Ditomyia nana Fitzgerald, 2020

Fitzgerald, Scott J., 2020, Revision of the Nearctic species of Ditomyia Winnertz and a new species from the Neotropical Region (Diptera: Ditomyiidae), Zootaxa 4859 (2), pp. 239-262 : 253-256

Ditomyia nana Fitzgerald n. sp.

Figs. 38–46

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Type Material. Holotype: Male, point-pinned ( CNCI), GUATEMALA: Guatemala, Puerta Parada , 1840 m alt., 5–12 V 2018, J.C. Schuster . Paratypes: Same as holotype except: 1850 m, Bosque cipres, 19–26 Oct 2013, 2 females (1 SFC, 1 UVGC) .

Diagnosis. Ditomyia nana can be distinguished from other New World Ditomyia by the following combination of characters: Small size (wing ca. 3.25 mm), wings hyaline, r-m crossvein absent, with Rs, stem of M 1+2, and bm-cu crossvein meeting in a point ( Fig. 39 ), vertex of head distinctly bulging and elevated ( Figs. 40–41 ), maxillary palpus two-segmented, male terminalia as Figs. 42–45 , female terminalia as Fig. 46 with ultimate segment of cerci broadly rounded.

Remarks. Ditomyia has been considered a strictly Holarctic group and the several “Neotropical Ditomyia ” species previously described have ultimately been reassigned to other genera (e.g. Nervijuncta conjuncta ( Freeman, 1951) , Australosymmerus mexicanus ( Giglio-Tos, 1890) and A. zonatus ( Giglio-Tos, 1890) ; Monroe 1974, Papavero 1977). However, after comparison with characters of all other ditomyiid genera, Ditomyia nana n. sp. is tentatively placed in the genus Ditomyia and compared to the similar genera Nervijuncta and Asioditomyia (see “Discussion”).

Etymology. The specific epithet nana is feminine of the Latin “nanus” (dwarf) for the small size of this species.

Description. Male ( Fig. 38 ). Mostly dark brown. Body length (including antennae) [ca. 4.0] mm. Head. Light brown with short black setae, areas around ocelli blackish. Three dorsomedial ocelli, arranged in a transverse line, median ocellus much smaller. Vertex distinctly bulging. Frontal suture (running between compound eyes anterior to ocelli) ( Figs. 40–41 ) present. Compound eye oval with fine ommatrichia, widely separated dorsomedially, not emarginated at antennal base. Maxillary palps brown to pale yellow, two-segmented (though it is possible a minute basal segment is present, but can’t be seen) with basal segment stout, humped, and apical segment minute. Fifteen barrel-shaped flagellomeres, ultimate flagellomere minute, oval. Flagellomeres light brown with short, black, stiff, setae and pale pubescence. Pedicel light brown and scape slightly more pale yellow. Base of antennal setae marked with a black spot. Thorax. Pale yellow with light brown to brown markings on pleura and three broad, light brown, longitudinal stripes on scutum; lateral stripes shorter, truncated anteriorly and median stripe tapering posteriorly and not reaching scutellum. Scutum with long dark setae laterally and in dorsocentral rows. Scutellum brown, without setae. Thoracic pleura mostly light brown, bare. Legs. Fore tibia, and right hind leg missing. Light brown becoming darker distally. Legs with dense appressed microtrichia. A row of sparse black posterior setae running nearly full length of hind tibia. Hind basitarsus missing. Tibial spurs?:2:2 (1:2: 2 in female). Wing ( Fig. 39 ). [ca. 3.25] mm. Hyaline with dense microtrichia throughout and macrotrichia present, but mostly concentrated near the wing tip. Veins brown, anterior veins darker. C ending near wing tip, ending about one-third the distance between R 4+5 and M 1. Sc short, ending free, abruptly near base of wing, followed by long, faint, distal portion (crease), ending free near level of base of Rs. Base of Rs and stem of radial fork nearly subequal in length. R 2+3 long, base basal to level of medial fork. R-m absent, with Rs, M 1+2, and bm-cu meeting in a point. Stem and fork of M weakly pigmented. CuP reaching wing edge. Abdomen. Brown without bands. