maltesholms garden in Skåne, ….] ( Fallén 1810: 276). In later work Fallén (1820: 25) notes records by Zetterstedt while referring to his own previous work: "Mas et Fem. In paludosis Abusa, mense Majo, utrumque sexum legit Zetterstedt. In floribus Cari Carvi in horto praedii Maltesholm mense Junio, unicum marem Muscae caesaris magnitudine vidimus ipsi." [Males and Females. Zetterstedt collected both sexes in May [from] mires/bogs in Abusa [a place in Skåne]. In June on flowers of caraway in Maltesholm garden, a unique male observed, size of Musca [= Lucilia ] caesar]. Zetterstedt (1844: 1190) himself writes later about Tachina viridis : "Hab. in foliis fruticum & herbarum, etiam in floribus umbellatarum, locis paludosis mihi praesertim obbvia, per hortos & prata Sueciæ, 30 Maj.-15 Jun., minus frequens; scilicet in Scania ad Lund, Abusa, Maltesholm &c., passim; in templo Upsaliæ antiquæ semel a D. Prof Wahlberg capta; e Dania a D Stæger missa". [On foliage of shrubs and herbs as well as flowers of Apiaceae , on bogs/mires [and] I especially [have observed] in gardens and meadows in Sweden. May 30-June 15, less abundant; namely from Skåne to Lund, Abusa, Maltesholm etc., infrequent; in the old Uppsala collection of D. Prof. Wahlberg; many from Denmark by D. Staeger].

Two of these aforementioned non-type specimens are in the NHRS main collection:

1♀: Labels: Hlm / P.Wg. This is apparently the specimen mentioned by Zetterstedt (1844: 1190) "in templo Upsaliae antiquae semel a D. Prof. Wahlberg capta". This specimen, like that of the holotype, represents Gymnocheta magna Zimin; 1♂: Labels: Sc. // Z (on a small white tag). In contrast to the previous, this specimen represents the current concept of Gymnocheta viridis .

Three additional non-type specimens are present in the Diptera Scandinaviae Collection, drawer 22 in ZMLU: 1♂: Labels: lemon yellow tag // T. viridis / ♂. Abusa (handwritten by Zetterstedt). Identity: Gymnocheta viridis . This specimen is apparently one of those mentioned by Fallén (1820: 25) and by Zetterstedt (1844: 1190); 1♂: Labels: 9. // Staeger. Identity: Gymnocheta viridis . Zetterstedt 1844: 1190 mentioned this specimen; 1♀: Label: purple red tag // T. viridis / ♀. Lund. (handwritten by Zetterstedt). Identity: Gymnocheta magna (= Gymnocheta viridis sensu Fallén). This specimen is apparently the one from Lund mentioned by Zetterstedt (1844: 1190).

For the sake of nomenclatural stability, we propose maintaining the current usage of the names G. viridis and G. magna . Neotype specimen for Gymnocheta viridis will be assigned later if ICZN accepts the petition for the replacement of the holotype. The following redescription represents G. viridis in its prevailing concept.

Diagnosis.

A common, vivid metallic green Gymnocheta with strong costal spines and narrow frons in male.

Redescription.

Body length: 7.2-10.8 mm (n = 19).

Male (Figs 1A , 2C , 4C , Eiii, 5A:iii, B:iii, C:iii).

Colouration: Head covered with a greyish white microtomentum. The metallic ground colour subshiny at least partly on the genal dilation but the intensity of the shine depends on the direction of the incident light. Facial plate brown, in lower part sometimes with an indistinct metallic green tint. Occiput, postgena, genal dilation, ocellar tubercle metallic green in ground colour, frontal plate narrowly metallic green along the frontal setae. Palpus, clypeus (sometimes with a metallic green tint) and prementum dark brown to black, labella brown beige. Thorax and abdomen bright metallic green in ground colour, in varying degrees depending on the direction of the incident light with an indistinct light grey microtomentum. Scutum when viewed from the side and slightly from behind with four longitudinal stripes changing from grey to gilt or purple depending on the direction of the incident light. Proepisternum normally black, and densely covered with microtomentum, in larger specimens partly with a metallic green tint. Fore coxa in anterior region and femur posteriorly often with weak metallic green shine. Wing membrane around crossvein r-m not infuscated. Tegula and basicosta dark brown or black.

