Risa Becker, 1907

Mathis, Wayne N. & Zatwarnicki, Tadeusz, 2023, Phylogeny and Taxonomy of the Risa Genus-group (Diptera: Ephydridae), with Description of a New Genus from Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (1), pp. 1-23 : 10-12

Genus Risa Becker

Risa Becker, 1907:404 . Type species: Risa longirostris Becker, 1907:404 [monotypy]. Hennig, 1937:75 [redescription]. Papp, 1984: 178 [Palearctic catalogue]. Griffiths, 1990: 128 [phylogenetic discussion]. Mathis & Zatwarnicki, 1998:550 [generic key]. Kotrba & Mathis, 2009: 627–640 [morphology of female terminalia]. D. K. McAlpine, 2002: 5–6; 2011: 9–10 [antennal morphology].

Diagnosis. Minute to small shore flies, body length 0.95–1.60 mm; generally dark colored, shiny; mouthparts geniculate, moderately to extremely long; wing venation reduced.

Head: Generally bluish black to black, somewhat shiny ( Figs 26, 27 , 35, 37–41 , 49, 50 , 57–60 ). Frons generally black, shiny; ocellar triangle long and narrow, extended to anterior margin of frons; ocellar setae well developed, proclinate, slightly divergent; pseudopostocellar setulae divergent; both medial and lateral vertical setae well developed; fronto-orbital setae 2–4, usually 3, orientation various: in most species all fronto-orbital setae proclinate ( Figs 21, 22 , 35–41 , 46, 49, 50 , 57–60 ), small, hair-like, subequal (“similar” in text hereafter); in some species anterior fronto-orbital seta about 2–3 times longer than middle seta, inclinate, posterior seta usually reclinate (“dissimilar” in text hereafter; R. flavipalpis is intermediate), frons otherwise with few setulae above and near antennal base. Antenna short to moderately elongate; antennal ratio ⅓–⅔; basal flagellomere ratio varying from only slightly greater than 1:4; usually predominantly yellow, frequently brownish dorsoapically; pedicel elongate with lobe on medial side of dorsal seam more prominent than on lateral side; distal articular surface less deeply concave, lacking any suggestion of a cup-like cavity; conus relatively narrow but strongly projected, arising close to medial dorsal lobe; foramen faces laterally; basal flagellomere has no basal stem, basal foramen on a slight scabrous prominence on lateral margin of basal hollow, hollow capacious tilted medially, and its floor with a narrow caecum-like extension; pore of sacculus in a ventral position; beyond base of arista; pedicel lacking a well-developed, spine-like seta anterodorsally; arista about as long as antenna, rather thick at base, bearing short to very short, dorsal hair-like branches. Face vertically carinate, carina prominent to shallow, in lateral view sharp to rounded ( Figs 23–27 , 35–41 , 46, 49, 50 ); facial seta 1; ventral facial margin arched. Eye vertically oval, higher than wide, appearing bare. Gena short; 1 genal seta. Clypeus not exposed. Proboscis geniculate, rostrum elongate ( Figs 23–25 ), haustellum and labellum equal in length, but labellar ratio variable among species; 2–3 pseudotracheae, these short, at apex of labellum ( Figs 31, 32 ); cibarium with 2 medial sensillae ( Fig. 29 ) and no ventral sensillae; palpus black or yellow.

Thorax: Mesonotum generally dark bluish or greenish black to black; scutellum wider than long. Chaetotaxy as follows: Acrostichal setulae in 2 irregular rows ( Figs 39 , 59, 60 ), sometimes with 1 well-developed, prescutellar pair; only posteriormost dorsocentral seta well developed; 1 postpronotal seta; 1 presutural supra-alar seta; 1 postsutural supra-alar seta; 1 postalar seta; 2 notopleural setae; 2 marginal scutellar setae; 1 proepisternal seta, 1 proepimeral seta, 1–2 anepisternal setae, one or both along posterior margin, if 2, ventral seta longer; 1 katepisternal seta ( Fig. 60 ). Wing generally milky white, not darkened at base or elsewhere; costa short, extended to apex of vein R 4+5; vein R 2+3 well separated from costa; vein R 4+5 short, reaching costa far anterior of wing tip; vein M reaching wing tip or slightly posterior; R stem vein lacking setulae dorsally; veins M and CuA 1 colorless; crossvein dm–cu absent ( Fig. 9 ); costal setulae arranged in 2 more or less equal rows (anterodorsal and anteroventral rows). There are either less and sparser setulae (up to about 35 along distalmost section of costa), or setulae are numerous and dense (more than 40 on distalmost section of costa). Halter variable, whitish yellow to blackish. Coxae, trochanters, and femora dark brown to black except apices of femora usually yellow; tibiae centrally usually brown to black but extent of dark coloration varies between legs as well as inter- and intraspecifically; mid- and hindtibiae usually more extensively dark than foretibia; tarsi yellow.

