Sierramyia, Kerr, 2010

Kerr, Peter H., 2010, 2592, Zootaxa 2592, pp. 1-133 : 88-89

Genus Sierramyia , new genus

Figs. 59, 131, 142.

Sierramyia Type species Neorhagio caligatus Santos 2006: 51 , by present designation.

Diagnosis. Characters that I regard as autapomorphic for the genus Sierramyia include the weakly developed or absent anal lobe of the wing, so that the alular incision is rounded and open broadly or absent; the upper calypter reduced; and the proepimeron bare. The swollen hypandrium, which is expanded anteriorly, may also be autapomorphic. The scarcity of examplars for this genus makes it difficult to assert more autapomorphies at the species group level. However, the Sierramyia species are very distinctive and their monophyly seems likely.

Species of Sierramyia are small to mid-sized flies (approximately 5.6 mm) that are slight of build and are similar to Rhagio in several aspects; laterotergite setose, tibial spur formula 0:2:2, antenna with round first flagellomere bearing terminal arista; arista bare; wings often infuscate or with markings; M 3 present. Both sexes are dichoptic. They may be distinguished immediately from Rhagio and all other genera by the unusually modified wing that is weakly developed along its posterior margin, including a very reduced upper calypter. Additionally, Sierramyia species may be distinguished from all Rhagio species and the related genus Desmomyia by having a bare proepimeron and by having setulae on at least the dorsal surface of R 5 and on the ventral surface of R 2+3 and R 4. Sierramyia species differ from Chrysopilus and related chrysopiline genera such as Schizella and Stylospania by having two hind tibial spurs and by the absence of scale-like thoracic setae.

Description. Head. Clypeus bulbous. Scape approximately same size as or shorter than pedicel. First flagellomere oval in cross section, lightly compressed laterally; enlarged basally, bearing fused, bare aristalike extension. Eyes inconspicuously setulose, dichoptic. Palpus one-segmented. Mandibles absent.

Thorax. Mesonotum without vittae. Dorsocentral bristles absent, all dorsal setae of equal length. Anepisternum setulose on dorsal margin only. Laterotergite setose, on ventral half (katatergite) only. Postspiracular scale absent. Proscutellum shallowly present. Subscutellum not enlarged nor lengthened; inconspicuous. Wing membrane darkly infuscate, with hyaline markings, or entirely hyaline; with or without pterostigma. Lower calypter reduced. Upper calypter underdeveloped, with narrow curvature, width more than twice length. Costa reaching approximately to wing tip. Humeral crossvein well developed, Sc-r crossvein weakly developed, positioned distal to h by a little more than length of h. Dorsal side of R 1 setulose, ventral side of R 1 bare. R 2+3 sinuous, apical third of R 2+3 ultimately bends anteriorly slightly, toward wing tip; about same length as R 5; with setulae on both sides of membrane. Base of R 4 –R 5 fork proximal of distal end of cell dm. R 4 at base relaxed, not strongly curved, nearly straight apically; dorsal side bare, ventral side with setulae. R 4 and R 5 contain wing tip. R 5 clearly longer than R 4+5 (r-m to R 4 origin); dorsal side setulose, ventral side bare. M 3 present. Cell m 3 parallel-sided at margin. Origin of CuA 1 at cell bm. Length of CuA 2 v. posterior vein of cell bm about same as 1/2 length of posterior vein of cell bm. Alula reduced. Anal lobe reduced. Cell cu p open. Halter knob between 1/3–1/2 length of stem. Tibial spur formula 0:2:2. Hind coxal tubercle absent. Hind tibia without ventro-apical swelling.

Abdomen. Male terminalia with epandrium simple, not containing hypandrium ventrally. Epandrium subcircular, wider than long, modestly curved anteriorly. Tergite 10 absent. Hypoproct rounded posteriorly. Hypoproct flattened, distinct from sclerites above cerci; tomentose, without setae. Cerci partially displaced from one another, separation distance approximately half width of single cercus. Hypandrium separated from gonocoxites by complete suture, expanded anteriorly. Gonocoxite with sinuous dorsal ridge, leading to gonocoxal apodeme. Gonocoxal apodemes long enough to reach anterior margin of hypandrium. Sperm sac bulbous, without paired swellings ventrally. Lateral ejaculatory processes present, integrated into sperm sac membrane. Ejaculatory apodeme long, reaching beyond anterior margin of hypandrium; laterally compressed. Aedeagal tines absent. Endoaedeagal process present, short. Female abdominal segments 5–10 evenly tapered from segments 1–4; tergite 7 much longer than wide; intersegmental membrane between segments 7 and 8 especially long; sternite 8 longer than wide. Female terminalia with three spermathecae. Spermathecal ducts longer than five times length of sternite 9, but not so long as to be difficult to measure. Spermathecal duct accessory glands not present. Ejection apparatus of spermathecal ducts lightly sclerotized, thickened, with ringed surface furrows. Spermathecal duct junction thickened. Common spermathecal duct thickened; short, shorter than longest diameter of genital chamber. Genital chamber teardrop shaped, moderately sized. Accessory gland posterior to genital chamber inconspicuous, easily overlooked even after staining. Sternite 9 anterior end broadly pointed; posterior end with broad lateral extensions, free, held in horizontal plane. Tergite 10 length approximately as long as half measured width, or longer. Sternite 10 entire, pentagonal, pointed posteriorly; posterior half below first cercal segment. Cercus two-segmented. First segment of cercus not elongate, without ventral process. Ventral lobes of first segment of cercus curve ventrally towards one another to form ring, visible in posterior perspective (curving slightly ventrally; not obvious). Basal cercal segment adjacent dorsally. Second cercal segment not elongated. Cercus with or without apical sensory pits.

Larva. Unknown.

Biology. All Sierramyia species are endemic to mountainous areas (at 1500 masl or greater) in Mexico.

Literature. Nagatomi (1982 a, 1984) illustrates wing, antenna, and male genitalia of two undescribed species belonging to this genus. Santos (2006) described the only two species in the genus, providing illustrations of the head, antenna, wing, male genitalia, and female genitalia for each species; it is possible that one or both of these were previously studied by Nagatomi. It is keyed to the genus level as “Undescribed Genus A” by Kerr (2009).

Notes. Nagatomi (1982a) recognized that Neorhagio Lindner was likely a junior synonym of Atherimorpha White , but placed several undescribed specimens from Mexico in what he referred to as ‘ Neorhagio ’. He gave no explanation why these specimens belong to Neorhagio Lindner. As a matter of convenience, Santos (2006) elected to retain this designation for two new species, which he described. Judging from the photos, illustrations, and diagnosis given by Nagatomi (1982a) and Santos (2006), the undescribed species of ‘ Neorhagio ’ sensu Nagatomi and the species described by Santos (2006) are clearly not members of Atherimorpha . The genus Sierramyia gen. nov. is erected for these species. I was able to examine a female of what appears to be the same species that was examined by Nagatomi (1982a) and referred to as ‘ Neorhagio ’ sp. A.

Santos (2006) indicates the presence of aedeagal tines in both S. caligatus and S. nagatomii . I have not been able to inspect male Sierramyia specimens, but I believe Santos’ interpretation of these structures is in error. These small, often lightly sclerotized structures are also easily observed in most species of Rhagio , but they are clearly associated with the sperm sac and are not homologous with aedeagal tines observed in Arthroceras , Bolbomyia , Athericidae , and Tabanidae .