Head (Fig. 2C ): Frons intermediate in width between G. magna and G. lucida at its narrowest point 0.35-0.45 [0.40] (n = 20) × as wide as an eye in dorsal view. Frontal vitta gradually tapering toward ocellar tubercle. Head in lateral view somewhat protruding, width at level of antennal insertion 0.60-0.77 [0.71] × (n = 14) the horizontal eye diameter. Fronto-orbital plate with a row of 10-14 [11] medioclinate moderately strong frontal setae, and some additional setulae; three or four [three to the left four to the right] of them extending to the middle of the pedicel with the row curving laterally, uppermost tiny setula sometimes reclinate; fronto-orbital plate outside the frontal row of setae with sparsely spread short and tiny setulae. Height of face 0.76-0.88 [0.85] × the length of frons (n = 13). Gena in profile at narrowest point, 030-0.42 [0.40] (n = 14) × as high as vertical eye diameter. Lower facial margin normally slightly protruded; in strict lateral view normally not visible in front of vibrissa. Facial ridge on lower 0.2-0.25 of its length with 2-3 [3] strong and 0-2 [2] additional thinner supravibrissal setae, length of which at least subequal to narrowest width of parafacial, and 2-5 [5] thin and short setulae. Below the vibrissa 4-7 [5] strong subvibrissal setae continuous to the row of genal setae, the posteriormost subvibrissal seta close to the foremost lower genal margin. Inner vertical setae crossed, thin and normally just slightly longer than the ocellar setae, outer vertical setae poorly developed, subequal with or even shorter than the adjacent postocular setae. Postocular setae long and thin, apically pronouncedly bending forward over the eyes. Occiput with a pair of postocellar setae subequal with the ocellar setae. Occiput and postgena with white to greyish white hairs. Antennae: First flagellomere subrectangular, short and evenly curved posteriorly at apex, maximal width in lateral view 0.76-0.91 [0.87] (n = 15) × the actual width of parafacial, at narrowest point; 1.47-1.73 [1.56] (n = 14) × as long as pedicel. Arista widened in proximal 2/5, rarely ½, and gradually tapering towards apex.

Thorax: Prosternum bare. Scutum with 3(2)+3 [3+3] acrostichal, three or four dorsocentral and 1+3 intra-alar setae. Scutellum with 4(5) pairs of strong almost horizontal setae along margin, apical and subapical pairs slightly diverging; 2-4 [2] suberect discal setae, forming a row in front of the marginal setae, the strongest subequal to the lateral setae, rarely with an additional pair of strong median discal setae; tiny dorsal setulae numerous, the longest measuring 1/2 the length of the strongest dorsal seta.

Legs: Claws and pulvilli on fore legs subequal in length with fifth tarsal segment, the latter 1.8-2.0 (n = 6) × as long as tarsal segment 4. Fore tibia with a row of 5-8 [five and six] anterodorsal setae, and an irregular row of 4-8 [6] posterior setae. Preapical anterodorsal seta subequal with the preapical dorsal and preapical posterior setae; preapical posterodorsal seta short, its length rarely exceeding 1/3 of the dorsal seta. Mid tibia with 4-6 [4] anterodorsal setae, the strongest in the middle of row, 5-8 [7] posterior setae, one ventral seta often accompanied by an additional tiny setula. Hind tibia with a continuous row of 9-12 unequally strong anterodorsal setae / setulae, of which 4-6 represent strong setae, four or five posterodorsal setae and three (rarely four) anteroventral setae.

Wing: Usually two costal spines, the lower (ventral) spine strongest and ca. 2-3 × as long as the surrounding costal setulae, normally somewhat shorter than crossvein r-m. CS4 + CS5 2.1-2.4 (n = 12) × as long CS6. Vein R4+5 at base with 3-6 [three and four] ventral and 3-8 [4] dorsal setulae.

Abdomen (Fig. 4B ): Tergite 2 with 3(2) lateral setae on each side. Tergite 3 with (2)3-4 [2 pairs and one unpaired] unequally strong and often irregularly set pairs of median discal setae; a pair of median marginal setae and 3(2) [3] lateral setae on each side. Tergites 4 with 2-3(4) [2] pairs of unequally strong and likewise irregularly set median discal setae; in dorsal view with a full row of 10-14 [10] marginal setae; tergite 5 with two or three irregular rows of strong and medium strong discal setae and a dense row of weak marginal setae.