Abdomen: Generally dark bluish or greenish black to black, sometimes partly orange basally. Male: Tergites and sternites 1–5 well developed, each tergite with a spiracle in ventral margin; spiracle 6 in membrane adjacent to postabdomen; sternite 2 notched or excavated along anterior margin or distinctly Y-shaped, with arms of bifurcation oriented anteriorly. Male terminalia: Epandrium as an inverted U, narrowed dorsally, band-like, lateral arms becoming wider ventrally ( Figs 42 , 51 , 61 ); cercus elongate, bacilliform, setulose, sometimes somewhat fused ventrolaterally with medial margin of epandrium; gonostylus well developed ( Figs 51, 55 ) or fused with ventral margin of epandrium ( Figs 61, 62 ); pregonite attached to subepandrial plate, variously developed, short or long, narrow, sharply pointed apically; subepandrial plate partially attached to underside of epandrium; postgonite attached to aedeagus-phallapodeme complex, mostly rounded ( Figs 44, 45 , 53, 54 , 63, 64 ), sometimes with narrow process, bearing 3–4 setulae ( Figs 63, 64 ); aedeagus and phallapodeme broadly fused at juncture; aedeagus a simple tube, rounded apically; phallapodeme short, lacking extended keel; hypandrium well developed, attached posterolaterally to epandrium, broad, emarginate medially at base, shallowly concave, sometimes weakly sclerotized ( Figs 44, 45 , 53, 54 , 63, 64 ). Female terminalia: Subanal plate absent; sternite 8 entire but lacking a sclerotized, protrusion, posterior portion lacking hooked setulae, but bearing 12–22 short, straight setae along anterior margin; cerci short and rounded ( Fig. 33 ); stalk of ventral receptacle with ( Figs 47, 48 ) or without ( Fig. 15 ) paired, tubular processes.

Distribution and natural history. Risa is strictly an

Old World genus, now comprising ten described species. The geographic range for the genus extends from Spain and Morocco eastward across North Africa and Israel to Mongolia in the far east. The genus seems to be restricted to arid regions where it is associated with host plants of the family Amaranthaceae .

Discussion. The female terminalia of Risa are peculiar and are a primary source of evidence, supporting the inclusion of this genus in the Ephydridae . This combination of characters is not known to occur in any other family of Schizophora. In freshly pinned material it is possible to see a row of white hairs that requires high magnification for clarification of its structure (SEM?). The structure and sclerotization of the female terminalia are such that even in shriveled specimens the apex of the abdomen is exposed and more or less in a natural position. In shriveled males, the lateral margins of the abdomen fold such that the abdomen appears triangular and the terminalia are hidden behind the folds.

The monophyly of Risa is corroborated by the following characters that are mostly synapomorphies (many of these characters were identified previously by Griffith, 1972; D. K. McAlpine, 2002, 2011): Head: Reclinate fronto-orbital seta reduced or lacking; pore of the sacculus in a ventral position on the basal flagellomere; face distinctly carinate, sometimes carina somewhat pointed; mouthparts moderately to distinctly geniculate; elongate prementum of the proboscis; labellum equal to haustellum. Thorax: Wing often milky white; costa short, extended to vein R 4+5; subcosta fused with R 1 distally; crossvein dm–cu absent.

The proboscis in species of Risa is elongated, which is apparently an adaptation to nectar feeding as adults. Similar adaptations of the proboscis have developed in the Milichiidae , hence the placement of Risa by some authors in this family (see illustrations and descriptions in the seminal work of Brake, 2000).

