Stegana (Steganina) nigrita Malloch, 1924

Bächli, Gerhard & Vilela, Carlos R., 2022, On the identities of Neotropical Stegana species (Diptera, Drosophilidae). III. Four Costa Rican species described by J. R. Malloch, Revista Brasileira de Entomologia (e 20210113) 66 (1), pp. 1-23 : 7-10

Stegana (Steganina) nigrita Malloch, 1924

( Figs. 9-16 )

Stegana nigrita Malloch, 1924a: 97 (key, description). Malloch, 1924b: 1 (description); Heed, 1956: 61 (distribution); Heed, 1957: 76 (distribution); Wheeler, 1970: 79.6 (affiliation).

Stegana (Steganina) nigrita Malloch : Wheeler, 1981: 31 (affiliation); Brake and Bächli, 2008: 298 (affiliation).

Type locality: Costa Rica, Province of Alajuela, Canton of San Mateo, Higuito.

Diagnosis. Generally blackish flies without distinct pleural bands. Surstylus trapezoid, double-walled, outer wall devoid of a row of prensisetae, innerly covered with tiny wart-shaped scales, scarcely setose in the lower region; inner wall brush-like, as it is densely covered in the anteromedial area with ca. 40 strong, curved, sharp-tipped setae. Aedeagus spherical, ca. 1/3 length of aedeagal apodeme, membranous except for two strongly sclerotized anterodorsal curved plates, covered dorsodistally and ventrodistally with seta-like scales giving a serrate aspect to the margins; not coalescent to the aedeagal apodeme.Aedeagal apodeme long, curved, rod-shaped, anteriorly expanded dorsoventrally, almost three times as long as the aedeagus. Ventral rod submedially (not distally) positioned, strongly sclerotized, conspicuously fan-shaped, distally very wide and linked to the pouched gonopods by membranous tissue. Outer and inner paraphyses unrecognizable.

Material examined (n = 22).

Holotype ♀ [#24], dissected, labeled: “ Higuito / SanMateoCR [ Costa Rica] // PabloSchild / coll // Stegana / nigrita / Type [handwritten] / Det. / J R Malloch [printed] // Type No. / 26684 [handwritten] / U.S.N.M. [red label] // USNMENT / [QR code] / 01096615 [back side] // Stegana / nigrita Malloch / Bächli & Vilela det. 2017 // HOLOTYPE [red label] // ♀”. ( Figs. 9-12 ) . Paratypes ♂♂ [#34–43; #37, dissected]: same data as holotype, except sex and QR code; collector label missing in some such as in #37 . Non-type specimens ♂♂ [#48, #51, #52], ♀♀ [#44, #49, #50, #53–57]: labeled: “ La Suiza de / Turrialba Jul / COSTA RICA / Pablo Schild // ALMelander / Collection / 1961 // USNMENT / [QR Code] / 013… [back side] // #..”

Comments. Malloch (1924b) listed one male holotype and ten paratypes. Indeed, the type specimen series we received contains 11 specimens; one female labeled “type” and ten males labeled “ paratype ”.

Redescription

♂. (n = 13). Head ( Fig. 13 ) generally blackish. Frontal length 0.475 (0.39–0.51) mm; frontal index about 1.69 (1.35–1.92), top to bottom width ratio about 1.41 (1.24–1.54). Frontal triangle hardly visible, about 40% of frontal length; ocellar triangle prominent, about 35% of the frontal length. Orbital plates paler grayish, about 60% of frontal length, orbital setae arranged in a row, distance of or3 to or2 about 64% of or3 to or1, distance of or2 to or1 about 36% of or3 to or1, distance of or3 to or1 about 220% of or3 to vtm, or1 / or3 ratio about 1.03 (0.90–1.17), or2 / or1 ratio about 0.76 (0.63–0.86), vt index about 0.89 (0.79–0.95), postocellar setae about 24 (20–29) % of frontal length, ocellar setae about 69 (58–79) % of frontal length; vibrissal index about 0.41 (0.31–0.47). Face blackish. Carina indistinct, short, flat. Cheek linear, narrow, brownish, index about 17 (12–23). Eye roundish, with main axis almost vertical, index about 1.24 (1.14–1.35). Pedicel yellowish, dorsally blackish, flagellomere 1 blackish, length to width ratio about 1.76 (1.38–2.00). Arista has 5-7 dorsal, 5-7 ventral and about 6 small inner branches, plus a short terminal fork. Proboscis brownish. Palpus black, somewhat broader medially.