Terminalia (five dissections) (Figs 4B , Eiii, 5A:iii, B:iii, C:iii): Sternite 5 (Fig. 4B , Eiii) in ventral view with long and wide lobes; length of medial cleft ca. twice its maximal width. Lobes with widespread setulae, slightly curved inwards at apex. Dorsomedial process black and prominent, expanding backwards partly separated from the lobes. Basal plate bare, ca. 0.4 × as long as sternite 5 and 2.6-2.7 × as wide as long. Syncercus in lateral view (Fig. 5A :iii) smoothly curved at apex, in dorsal view (Fig. 5B :iii) triangular, with long basal lobes and rounded apex; 1.6-1.7 × as long as maximal width (measured from base of membranous median suture to apex), marginally incurved at middle and close to apex; numerous dorsolateral setulae at middle gives a dense and fur-like appearance similar to G. lucida but the setulae are slightly longer. Surstylus slender, straight in caudal view; in lateral view tapering at base and distinctly arch-like bent in proximal 1/2, apex clavate and bent towards syncercus. Pregonite (Fig. 5C :iii) in caudal view rodlike; in lateral view lobe-like, with a characteristic wide and curved hook-like projection.

Aedeagus: Distiphallus in lateral view of almost uniform width.

Female (Figs 3C , 6A :iii, B:iii): Differs from male as follows:

Colouration: Fronto-orbital plate vivid metallic green when viewed from behind and slightly from above; the metallic ground colour continues down on the upper part of parafacial reaching the level of the lowermost frontal setae; the upper part of parafacial and anterior 1/3 of fronto-orbital plate with a thin greyish white microtomentum, visible along eye margin and as a slim line at edge of frontal vitta. Thorax and abdomen vivid metallic green at most with a thin whitish microtomentum.

Head (Fig. 3C ): Frons wider, at its narrowest point 0.76-0.93 (n = 12) × as wide as an eye in dorsal view. Frontal vitta gradually tapering towards ocellar tubercle, at this level often narrower than width of fronto-orbital plate. Fronto-orbital plate normally with fewer, 8-11 moderately strong medioclinate frontal setae. Outer vertical setae subequal with the ocellar setae, shorter than the posteriormost proclinate orbital setae, at least 2 × the length of the adjacent postocular setae. Postocellar setae short and tiny and subequal with the upper postocular setae. First flagellomere 1.38-1.62 (n = 8) × as long as pedicel; its maximum width 0.82-0.93 of the width of the parafacial at narrowest point.

Legs: Claws and pulvilli on fore legs shorter ca. 0.7-0.8 × as long as tarsal segment 5, the latter 1.5-1.7 × as long as tarsal segment 4.

Abdomen: Tergites 3 and 4 normally with two pairs of median discal setae, tergite 3 rarely missing one seta or with one additional seta, tergite 4 occasionally devoid of one seta. Ground vestiture dorsolateral on tergites 3 and 4 distinctly prone contrasting to the erect setulae between the median discal setae. Tergite 5 trapezoid, along anterior margin ca. 2 × as wide as long. Sternite 5 ca. as long as its maximal width, with 6-10 strong setae in posterior 1/3, four of them along the posterior margin and one or two pairs of median setae, in posterior 1/2 accompanied by numerous (60-70) irregularly spread setulae of varying size.

Terminalia (four dissections) (Fig. 6A :iii, B:iii): Tergite 6 in form of widely separated hemitergites; without tiny setulae in the adjacent posterior membranous area. Sternite 6 (Fig. 6A :iii) shorter 0.6-0.7 × as long as wide, slightly wider (1.1-1.2 ×) than sternite 5 and 1.8-1.9 × as wide as long, with 6-8 relatively strong setae along the posterior margin, accompanied by numerous (>20) tiny setulae. Tergite 7 strongly reduced, without tiny setulae in the adjacent membranous area. Sternite 7 slightly narrower than sternite 6, with numerous tiny setulae most of them restricted to the posterior margin. Sternite 8 reduced to a small faintly sclerotised plate with 6-12 sensory pores (sensilla trichodea). Hypoproct (Fig. 6B :iii) in ventral view distinctly rounded at apex (studied in ventral and somewhat caudal position somewhat blunt at apex): with a prominent depression, densely covered with short and tiny setulae, only a few in lateral position longer than the hypoproct itself; in lateral view not curved towards the cerci, apex of hypoproct reaching tip of cerci, lingulae well developed. Epiproct strongly reduced but in caudal view normally indicated by the presence of 2-4 setulae inserted between the cerci and above the hypoproct. Cerci reminiscent of a short-shafted paddle, weakly sclerotised with numerous setulae of varying length, in lateral view with some setulae that are subequal to the length of sternite 7 (twice the length of cerci itself).

DNA.

The European specimens of G. viridis share the Co1 DNA barcode sequence (BOLD:ACF3891) with Finnish G. zhelochovtsevi (Fig. 7 ).

Distribution.

A widely distributed and common species in the Palaearctic Region, including all of Europe, Japan (Hokkaido, Honshu), Middle East, all of Russia and Transcaucasia ( Richter 2004; O’Hara et al. 2009). It is possible that at least some northern records of the species, at least from the Taiga region in the Nordic countries, represent G. lucida .

