Drosophila thoracis Williston 1896
Creators: name: Grimaldi, David A.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Drosophilidae
Drosophila
Drosophila thoracis

description: Drosophila thoracis Williston, 1896: 411.
DIAGNOSIS: Relatively small fly with contrasting color: top of head and thorax dark brown; most of pleura and all of legs light cream color, thin dark brown band just below notopleural suture; abdomen mostly black-brown, with pattern as described below. Basal flagellomere with long setulae; arista with 1–2 ventral, 4 long dorsal branches; anterior dorsocentral seta small, only ca. 0.4× length of posterior dorsocentral. Face relatively deep (FD/FW 1.25), cheek shallow (CD/ED 0.10). Wing mostly clear with small, faint infuscate area below apex of Sc vein; vein R 2+3 short (C-index 1.27). Anterior dorsocentral seta short (DC-index 0.46). Male: Cercus with fingerlike ventromedial lobe; surstylus broad, rounded; aedeagus virtually straight, apex almost round in ventral view, constriction between bulbous apex and neck. Female: Oviscapt margin entire, no differentiation of pegs at apex.
DESCRIPTION: Coloration: Little to no sexual dimorphism. Head: Frons with anterior portion light fuscous; posterior portion dark blackish brown. Frontal vittae matte, finely striate; ocellar triangle and fronto-orbital plates slightly darker, shiny; area bounded by ocelli dark, blackish brown. Face and carina light, oral margin, vibrissal angle and anterior portion of cheek fuscous brown; posterior portion of cheek light, cream colored. Antenna with scape light, pedicel and basal flagellomere light brown; arista dark with minute basal articles cream colored. Eye dark red. Clypeus light brown (same as oral margin), palp and rest of proboscis light (creamy). Thorax: Scutum and scutellum dark brown, scutum with faint, diffuse pair light paramedian stripes on anterior third. Pleura: Thin, dark brown stripe just below notopleural suture, extending from anterior edge of thorax to wing base; rest of pleura creamy white. Wing mostly hyaline, with small, faint infuscate area below apex of Sc vein; halter stem slightly infuscate, knob lighter. Legs entirely cream colored. Abdomen: Mostly blackish to black-brown, shiny; with light median stripe on tergites 1–3; tergite 4 with light transverse band on anterior half, small, light median triangle on posterior margin; tergites 5, 6 entirely or virtually all dark.
Head: Antenna: Scape bare; pedicel with setulae, 2 slightly larger setae; basal flagellomere of moderate length (apex not reaching to level of oral margin), with long, light setulae (especially on anterior edge and apical half); arista with 1 ventral, 4 long dorsal branches, plus terminal fork, ventral branch between apical fork and d-4. Eye unevenly egg shaped in lateral view, posteroventral margin flattened; interfacetal setulae short, dense. Face: Width and depth moderate, slightly concave; carina small, narrow, on upper 2/3 of face. Vibrissae: 1 pair, subvibrissal setulae much smaller. Cheek shallow. Frons: Relatively flat; fronto-orbital plates shiny, narrow; frontal vittae finely striate, little differentiation between its edges and those of ocellar triangle. Frontoorbital setae: proclinate slightly longer than posterior reclinate; anterior reclinate tiny (ca. 0.3× size of proclinate), midway between ipsilateral orbitals; posterior reclinate much closer to proclinate than to verticals; reclinates and inner vertical in a line, proclinate slightly medial to this tangent. Ocellar seta extending to level of proclinate; postocellar setae ca. 0.5× length of ocellars, tips crossed. Inner vertical setae short, inclinate; outer vertical setae moderately lateroclinate. Proboscis short, at rest entirely withdrawn into oral cavity; labellum broad when opened.
Head measurements (N = 4): CD/ED 0.10 (0.08–0.14), ED/EW 1.24 (1.22–1.27), FD/FW 1.25 (1.15–1.33), FL/LFW 0.97 (0.93–1.07), HW/ HD 1.48 (1.41–1.62), Ocellar S-index 1.28 (1.25– 1.30), OR1/OR3 1.24 (1.12–1.33), OR2/OR1 0.42 (0.37–0.50), VT-index 0.92 (0.76–1.05).