Thorax ( Fig. 13 ) generally blackish, length about 1.35 (1.10–1.67) mm. Scutum with about 8 rows of acrostichal setae, one postpronotal seta; dc index about 0.44 (0.33–0.50). Scutellum slightly pointed, distance between apical scutellars about 75% of the apical to the basal one; basal ones divergent, apical ones crossed; scut index about 1.42 (1.25–1.65). Pleura ( Fig. 13b ) generally blackish but paler towards the lower margin, no distinct horizontal dark stripes visible, sterno index about 0.92 (0.85–1.00). Halter with black knob. Legs ( Fig. 13a,b,d ) generally blackish, knees and tips of tibiae paler, all tarsi yellowish.

Wing ( Fig.13 ) generally dark brown, somewhat paler towards the hind margin, m 3 apically slightly bent upwards, length 2.14 (1.82–2.45) mm, length to width ratio about 1.86 (1.54–2.07). Indices: C = 1.85 (1.70–2.00), ac = 9 (7–10), hb = 0.71 (0.64–0.80),4C = 1.32(1.17–1.46), 4v = 1.86 (1.59–2.08), 5x = 1.07 (0.89–1.29), M = 0.59 (0.50–0.69), prox. x = 0.99 (0.83–1.25).

Abdomen ( Fig. 13d ) shining blackish.

Terminalia ( Figs. 14–16 ). Epandrium microtrichose ( Fig. 14 ), with 17 (left) or 13 (right) upper and 12 (left) or 18 (right) lower setae; upper setae in two parallel curved rows adjacent to the posterior margin, setae of posterior row longer, lower setae scattered over the ventral region that is neither in a ventral lobe form nor covering the surstylus. Cercus ( Fig. 14b,c ) reduced to a narrow vertical stripe, setose, not microtrichose, without ventral lobe and anteriorly linked to epandrium by membranous tissue. Surstylus trapezoid-shaped in the lateral view ( Fig. 14a ), double-walled, outer wall covered with tiny wart-shaped scales and scarcely setose in the lower region, inner wall brush-like, densely covered in the anteromedial area with ca. 40 strong, curved, sharply-tipped setae ( Fig. 14b,d ), probably functioning as prensisetae which are absent on the inner margin; base of surstylus weakly linked to epandrium by membranous tissue. Decasternum ( Fig. 14c ) slightly sclerotized, strip shaped. Hypandrium sinuate in lateral view ( Fig.15a ), triangular in anterior and posterior views, slightly wider than long, as long as the epandrium, anterior margin convex, posterior margin medially concave ( Fig.15b ); posterior hypandrial process absent; dorsal arch sclerotized, distally sinuate in the anterior and posterior views, laterally perpendicular and widely fused to the posterior hypandrium arms, bearing a deep concavity ( Fig.15b ), where well-developed surstyli rest, dorsodistally projected forwards as a half pear-shaped tube dorsally sheltering the aedeagus ( Fig. 15a ); gonopods fused to each other and the posterior margin of the hypandrium, perpendicular to the hypandrium, bare and concave as a shallow pouch ( Fig. 15b ) where the aedeagus rests. Aedeagus ( Figs. 15 , 16 ) relatively small, somewhat spherical, membranous except for two strongly sclerotized anterodorsal curved plates (probably inner paraphyses fused to the aedeagus), covered dorsodistally ( Fig.16a ) and ventrodistally ( Fig.16e ) with seta-like scales, which are dorsally shorter and ventrally longer giving a serrate aspect to the margins in the lateral view ( Fig. 16c ); base of aedeagus linked to the aedeagal apodeme by membranous tissue. Aedeagal apodeme ( Figs. 15 , 16 ) long, curved ( Fig.16c ), rod-shaped, anteriorly expanded dorsoventrally ( Fig. 16c ), almost three times as long as the aedeagus. Ventral rod submedially (not distally) positioned, strongly sclerotized, crosswise flattened, conspicuously fan-shaped ( Figs. 15b , 16 ), distally very wide and linked to the pouched-like gonopods by membranous tissue ( Fig. 15b ). Outer and inner paraphyses not recognizable, probably either lost or fused to the ventral rod and aedeagus, respectively.

♀. (n = 9). Differences compared to males: No obvious differences in external morphology ( Figs. 10 , 11 ). Measurements: Frontal length about 0.42 (0.32–0.46) mm, frontal index about 1.46 (1.19–1.63), top to bottom width ratio about 1.32 (1.21–1.50), or1 / or3 ratio about 1.08 (0.93–1.67), or2 / or1 ratio about 0.81 (0.60–0.93), postocellar setae about 30 (22–35) % of the frontal length, ocellar setae about 79 (70–85) % of the frontal length; vt index about 0.89 (0.79–1.00). vibrissal index about 0.37 (0.32–0.47), Cheek index about 17 (9–24). Eye index about 1.25 (1.18–1.38). Flagellomere 1 ratio about 1.74 (1.63–1.86).

Thorax length about1.28 (0.79–1.60) mm; dc index about0.44 (0.33–0.50), scut index about 1.42 (1.25–1.65), sterno index about 0.92 (0.85–1.00).

Wing length = 2.11 (1.64–2.45) mm.Indices: C index = 1.90 (1.78–2.19), ac = 8 (7–9), hb = 0.69 (0.61–0.77),4C = 1.27 (1.17–1.42), 4v = 1.86 (1.67–2.00), 5x = 1.08 (0.89–1.20), M = 0.56 (0.47–0.67), prox. X = 1.01 (0.86–1.25).

Terminalia (n = 1) ( Fig. 12 ). One pair of short cerci inserted beyond and between the epiproct and hypoproct.Oviscapt valves absent, sternite 8 (egg guide of Laštovka and Máca, 1982) horizontally positioned, not protruding beyond the hypoproct, and somewhat rectangle-shaped; posterior margin with a deep V-shaped notch conspicuously bordered with 14 short, strongly sclerotized, sharply pointed, peg-shaped ovisensilla in addition to 16 similar ones, arranged somewhat in adjacent line. Spermathecal capsule bulbous, with a long-tailed appendage ( Laštovka and Máca, 1982); height slightly shorter than sternite 8.

Distribution. Costa Rica (Provinces of Alajuela and Cartago)

Biology. Unknown.

Figures

Figure 9 Stegana nigrita Malloch, 1924, labels of female holotype #24.

Figure 10 Stegana nigrita Malloch, 1924, female holotype #24, Higuito, San Mateo,Alajuela,Costa Rica [Type Number 26684, USNM], habitus, four views:a, oblique dorsal,b, left lateral, c, thorax and wings dorsal, d, abdomen dorsal.Scale bar = 1 mm.

Figure 11 Stegana nigrita Malloch, 1924, female holotype #24, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26684, USNM], habitus, three close-up views: a, head left lateral, b, head frontodorsal, c, left wing ventral.Scale bars = 1 mm; a and b, to the same scale.

Figure 12 Stegana nigrita Malloch, 1924, female holotype #24, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26684, USNM], terminalia [inset = inner spermathecal capsule in focus], ventral view. Scale bar = 0.1 mm.

Figure 13 Stegana nigrita Malloch, 1924, male paratype #37, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26684, USNM], habitus, four views: a, oblique dorsal, b, left lateral, c, thorax and wings dorsal, d, abdomen dorsal. Scale bar = 1 mm.

Figure 14 Stegana nigrita Malloch, 1924,male paratype #37, Higuito, San Mateo,Alajuela,Costa Rica [Type Number 26684,USNM],external terminalia, four views:a, epandrium, surstylus, and cercus, left lateral, b, epandrium, surstyli, and cerci, oblique posterior, c, idem, posterior, d, idem, anterior [left surstylus inner wall in focus]. Scale bar = 0.1 mm.

Figure 15 Stegana nigrita Malloch,1924, male paratype #37, Higuito,San Mateo,Alajuela,Costa Rica [Type Number 26684, USNM],internal terminalia,four views:a, hypandrium, aedeagus, gonopod, and aedeagal apodeme, left lateral, b, hypandrium, aedeagus, fused gonopods [perpendicular to the hypandrium], and aedeagal apodeme, oblique posterior, c, idem, oblique ventral, d, idem, ventral. Scale bar = 0.1 mm.

Figure 16 Stegana nigrita Malloch, 1924,male paratype #37, Higuito, San Mateo, Alajuela,Costa Rica [Type Number 26684, USNM],five views of the aedeagus,aedeagal apodeme, and ventral rod, from dorsal through ventral. Scale bar = 0.1 mm.