On the identities of Neotropical Stegana species (Diptera, Drosophilidae). II. Stegana acutangula (Hendel) and Stegana triseta (Duda), with descriptions of three new closely related species

Stegana (Orthostegana) acutangula (Hendel) from Bolivia and Stegana (Steganina) triseta (Duda) from Costa Rica are redescribed based on type specimens, and their identities clarified. A single syntype male of the first species (type species of the subgenus Orthostegana) is designated as a lectotype and one male out of the four Costa Rican syntypes (3 males, 1 female) of the latter species was selected as a lectotype of the Steganina subgenus. The other three (2 males, 1 female) specimens were designated as paralectotypes. All four males were dissected and their terminalia were photomicrographed. The two male Stegana triseta paralectotypes proved to belong to two unknown species closely related to Stegana acutangula, described here as Stegana dudai sp. nov. and Stegana turrialba sp. nov., and another male specimen, collected at Parque Nacional Yasuni, provinces of Napo/Orellana, Ecuador, is described as Stegana yasuni sp. nov. Additionally, we have included photomicrographs of the habitus of the type specimens as well as of some nontype specimens from Peru and Costa Rica. Based on the descriptions herein we not only clarified the status of these five species but also propose including all of them in the subgenus Orthostegana.


Introduction
During our study of the type material of Stegana (Orthostegana) acutangula (Hendel) and Stegana (Steganina) triseta (Duda), as well as other undetermined specimens of Neotropical Stegana, we identified five sibling species among them. In general, the overall morphology of these specimens was not entirely different from the majority of species of the Stegana subgenus Steganina Wheeler. However, all five of the species described/redescribed here share some special characteristics, especially regarding wing patterns and the complex male terminalia, including the possible presence of a completely membranous and mostly amorphous aedeagus. In our opinion, all of these species are best included in the subgenus Orthostegana Hendel . This is the second of a series of papers that are intended to clarify the identities of species belonging to the Neotropical Stegana (Vilela and Bächli, 2020).

Material and methods
The redescriptions of two species of Stegana, one described by Hendel and another by Duda, are based on type specimens on loan from the Naturhistorisches Museum Vienna (NMW), the Hungarian Natural History Museum, Budapest (HNHM), the Zoological Museum Berlin, Germany (ZMB) [now known as the Museum für Naturkunde, Leibniz-Institut], and on undetermined Stegana spp. on loan from the Smithsonian Institution, National Museum of Natural History, Washington D.C. (USNM). In addition, specimens are included from the former "Staatliches Museum für Tierkunde Dresden", now Senckenberg collection, Dresden (SMT) as well as from the collection of Michael von Tschirnhaus, housed as a gift in the Drosophilidae collection of the Zoological Museum at the University of Zurich (ZMUZ).
Label data attached to each type specimen are cited in full with a slash [/] indicating a line change and a double slash [//], indicating a label change. Our notes and/or interpretations are included within brackets throughout the text. Specimens loaned from USNM (USNMENT) bear a white label with a QR code printed on the backside.
Type species: Orthostegana acutangula Hendel, 1913 (monotypic). Diagnosis (modified from Zhang et al., 2012). Head setae generally thick and long, postocellar setae minute and short. Interfrontals numerous, large. Eye main axis almost vertical. Pleura with or without one upper longitudinal stripe. Tibia of middle leg basally with a posterodorsal row of 3-5 strong, erect setae, followed downwards with a row of posterodorsal smaller setae (see Figs. 2A-D in Zhang et al., 2012). Wings (see Figs. 1C-E in Zhang et al., 2012): generally dark brown, especially along the costa, almost transparent in basal 1/4 and cell m-IV, outside the posterior crossvein a roundish, fully hyaline window may be present; vein R 2+3 almost straight, slightly curved upwards just before terminating in vein C (obviously referred by the name Orthostegana); vein R 4+5 almost straight in apical half; vein M softly and more or less continuously curved upwards to vein R 4+5 ; costal section IV weak and relatively short, acrocostal (ac) index large (about 8-17 in the nine available descriptions); hb index (describing the length of the costal fringe in costal section III) large, up to 1.00. Abdominal tergites usually dark brown to black except for tergite 1+2, yellowish-brown, and basal and lateral areas paler. Outer paraphysis remarkably developed (embracing gonopore) probably acting as the surrogate intromittent sclerite together with the complex dorsal arch. Inner paraphysis proximally articulated or even fused to posterolateral region of aedeagal apodeme and distally articulated to a complex "dorsal arch". Aedeagus appears absent or, if present, could be represented by a completely membranous, amorphous or condom-shaped component.