Biology.

Gymnocheta viridis is a common spring-early summer species, often numerous at the right locations. Typical habitats include forest margins and meadows, but the species is frequently seen also in gardens. The males start their flight in early April in Central Europe and around end of April to early June in the north. The last female records in Finland are from mid-July. Males are frequently observed basking on tree trunks and watching for passing females. Both sexes can be collected from flowers, especially on cow parsnip ( Anthriscus sylvestris ), but also from other Daucaceae . The species is a known parasitoid of Erebidae ( Lepidoptera ) living in grass tufts, such as Mesapamea secalis Linnaeus and Photedes minima Haworth ( Tschorsnig 2017). The females can be frequently seen in meandering flight in the low vegetation and investigating tufts of grass or sedges in search for a host.

Figures

Figure 1. Gymnocheta spp. habitus A habitus Gymnocheta viridis ♂ B-E Tachina viridis Fallen, holotype specimen B dorsal view C head in lateral view. Note the protruding lower facial margin (arrowhead) D detail of the right wing edge. Note the reduced costal spine (arrowhead) E sternite 5 of the holotype F labels associated with the holotype. All photographs by Goeran Liljeberg.

Figure 2. Gymnocheta spp. male heads in lateral (upper panels) and dorsal (lower panels) view A Gymnocheta lucida Zimin B G. magna Zimin C G. viridis (Fallen) D G. zhelochovtsevi Zimin. Note the wide frons and strong outer vertical bristles. Scale bars: 1 mm. All photographs by Goeran Liljeberg.

Figure 3. Gymnocheta spp. female heads in lateral (upper panels) and dorsal (lower panels) view A Gymnocheta lucida Zimin B G. magna Zimin C G. viridis (Fallen) D G. zhelochovtsevi Zimin. Scale bars: 1 mm. All photographs by Goeran Liljeberg.

Figure 4. Fifth sternites of Gymnocheta spp. males A Gymnocheta lucida male abdomen. Note the narrow profile of the posterior edge of the fifth sternite (arrow) B the edge of the fifth sternite in G. viridis is bulky and protruding beyond the tip of the abdomen, clearly recognisable from the side C the posterolateral lobe of G. zhelochovtsevi is somewhat subrectangular as in G. magna, but more rounded in profile. Note the apical hook of the syncercus D in contrast to G. zhelochovtsevi, posterior edge of fifth sternite in G. porphyrophora with well-developed median lobes (arrow) E dissected fifth sternites of Nordic Gymnocheta spp. in comparison: i) G. lucida, ii) G. magna, iii) G. viridis and iv) G. zhelochovtsevi. A distinct dorsomedial process present in G. magna and G. viridis Abbreviations: bpl - basal plate; dmp - dorsomedial process; mcl - median cleft; pll - posterolateral lobe; tms - transversal median stripe; wll - wart-like lobe (or median lobe). Photograph D by V. Neimorovets, rest by J. Pohjoismaeki.

Figure 5. Comparison of Gymnocheta spp. male terminalia A lateral view of the terminalia: i G. lucida ii G. magna iii G. viridis and iv G. zhelochovtsevi - note the apical hook of the syncercus B dorsal view of the terminalia: i G. lucida ii G. magna iii G. viridis and iv G. zhelochovtsevi, same specimen as in Fig. 4 C C aedeagus and gonites of i G. lucida ii G. magna iii G. viridis and iv G. zhelochovtsevi. Abbreviations: bph - basiphallus; dph - distiphallus; prg - pregonite; pog - postgonite. All photographs by J. Pohjoismaeki.

Figure 6. Comparison of Gymnocheta spp. female sternites and terminalia A ventral view of the sternites and terminalia of i G. lucida ii G. magna iii G. viridis and iv G. zhelochovtsevi B detail of the female terminalia of i G. lucida ii G. magna iii G. viridis and iv G. zhelochovtsevi. Note the long cerci in G. zhelochovtsevi. All photographs by J. Pohjoismaeki.

Figure 7. Maximum likelihood tree of the Co 1 sequences of the Nordic Gymnocheta spp. and related Ernestiini. Numbers at nodes indicate posterior probabilities and scale bar the relative sequence divergence. BOLD progress ID given before the species name and sample ID as well as GenBank access number given after it. The DNA barcodes do not differ between the Nordic G. zhelochovtsevi and G. viridis (BOLD: ACA 6555) but differ significantly from G. lucida (BOLD: ACF 3891) and G. magna (BOLD: ACA 9848).