Thorax: Setation: Acrostichal setae in 6 rows; anterior dorsocentral seta small, fine, ca. 0.4× length of posterior dorsocentral, latter closer to anterior dorsocentral than to scutellar margin. Anterior scutellar setae small (ca. 0.5× length posterior scutellars), parallel; posterior scutellars parallel to slightly convergent. Postpronotal lobe with 2 setae; 3 notopleurals, all equal in size; 2 supra-alar setae (posterior one longest); 2 postalar setae (anterior one very long). Katepisternum with 2 setae, anterior one short, ca. 0.4× length of posterior katepisternal. Legs: Forefemur with ventral row 4 erect, short setae, 1 lateral seta (lengths shorter than width of femur), mid- and hind femora without larger setae; male foretarsus with ca. 10 very fine, short, erect setulae on dorsal surface. Midtibia with stout ventroapical seta; hind tibia with fine preapical dorsal seta.
Thorax and wing measurements (N = 4): ThL 0.79 mm (0.71–0.91), DC-index 0.46 (0.39–0.56), S-index 0.39 (0.36–0.45), 4-V index 2.41 (2.23– 2.57), 5-X index 2.69 (2.53–2.72), C-index 1.27 (1.17–1.44), hb-index 1.64 (1.54–1.85), ThL/WL 0.46 (0.44–0.49), WL/WW 2.27 (2.22–2.35).
Abdomen: Relatively short, broad, somewhat dorsoventrally flattened. Male Terminalia: Epandrium broadly arched, with microtrichia overall (including ventral lobe), row of 8–10 setae on lateral surface, none dorsally; ventral lobe of epandrium relatively short, extending slightly past lower level of surstylus. Cercus not connected to epandrium, with fingerlike ventromedial lobe; broad, short ventrolateral lobe (both lobes with very fine setulae). Surstylus broad, rounded in full lateral view, with row 5–8 peg prensisetae lateral to some 10–12 setiform prensisetae on mesal and ventral margins; no microtrichia. Hypandrium moderately short and broad, anterior margin flat; paraphysis small, with pair of minute setulae mesally, stout seta at apex. In lateral view aedeagus slightly curved, aedeagal apodeme broad and keel shaped; aedeagus ca. 2× length of aedeagal apodeme; in ventral view tip of aedeagus subcircular to nearly circular, constriction between this portion and neck; dorsal surface of neck and bulbous apex sparsely, finely pimplate. Aedeagal apodeme extended well beyond anterior margin of hypandrium. Female Terminalia: Oviscapt with apical margin entire, no differentiation of pegs; marginal row of ca. 13 pegs, decreased in size anteriad; oviprovector well developed, scales coarse on posterior surface. Spermatheca dome shaped, with small terminal umbilicus; introvert short, ca. 0.45× length of capsule; exterior of capsule with 3 faint ribs at base.
TYPES: Two cotypes, from which a lectotype was designated here. “Windward Is[lands], St. Vincent, BWI [British West Indies], H.H. Smith/ W. Indies/ Drosophila thoracis ” (handwritten). In the Natural History Museum, London (not dissected).
OTHER SPECIMENS EXAMINED: USA: Arkansas: Logan Co., Magazine Mtn., 2750 ft., D. Grimaldi, VII/16/92, collected at 2200 ft. from oak sap flux, 1♀ (AMNH). Florida: Orlando, June 26, 1953, M.R. Wheeler, on fungus, 4♂, 6♀ (1 of each dissected, nos. 30, 31 respectively) (AMNH). 14 mi. E. Orlando, cypress swamp area, [field notebook no.] 2314.8, VI/26–27/53, W. B. Heed, M.R. Wheeler, 3♂, 1♀ (AMNH). Alachua Co., Gainesville, Possum Creek Pres. 19/ VII/2007, on fungus, S. Bybee, 1♀, 2♂ (1 dissected, no.14). Louisiana: Chicot S. Pk. [State Park] nr. Ville Platte, Sept. 1954, M. Wheeler, 4♂ (1 dissected, no. 29), 2♀ (AMNH).
COMMENTS: According to Wheeler (1981) this species occurs in the West Indies to the southeastern United States. Actually, it has an even wider distribution, perhaps the widest distribution of all New World Hirtodrosophila save H. pictiventris. Based on my dissection of dozens of male specimens throughout the range (including from St. Vincent, the type locality), the male genitalia are remarkably uniform throughout the range. Hirtodrosophila thoracis occurs in the north from Louisiana and Florida, throughout Central America and the Caribbean, south to central Brazil and Ecuador. Neotropical distribution records will be provided in detail elsewhere, along with the description of several new Neotropical species superficially similar to thoracis.
description: Published as part of Grimaldi, David A., 2018, Hirtodrosophila Of North America (Diptera: Drosophilidae), pp. 1 in Bulletin of the American Museum of Natural History 2018 (421) on page 1, DOI: 10.1206/0003-0090-421.1.1, http://zenodo.org/record/10687866