Figures

Figures 26–33. Photographs of Risa longirostris Becker (26–27, 29–31, 33) and Risa brevirostris sp. nov. (28, 32). (26) Head, anterooblique view. (27) Same, anterior view. (28) Proboscis, lateral view. (29) Rostrum, anterior view (microscopic photograph). (30) Same, lateral view. (31) Labellum, posterior view. (32) Labellum, anterior view. (33) Terminal female abdominal segments, anterior view. Scale bars = 0.2 mm (26–27), = 0.1 mm (28–30, 33), = 0.05 mm (31–32).

Figures 34–37. Line drawing and photographs of Risa. (34) Terminal female abdominal segments of R. brevirostris sp. nov., anterior view. (35) Habitus of R. brevicornis (Papp), antero-oblique view. (36) Head of R. brevirostris sp. nov., lateral view. (37) Habitus of R. salsolae (Mathis & Zatwarnicki), antero-oblique view. Scale bars = 0.1 mm (34), = 0.2 mm (35, 37).

Figures 38–41. Photographs of Risa brevirostris sp. nov. (38–39) and R. longirostris Becker (40–41). (38) Head, anterior view. (39) Same, dorso-oblique view. (40) Habitus, lateral view. (41) Head, antero-oblique view. Scale bars = 0.1 mm (38–39), = 0.2 mm (40–41).

Figures 46–50. Line drawing and photographs of Risa nettae sp. nov. (46) Head, lateral view. (47) Ventral receptacle, lateral view (microscopic photograph). (48) Ventral receptacle, posterior view (microscopic photograph). (49) Head, anterior view.(50) Same, laterooblique view. Scale bars = 0.05 mm (47–48), = 0.2 mm (49–50).

Figures 57–60. Photographs of Risa kotrbae sp. nov. (57) Head, anterior view. (58) Head and thorax, lateral view. (59) Same, dorsal view. (60) Same, dorsolatero-oblique view. Scale bars = 0.2 mm (57), = 0.5 mm (58–60).

Figures 20–25. Line drawing of frons and associated setae, dorsal view. (20) Notorisa mcalpinei sp. nov. (21) Risa longirostris Becker. (22) R. asiatica Ozerov. (23–25) Line drawing of head, lateral view. (23) R. longirostris Becker. (24) R. brevicornis Papp. (25) R. longicornuta Papp.

Figures 6–9. Photographs of Notorisa mcalpinei sp. nov. (6–8) and Risa longirostris Becker (9). (6) Head, thorax and abdomen, anterooblique view. (7) Head, lateral view. (8) Wing. (9) Wing. Scale bars = 0.5 mm.

Figures 42–45. Male terminalia of Risa brevirostris sp. nov. (42) Epandrium, cerci, gonostylus, subepandrial plate with pregonites, ventral view. (43) Same, lateral view. (44) Internal structures (postgonite, hypandrium and aedeagus fused with phallapodeme), ventral view. (45) Same, lateral view. Scale bar = 0.1 mm.

Figures 51–56. Male terminalia of Risa nettae sp. nov. (51) Epandrium, cerci, gonostylus, subepandrial plate with pregonites, ventral view. (52) Same, lateral view. (53) Internal structures (postgonite, hypandrium and aedeagus fused with phallapodeme), ventral view. (54) Same, lateral view. (55) Anterior section of epandrium and cerci, gonostylus (without supepandrial plate and pregonites), ventral view. (56) Subepandrial plate and pregonites, lateral view. Scale bar = 0.1 mm.

Figures 61–64. Male terminalia of Risa kotrbae sp. nov. (61). Epandrium, cerci, gonostylus, ventral view. (62) Same, lateral view. (63) Internal structures (postgonite,hypandrium and aedeagusfused withphallapodeme),ventral view.(64)Same,lateral view.Scalebar =0.1 mm.

Figures 10–15. Photographs of Notorisa mcalpinei sp. nov. (10–14) and Risa longirostris Becker (15). (10) Proboscis, lateral view. (11) Labrum, posterior view. (12) Cibarium, posterior view. (13) Terminal female abdominal segments, ventral view. (14) Ventral receptacle, lateral view. (15) Ventral receptacle, lateral view. Scale bars = 0.2 mm (10–11), = 0.1 mm (12–13), = 0.05 mm (14–15).