Terminalia ♂ ( Figs. 5,6,11,12), based on Stegana acutangula lectotype #313 (Bolivia, Mapiri), Wien, and two nontype specimens #64 and #67 of Stegana acutangula (Peru, Madre de Dios, Manu). Epandrium (Figs. 5, 11)    microtrichose, except for a narrow anterior stripe and a ventral area adjacent to surstylus, posteriorly setose, bearing a conspicuous row of long, strong setae adjacent to distal margin (six ventralmost setae gradually reducing in size toward lower area), surrounded by an irregular row of smaller setae; devoid of ventral lobe. Cercus dorsally narrow, densely setose, not microtrichose; ventral lobe long, flattened, medially expanded and sharply pointed outwards, bearing a single, very thin seta, finger-shaped and curved inwards at very tip, not microtrichose, anterolaterally linked to epandrium by membranous tissue. Surstylus somewhat rectangle-shaped, double-walled, dorsodistally bearing a single, strong, terminal projection resembling a large prensiseta (but without socket) on tip of outer surface, ca. 6 long setae along distal margin, and ca. 3 thin setae on distal upper margin of inner surface, not microtrichose, not fused to epandrium. Decasternum distally square-shaped, dorsoventrally flattened, medioventrally keeled, medially incised at distal margin, bearing two lateral arms articulated to hypandrium arms. Hypandrium slightly sinuate in lateral view (Figs. 6c, 12b), as long as wide, anterior margin convex, posterior margin sinuate, medially fused to gonopods; posterior hypandrial process absent; gonopod strongly sclerotized, fused to hypandrium but projected posterad from its mediodistal margin, linked to outer wall of outer paraphysis by membranous tissue. Dorsal arch (see Bächli et al. 2004: 14) remarkably complex, connecting decasternum and hypandrium arms to inner paraphysis, divided into left and right halves (Figs. 6a,c), each two-sectioned; anterior section longitudinally half egg-shaped, weakly sclerotized, mediodistal outer surface covered with long, very thin socketed setulae, anteriorly articulated to distal region of inner paraphysis; posterior section flattened, strongly sclerotized, sharply pointed distally, laid between outer paraphysis, posteriorly articulated to anterior margin of decasternum and laterally connected to distal region of hypandrial arms; the whole sclerite probably display complex movements during the protrusion process. Aedeagus absent or, if present, could be represented by a completely membranous, amorphous component, not acting as an intromittent organ but most probably replaced by both the well-developed pair of outer paraphyses and the pair of sharply pointed anterior sections of dorsal arch. Aedeagal apodeme rod-shaped, ventrodorsally waved, distally bifid. Ventral rod fan-shaped, strongly sclerotized, anteroposteriorly flattened, laterally flanked by inner and outer paraphyses, widely articulated to median area of hypandrium between fused gonopods. Outer paraphysis (Figs. 6, 12) well developed, double-walled, distally rectangle-shaped and serrate with ca. 9 similar teeth at distal margin, medioventrally covered with ca. 13 short socketed setulae in the distal area, medially curved, strongly anteriorly sclerotized and flattened dorsoventrally but narrowed in lateral view, linked to gonopod and laterally to ventral rod by membranous tissue. Inner paraphysis laterally flattened, narrow strip-shaped, anteriorly fused to laterodistal region of aedeagal apodeme, distally articulated to setulose anterior section of dorsal arch. Ejaculatory apodeme relatively long 12a,b,d), half as long as aedeagal apodeme and unusually positioned over it, probably because of the putatively short posterior ejaculatory duct that runs from ejaculatory bulb to gonopore.
♀  Differences to male: Abdominal tergites only laterally with strong marginal setae. Front generally shorter and broader. Palpus slightly broadened. ♀ Terminalia [#77] (Fig. 16). 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 andLaštovka andMáca, 1982) horizontally positioned, somewhat rectangle-shaped in ventral view, triangle-shaped in profile view, posterior margin with a median shallow notch, and not protruding beyond hypoproct. It is devoid of peg-shaped setae and it

Distribution.
Bolivia and Peru (new record). Probably widespread in northwestern South America and perhaps in the whole Amazon Forest biome. The male specimen previously recorded from Nicaragua (Wheeler and Takada 1971: 229) proved to belong to the sibling species described below as Stegana turrialba sp. nov. The records from Panama (Canal Zone) and perhaps Colombia need to be confirmed.

Comments.
At first sight, we found a certain degree of variability among the 36 studied specimens that we suspected belonged to just one widespread species. However, further analyses of the male terminalia showed the following remarkable details. Although the external male terminalia of the Stegana acutangula (# 313) lectotype from Bolivia (Fig. 5) and the one Stegana triseta (# 317) paralectotype from Costa Rica (Figs. 40a-c) are very similar, the surface and profile shape of the distal region of the outer paraphysis differ between the two specimens. The Bolivian lectotype has a distally clear-cut square-angled outer paraphysis ornate with a serrate distal margin bearing ca. 9 teeth (Figs. 6b,d), while the Costa Rican Stegana triseta paralectotype is ornate with only ca. 3 teeth (Figs. 41a,d) and has a roundish, not square-angled, ventral tip. The latter specimen is described below as Stegana (Orthostegana) turrialba n. sp., a Central American species, so far recorded from Nicaragua (and probably from Panama and Colombia) under the binomial Stegana acutangula (misidentification).
It should be emphasized that the serrate silhouette of the distal margin of the bent, rectangle-shaped outer paraphysis is one of the most striking features of the internal male terminalia of Stegana acutangula. With a rectangle-shaped head silhouette and nine (coincidentally) equal-sized spikes, it resembles the fictional American character Bart Simpson of the animated TV series "The Simpsons Family". Stegana (Orthostegana) triseta (Duda, 1925), comb. nov. (Figs. 17-24) Oxyphortica triseta Duda, 1925: 160 (description, type material), Duda, 1927: 14, 31 (key, distribution, type material).

Comments.
The syntype material from the Budapest Museum contained four specimens (3 ♂♂ and 1 ♀), not three specimens as reported by Duda (1925:161, 1 ♂, 2 ♀♀;1927:31, 1 ♂, 2 ♀♀ in Budapest, but see Bächli, 1984:258, 2 ♀♀ in Berlin). Only one of them fully fits the description of Duda and was, therefore, selected as a lectotype. The three (2 ♂♂, 1 ♀) other specimens are herein selected as paralectotypes. The latter two males are different from the former and also between each other in several characteristics, and are described below as Stegana dudai, sp. nov., and Stegana turrialba, sp. nov. The female #316 cannot be associated with any of the three male specimens belonging to the type series. Notably, the pleuron of the female is devoid of a dark brown longitudinal stripe, which is present in the male lectotype. Previously, Brake and Bächli (2008: 300) erroneously mentioned that the Budapest Museum material was lost.   Thorax (Fig. 18c) brownish-yellow, length about 2.11 mm. h index about 0.30, dc index about 0.28, distance between apical scutellars about 85% of that of the apical to the basal one. Pleura yellowish, with a distinct dark brown longitudinal stripe along dorsal margin (Fig. 18a). Sterno index about 0.97. Wing (Fig. 20c)  Terminalia ♂ (Figs 21, 22). Epandrium (Fig. 21) distally microtrichose, bare at velum-shaped fold of anterior margin and the posteroventral area adjacent to concave margin surrounding surstyli, with a single tiara-shaped, medially positioned row of ca. 19 (8 on each side) long setae ventrally followed by irregular rows of short setae; bearing an inverted Y-shaped, sclerotized area adjacent to cercus. Cercus lower-positioned, tiny, conoid-shaped in lateral view (Fig. 21a,b), densely setose, neither microtrichose nor fused to epandrium; ventral lobes not microtrichose, strongly sclerotized and remarkably fused to one another forming a huge, rod-shaped, upwards bent, spine-shaped component (Fig. 21). Dorsal arch (connecting hypandrium arms) large, triangle-shaped. Surstylus roughly