Stegana (Steganina) atrimana 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 : 2-7

Stegana (Steganina) atrimana Malloch, 1924

( Figs. 1-8 )

Stegana atrimana Malloch, 1924a: 97 (key, description); Malloch, 1924b: 2 (description); Wheeler, 1970: 79.6 (affiliation).

Stegana (Steganina) atrimana Malloch : Wheeler, 1981: 31 (affiliation); Brake and Bächli, 2008: 296 (affiliation).

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

Diagnosis. Generally brownish, shining flies. Eyes roundish, main axis almost vertical. Front pale with dark orbital plates. Gena narrow. Pleura pale with two distinct black longitudinal bands. Male fore tarsi somewhat laterally compressed, tarsomeres 1–4 black, apical joint yellow. Surstylus finger-shaped, double-walled, with many setae adjacent to the inner margin of both the outer and inner wall, bearing just one short, sharp, subterminal prensiseta on the lower margin, not microtrichose, and anteriorly fused in a right angle to decasternum. Decasternum transverse, circumflex-shaped, curved posterad, densely covered with ca. 40 strong, curved, sharply tipped setae, laterally fused in a right angle to the anterior region of the surstylus. Gonopods sclerotized, distally fused to outer paraphyses, proximally somewhat concave, curved strip-shaped, fused to each other and articulated to the posterior hypandrial process by membranous tissue, devoid of seta. Aedeagus ca. 1/2 length of aedeagal apodeme, and not coalescent to it, distally covered with blunt, seta-like scales, anterior ones short, the posteromarginal ones conspicuously long, distally 3- or 4-branched (longest ones), conspicuously fringe-shaped.Outer paraphysis folded over itself, knee-shaped in the lateral view, medianly bearing 6 tiny setulae.

Material examined (n = 4).

Holotype ♀ [#22], dissected, labeled ( Fig. 1 ): “ Higuito / SanMateoCR [ Costa Rica] // PabloSchild / Coll // Stegana / atrimana / Type [handwritten] / Det./ J R Malloch [printed] // Type No./ 26683 [handwritten] / U.S.N.M. [red label] // USNMENT / [QR Code] / 01383629 [back side] // Stegana / atrimana Malloch / Bächli & Vilela det. 2017 / HOLOTYPE [red label] // ♀” . Paratypes ♂♂ [#11, #12; latter dissected] and non-type ♂ [#10]: same data as holotype, except for type status, sex and QR code .

Comments. Malloch (1924b) listed one male holotype and two female paratypes. However, the type series we received contains one female holotype [labeled Type] and two male paratypes.

Redescription

♂. (n = 3). Head ( Fig. 5 ) is generally yellowish.Frons glossy brownish, paler medially and above antennae. Frontal length 0.48 (0.44–0.51) mm; frontal index about 1.83 (1.76–1.87), top to bottom width ratio = 1.57 (1.53–1.60); frontal triangle hardly visible, about 33–44% of frontal length; ocellar triangle black, slightly prominent, about 26–35% of frontal length. Orbital plates apically slightly diverging from the eye margin, about 64–73% of frontal length. Orbital setae arranged in a row, distance of or3 to or2 about 55% of or3 to or1, distance of or2 to or1 about 45% of or3 to or1, distance of or3 to or1 about 220% of or3 to vtm, or1 / or3 ratio = 1.09 (1.00–1.21), or2 / or1 ratio = 0.67 (0.63–0.71), vt index = 0.96 (0.93–1.00), postocellar setae crossed, about 22 (17–27) % of frontal length, ocellar setae = 56 (50–65) % of frontal length; vibrissal index = 0.24. Face pale yellowish, with a brown spot above mouth margin. Carina narrow, prominent in the upper half of the face. Cheek whitish, broadened backwards, index about 8 (6–9). Eye oblong, main axis slightly oblique, index about 1.11 (1.06–1.14).Occiput black at about upper half, white below. Pedicel yellowish. Flagellomere 1 black, length to width ratio about 1.74 (1.50–2.00). Arista has 7 dorsal, 6 ventral and about 6 rather long inner branches, plus a short terminal fork.Proboscis and palpus yellowish.

Thorax ( Fig.4 a-c) length about 1.36 (1.19–1.40) mm. Scutum slightly micropubescent, brownish, paler in anterior area and on postpronotum, with diffuse pale stripes outside dc lines, 8 rows of acrostichal setae. Transverse distance of dorsocentral setae about six times the longitudinal distance; dc index about 0.30.Scutellum almost roundish, brownish, with paler margin, scutellar setae almost equidistant; basal setae divergent, apical ones crossed: scut index about 1.65 (1.56–1.75). Pleura whitish, with a broad, black, horizontal stripe ( Fig. 4b ) in the upper half and a lower, narrower, brown, horizontal stripe above the middle of the katepisternum joining the upper stripe around the haltere, sterno index about 0.82 (0,79-0.84).Haltere with a black knob.Legs generally yellowish, fe 1 in basal half blackish, apically with 2–3 strong setae below, ti1 black with short pale base and tip, fe2 and ti2 black with a pale knee, fore tarsi slightly laterally compressed, tarsomeres 1–4 black, tarsomere 5 pale.

Wing ( Fig. 4 ) slightly pointed, generally brownish but becoming paler towards hind margin, c 3 with about 7 warts below, r 2+3 apically bent towards costa, m 3 straight, ending close to r 2+3, wing length about 2.09 (1.92–2.31) mm, length to width ratio about 1.81 (1.77–1.83). Indices: C = 1.70 (1.62–1.76), ac = 8 (7–9), hb = 0.73 (0.71–0.76), 4C = 1.44 (1.38–1.55), 4v = 1.96 (1.80–2.18), 5x = 1.10 (1.00–1.17), M = 0.60 (0.53–0.64), prox. x =0.98 (0.77–1.18).

Abdomen ( Fig.4d ) shining brownish, hind margins of tergites blackish.

Terminalia ( Figs. 6–8 ). Epandrium setose and macrotrichose, except for the vestigial lobe, dorsally destroyed [probably eaten by psocopterans as their feces were stuck to the specimen body], setae adjacent to distal margin longer; ventral lobe vestigial, partially covering the surstylus’ proximal area. Surstylus ( Fig. 6a–c ), finger-shaped, double-walled, with many setae adjacent to the inner margin of both the outer and inner wall, bearing just one short, sharp, subterminal prensiseta on the lower margin inner wall, not microtrichose, anteriorly fused in a right angle to the decasternum; weakly linked to the epandrium by membranous tissue. Decasternum circumflex-shaped in the anterior ( Fig. 6b ) and posterior ( Fig. 6a ) views, curved posterad, laterally fused in a right angle to the anterior region of the surstylus ( Fig. 6c ), densely covered with ca. 40 strong, curved, sharply-tipped setae, probably functioning as a prensisetae which are scarce (just one) on the inner margin of the surstylus. Cercus reduced to a narrow vertical stripe, dorsally destroyed, setose, not microtrichose, without ventral lobe, anteriorly linked to the epandrium by membranous tissue. Hypandrium sinuate in the lateral view ( Fig. 7c ), lozenge-shaped in the dorsal and ventral views ( Fig. 7a, b ), as long as wide, anterior margin strongly convex, posterior margin concave; posterior hypandrial process short; dorsal arch sclerotized, mediodistally projected dorsad, dorsodistally slightly projected backwards as a half cylinder, medially strongly narrow sheathshaped (probably originated from fused inner paraphyses) dorsally embracing the aedeagus ( Fig. 7c ); gonopods sclerotized, proximally curved strip-shaped ( Fig. 7d ), anteriorly fused to each other ( Fig. 7b ), articulated by membranous tissue to posterior hypandrial process; distally fused to outer paraphysis ( Fig. 7c ), devoid of seta. Aedeagus ( Figs. 7 a-d, 8) relatively small (ca. 1/2 length of aedeagal apodeme), somewhat similar to that of S. tempifera ( Fig. 31 ), triangular in lateral view [as in S. tempifera ], circular in dorsal and ventral views ( Fig. 8a,e ) [elliptical in S. tempifera ; Fig. 31a,e )], distally covered with blunt, seta like scales, anterior ones short, posteromarginal ones conspicuously long, distally 3- or 4-branched (longest ones; Fig. 8 ), conspicuously fringe-shaped; aedeagus linked to aedeagal apodeme by membranous tissue. Aedeagal apodeme rod-shaped, distally slightly curved and expanded laterad, twice as long as aedeagus. Ventral rod not recognizable (clearly recognizable in S. tempifera ) between outer paraphyses. Outer paraphysis proximally divergent, perpendicular to aedeagus, concave ( Fig. 8 c-e) and mostly membranous, distally double-walled ( Fig. 7a ), folded over itself (knee-shaped in lateral view; Fig. 7c ), ear-shaped in posterior view, strongly sclerotized ( Fig. 7a, b ) and widely fused to curved strip-shaped gonopod, medianly bearing 6 tiny setulae ( Fig. 7b ); inner paraphysis not recognizable, probably fused to form a dorsal arch (as interpreted by Laštovka and Máca, 1982) or just its distal part, sheltering the aedeagus. Ejaculatory apodeme ( Figs. 6d , 7e, f ) strongly sclerotized, somewhat similar in profile to the generalized tripunctata type of genus Drosophila as proposed by Throckmorton (1962: 242, fig. 19.34); in the lateral view ( Fig. 7e ), plate ca.77% handle length, and handle ca. 70% of the aedeagal apodeme length ( Fig. 7c ), inner angle ( Fig. 7e ) between the handle and plate> 90°; plate spatulate, longer than wide, in the posterior view ( Fig. 7f ).

♀. Differences compared to males:No obvious differences in external morphology ( Fig. 2 ). Measurements: Frontal length about 0.46 mm. Frontal index about 1.80, top to bottom width ratio about 1.47. Frontal triangle about 30% of frontal length; ocellar triangle about 45% of frontal length. Orbital plates about 65% of the frontal length.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 135% of or3 to vtm, or1 / or3 ratio about 1.17, or2 / or1 ratio about 0.86, postocellar setae about 25% of frontal length, ocellar setae about 52% of frontal length; vt index about 0.80, vibrissal index about 0.30. Cheek index about 8. Eye index about 1.14. Flagellomere 1 ratio about 2.00.

Thorax length about 1.50 mm. Transverse distance of dorsocentral setae about 480% of their longitudinal distance; dc index about 0.36, scut index about 1.96, sterno index about 0.73. Wing length about 2 mm. Indices: C = 1.79, ac = 9.5, hb = 0.53, 4C = 1.46, 4v = 2.00, 5x = 1.14, M = 0.62, prox. X = 1.08.

Terminalia ( Fig. 3 ). One pair of finger-shaped cerci inserted beyond and between the epiproct and hypoproct (subanal plate of Laštovka and Máca, 1982). Oviscapt valves absent, sternite 8 (egg guide of Okada, 1971 and Laštovka and Máca, 1982) horizontally positioned, somewhat rectangle-shaped, posterior margin with a shallow median notch, and not protruding. It is devoid of a peg-shaped ovisensilla, and its trichoid ovisensilla seem to be similar to those of the preceding sternites, except for the distal notch. Inner spermathecal capsule ( Fig. 3 , and inset) somewhat spherical, mostly papillate, distally bearing a long-tailed appendage ( Laštovka and Máca, 1982), devoid of basal and apical introverts; height slightly shorter than sternite 8.

Distribution. Costa Rica (Province of Alajuela).

Biology. Unknown.

Figures

Figure 1 Stegana atrimana Malloch, 1924, labels of female holotype #22.

Figure 2 Stegana atrimana Malloch, 1924, female holotype #22, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26683, USNM], habitus, four views: a, oblique dorsal, b, left lateral, c, head and thorax dorsal, d, abdomen dorsal.Scale bar = 1 mm.

Figure 3 Stegana atrimana Malloch, 1924, female holotype #22, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26683, USNM], terminalia [inset = inner spermathecal capsule in focus], left oblique lateral view. Scale bar = 0.1 mm.

Figure 4 Stegana atrimana Malloch, 1924, male paratype #12, Higuito, San Mateo, Alajuela, Costa Rica [Paratype Number 26683, USNM],habitus, four views: a, oblique dorsal, b, left lateral, c, thorax dorsal, d, abdomen dorsal. Scale bar = 1 mm.

Figure 5 Stegana atrimana Malloch, 1924, male paratype #12, Higuito, San Mateo, Alajuela, Costa Rica [Paratype Number 26683, USNM], habitus, two close-up views: a, head dorsal, b, head frontodorsal. Scale bar = 1 mm.

Figure 6 Stegana atrimana Malloch, 1924, male paratype #12, Higuito, San Mateo, Alajuela, Costa Rica [Paratype Number 26683, USNM], external terminalia and ejaculatory apodeme:a, epandrium [dorsally damaged], surstylus, and cerci,posterior view, b, idem, anterior view, c, decasternum and surstyli, ventral view, d, ejaculatory apodeme,oblique posterior view.Scale bar = 0.1 mm.

Figure 7 Stegana atrimana Malloch, 1924, male paratype #12, Higuito, San Mateo, Alajuela, Costa Rica [Paratype Number 26683, USNM], internal terminalia, several views: a, hypandrium,aedeagus, and outer paraphyses+gonopods, dorsoposterior, b, idem plus the aedeagal apodeme,posterior,c, idem, left lateral, d, idem, antero-oblique, e, ejaculatory apodeme, left lateral view of the handle and plate, f, idem, posterior view of the handle and plate. Scale bar = 0.1 mm.

Figure 8 Stegana atrimana Malloch, 1924, male paratype #12, Higuito, San Mateo, Alajuela, Costa Rica [Paratype Number 26683, USNM], five views of the aedeagus, aedeagal apodeme, and ventral rod, from dorsal through ventral. Scale bar = 0.1 mm.

Figure 31 Stegana tempifera Malloch, 1924, male holotype #23, Higuito, San Mateo, Alajuela, Costa Rica [Type Number 26680, USNM], five views of the aedeagus, aedeagal apodeme, ventral rod, and outer paraphyses, from dorsal through ventral. Scale bar = 0.1 mm.