Drosophila thurstoni, Grimaldi, 2016

Grimaldi, David A., 2016, Revision of the Drosophila bromeliae Species Group (Diptera: Drosophilidae): Central American, Caribbean, and Andean Species, American Museum Novitates 2016 (3859), pp. 1-56 : 34-36

Drosophila thurstoni , new species

Figures 5B ; 16A–C

DIAGNOSIS: A smaller (thorax length ca. 0.90 mm), light brown to deep ochraceous-yellow species, prescutellars approximately 0.3× length of posterior dorsocentrals, lateral pairs barely differentiated; postocellar setae slightly convergent to parallel (vs. strongly convergent or even with tips crossing); aedeagus long (length 11.0× the width), strongly arched in lateral view (aedeagal angle 114°); distiphallus similar to that of bromeliae , except with much narrower apex in full ventral view; surstylus with 12 slender prensisetae, no sclerotized ventral setae; hypandrium trapezoidal.

DESCRIPTION: Male: Head: Frons light brown, pollinose on fronto-orbital plates and ocellar triangle, frontal vitta golden, shiny, finely striate; frontal index 0.96, top to bottom width ratio 1.38. Ocellar triangle slightly raised above rest of frontal surface, dark brown between ocelli, anterior corner of triangle reaching ca. 0.6× length of front. Orbital setae dark brown with bronze highlights (not black), or1:or3 ratio 0.93, or2:or1 ratio 0.40, postocellar setae 0.48× and ocellar setae 0.76× frontal length, postocellar setae slightly convergent to parallel; vt index 1.05. Vibrissal index 0.60. Face same color as ocellar triangle. Carina well developed, frontal edge flattened, with slight sulcus, greatest width of frontal edge ca. 0.6× the width of pedicel. Cheek index about 0.10. Eye index 1.43. Occiput light brown. Basal antennomeres same color as face; arista with 3 dorsal and 2 ventral branches, plus large terminal fork. Proboscis light brown; palpus slightly lighter, with one apical and one subapical setae.

Thorax length 0.89 mm. Scutum light brown, pollinose; 6 rows of acrostichal setae. One large pair of prescutellar setae, lengths about 0.33× that of posterior dorsocentral setae; setae lateral to prescutellars slightly larger than acrostichals; h index 0.85. Transverse distance of dorsocentral setae 3.33× that of longitudinal distance. Scutellum same color as scutum, pollinose; basal scutellars convergent, apical scutellars crossing at tips; scutellar seta index 0.92. Pleura slightly lighter than scutum, less pollinose, sterno index 0.74. Halter stem light, bulb slightly darker than pleura. Legs lighter than pleura.

Wing hyaline, veins yellow-tan, length 1.78 mm, length to width ratio 2.22. Indices: C, 2.20; ac, 2.25; hb, 0.60, 4-C, 1.04; 4V, 1.74; 5x, 1.41; M, 0.56. Wing tip rounded, vein R 2+3 virtually straight; section of C between h and Sc breaks with ca. 10 thicker spinules.

Abdomen light brown, pollinose; posterior margin of tergites without noticeable dark, diffuse markings.

Male terminalia (fig. 16A, B). Epandrium with microtrichia, lacking setae on dorsal surface; ventral lobe apically rounded, without microtrichia, having ca. 5 setae. Cerci with microtrichia, laterally connected to epandrium. Surstylus with extensive microtrichia on outer (lateral) surface, with inner marginal row of 12 long peglike prensisetae (vs. 7–9, as in bromeliae ), about 6 other, finer setae (none sclerotized). Subepandrial sclerite (not examined). Hypandrium trapezoidal, length 0.89× the greatest width, lateral margins straight (not convex). Gonopods fused to hypandrium; apical seta fine, minute. Aedeagus fused to aedeagal apodeme, strongly and evenly arched in lateral view, length 11.0× the width, aedeagal angle 114°; distiphallus with very narrowed tip in full ventral view; aedeagal apodeme short, keellike.

Female: General morphology similar to males. Measurements: Thorax length 0.94; Frontal top to bottom width ratio 1.41. or1:or3 ratio 0.93, or2:or1 ratio 0.66, lengths of postocellar setae 0.50× and ocellar setae 0.71× that of frontal length, vt index 1.00. Vibrissal index 0.56. Cheek index about 0.08. Eye index 1.41. Lengths of prescutellar setae 0.48× that posterior dorsocentral setae; h index 0.94. Transverse distance of dorsocentral setae 2.61× the longitudinal distance. Scutellar seta index (not measurable), sterno index 0.75. Wing length 1.81 mm, length to width ratio 2.26. Wing indices: C, 2.02; ac, 2.66; hb, 0.60; 4-C, 1.23; 4v 2.05; 5x 1.86; M, 0.71.

Female terminalia: Valves of oviscapt of moderate length, length 2.5× greatest width, ca. 280–300 µm long, tip slightly acute (not fully rounded) in lateral view; valves with 14–16 marginal oviscapt pegs. Spermatheca short, cup shaped, height approximately equal to width; basal introvert extending to ca. 0.7× the length of capsule.

TYPE: Holotype, ♂: “ JAMAICA B.W.I. [ British West Indies , printed]/ Hardware Gap [handwritten]/ W.B. Heed, M Wasserman July 1958 [printed],” dissected by D.A.G. ( DBG 34 ), stored in a glass microvial on same pin as specimen. In AMNH.

OTHER SPECIMENS: Paratype female: “ Jamaica B.W.I. [printed]/ Falmouth July 1958 [printed]/ M.W. Wasserman W.B. Heed [printed],” dissected by D.A.G. ( DBG 35 ), genitalia in glass microvial on same pin as specimen . Paratype female: “ Jamaica B.W.I. [printed]/ Hermitage Reservoir [printed]/ W.B. Heed M.W. Wasserman July 1958 [printed],” genitalia dissected by D.A.G. ( DBG 17 ), in glass microvial on same pin as specimen. In AMNH .

ETYMOLOGY: Patronym for Steve Thurston, Senior Scientific Assistant and graphic artist in the Division of Invertebrate Zoology at the AMNH, in recognition of his many years of superb skill and artistry.

COMMENTS: This species is distinguished from the widespread Drosophila bromeliae by the slightly smaller body size; light brown, pollinose body; and by the male genitalia: the surstylus dentition (12, vs. 7–9 prensisetae), distiphallus shape, and especially the aedeagal length (ca. 0.31 mm, vs. 0.22 in bromeliae ). When corrected for body size (using thorax length as a proxy), the aedeagal length of thurstoni is 33% longer than in bromeliae . Female terminalia are nearly identical, although the oviscapt pegs in thurstoni are slightly thicker and stouter than in the type of bromeliae .

Figures

FIG. 5. Wings of exemplar species in the bromeliae group. A. Drosophila bromeliae Sturtevant (DBG 43: Ecuador). B. D. thurstoni, n. sp. (DBG 35). C. D. penispina, n. sp. (DBG 21). Arrows point to distinctive features: B, to slightly pointed wing tip, short crossvein dm-cu; C, to slightly sinuous vein R2+3. To the same scale.

FIG. 16. Male genitalia of three species in the bromeliae group. A–C. Drosophila thurstoni, n. sp. (DBG 34). D, E. Species indet. (DBG 40: “Panama: Darién Province: El Real XI-29-963 Sarah B. Pipkin”). F, G. Species indet. (DBG 53: “Ecuador: Loja, 45 km SSE Portovelo, Rio Yaguachi, 080 m, 4 November, 1987/R. Davidson, J. Rawlins, C. Young, riparian scrub”).