golf club-shaped in lateral view, shaft strongly sclerotized, slightly curved dorsalwards and inwards ending in a sharp tip, double-walled, outer wall lateroventrally bearing a patch of ca. 7 long, thin setae (as long and thin as cerci setae), prensisetae absent on inner margin; surstyli shaft convergent over fused cercal lobes; weakly linked to epandrium by membranous tissue. Decasternum strongly sclerotized, dorsoventrally flattened, proximally abruptly turned inwards, distally fused to ventral margin of surstyli. Dorsal arch strongly sclerotized, somewhat triangle-shaped, projected backwards sheltering aedeagus or even attached to it, distally sinuate in lateral as well in anterior view, medially carinate, medially turned rightwards, distally turned leftwards, linked to posterior hypandrium arms by membranous tissue. Hypandrium somewhat drop-shaped in anterior view (Fig. 22d), distolaterally turned dorsalwards, slightly wider than long, as long as epandrium, anterior margin convex, posterior margin concave, lateral arms strongly sclerotized, close to each other, distally hook-shaped and linked laterally to strongly developed dorsal arch; posterior hypandrial process absent; left gonopod ( Fig. 22c) weakly sclerotized, triangle-shaped, apparently linked both to hypandrium posterior margin and to left paraphysis by membranous tissue; right gonopod smaller (Fig. 22d). Aedeagus (Fig. 22b, c) membranous, somewhat tubular, covered with microtrichia which are longer and denser above gonopore, as long as aedeagal apodeme, apparently tightened linked to ventrodistal area of the strongly sclerotized, plate-like dorsal arch, probably acting as the intromittent organ together with the pair of asymmetrical outer paraphyses and rod-shaped inner paraphyses; probably linked to aedeagal apodeme by a narrow membranous tissue. Aedeagal apodeme (Fig. 22b) anteriorly expanded dorsoventrally in lateral view, distally expanded laterally in anterior view. Ventral rod strongly sclerotized anteroposteriorly flattened, bifid at tip, linked to posterior hypandrium margin by membranous tissue. Outer paraphyses strongly sclerotized, conspicuously asymmetric (Fig. 22c); right paraphysis (the longest) devoid of setae, ventromedially serrate, distally twisted and turned to the left, sharply pointed at tip, marginally smooth; left paraphysis anteriorly conspicuously expanded laterally, serrate dorsomarginally at distal half and tip. Inner paraphyses 1/2 the length of outer paraphyses, rod-shaped, flanking aedeagus, distally pointed and turned upwards, left one slightly longer than right one. Ejaculatory apodeme (Fig. 22c) weakly sclerotized, relatively short, 1/6 as long as aedeagal apodeme and unusually positioned over it, probably because of the extremely short posterior ejaculatory duct that runs from ejaculatory bulb to gonopore.
The epithet dudai is genitive and refers to the Dipterist Oswald Duda who was one of the pioneers of drosophilid taxonomy.
Comments. During dissection, the ejaculatory apodeme can sometimes be detached from the internal terminalia, which occurred with the paratype.
The epithet is a noun in apposition referring to the type locality. Terminalia . Extremely similar to that of Stegana turrialba sp. nov., except for some subtle but clear-cut non-overlapping differences mainly regarding cercus ventral lobe and surstylus (Fig. 45), as well as outer paraphysis (Figs 46-47b). Cercus ventral lobe (Fig. 45b-d) bearing a vertical row of three very thin, long setae (one single seta in S. turrialba sp. nov.). Surstylus (Fig. 45a-c) somewhat rectangle-shaped in profile view (somewhat triangle-shaped in S. turrialba sp. nov.), devoid of peg-shaped, socketed prensiseta in both species; distal margin ( Fig. 45b) shallowly concave (deeply concave in S. turrialba sp. nov.); dorsal inner corner (Fig. 45c,d) bilobulated (monolobulated in S. turrialba sp. nov.). Decasternum anterodorsal surface densely covered with long, very thin socketed setulae similar to those on outer surface of anterior section of dorsal arch (apparently only some setulae on the anterocentral region of dorsal surface in S. turrialba sp. nov.). Dorsal arch complex, roughly a quatrefoil window in posterior view (Fig. 46a), encircling posterior ejaculatory duct and/or gonopore anteriorly (as in S. turrialba sp. nov.). Outer paraphysis proximally twice as wide as distally in profile view (Fig. 46b) (distally widened and projected distal wards as a lobule in S. turrialba sp. nov.); outer surface ( Fig. 46b) bare (dorsodistally covered with ca. 40 tiny scales in S. turrialba sp. nov.).
Female. Unknown. Distribution. So far only known from the holotype collected in the Amazonian region of Ecuador. This is the first record of a Stegana species occurring in Ecuador (see Brake and Bächli, 2008) and in the Yasuní National Park (see Acurio and Rafael, 2009).

Etymology.
The epithet is a noun in apposition referring to the type locality.

Discussion
In comparison with the current diagnosis of the subgenus Oxyphortica (Wang et al., 2017), the external characteristics of species of the subgenera Orthostegana and Oxyphortica are extremely similar and in some cases overlap. In species of Oxyphortica, the M vein of the wing is less curved, but this trait provides little definitive evidence because of intra-and interspecific variations. Herein, we compared the wing vein characteristics of all 40 known Oxyphortica species and found that costal section IV is much longer, thus reducing the ac index to about 4-7. It should be pointed out that costal section IV is weak and usually not flattened in this subgenus, which could lead to errors in the ac index measurement. Additionally, the number of erected posterodorsal setae on the middle tibia is variable but does not discriminate between the two subgenera, and a row of posterodorsal setae on the middle tibia, with a few of the upper ones being stout and erect, has been observed in a variety of Stegana species belonging to other subgenera as well.  The descriptions and illustrations of the six Asian species of Orthostegana reveal that all exhibit a distinct, sclerotized aedeagus (Sidorenko, 1990;Chen and Wang, 2004;Zhang et al. 2012;Li et al. 2013), a common feature of the Oxyphortica subgenus (for further details, see Wang et al., 2017). On the other hand, in Stegana acutangula, type species of the subgenus Orthostegana, this structure is amorphous (membranous).
Since the external characteristics of all 40 species of the subgenus Oxyphortica were recorded in Asia and many details, including a completely dissimilarity shaped aedeagus, overlap with these six Asian species of the Orthostegana subgenus. Thus, we propose that the Asian Orthostegana species should be included in Oxyphortica, consequently making Orthostegana an endemic American subgenus.
Previously, Bächli et al. (2004: 14) proposed that the structure designated as the "dorsal arch" of the hypandrium in Steganinae probably originated from the gonocoxite. In the present study, we compared the ribbon-shaped process described by Bächli et al. 2004: 203, Figs 499, 500) that is responsible for the hypandrium arm-inner paraphysis connection in species of obscura group of Drosophila, to the "dorsal arch" described in the five Stegana sibling species (Figs. 6a-c, 22b, 30a,c, 35a,b, 46c,d) cited above. We found that the inner paraphysis of the latter five species clearly articulates distally with the "dorsal arch", and proximally to both the hypandrium arm and distal end of aedeagal apodeme. The similar role of the "ribbon-shaped process" of the obscura group of Drosophila and the complex two-sectioned "dorsal arch" of the five species of Stegana analyzed above, indicates that both structures must be homologous and probably originated from the gonostylus, the distal arm of the primitively two-segmented gonopod (McAlpine 1981: 45), together with the distal region of the decasternum, and not the gonocoxite as previously proposed by Bächli et al. 2004. Moreover, in the species of the subgenus Drosophila, the single pair of paraphyses connects the distal end of aedeagal apodeme to the gonopod, which most likely originated from the basal arm (gonocoxite) of the primitively two-segmented gonopod and the apparently absent pair of primitive inner paraphyses is probably fused anterodorsally to the aedeagus.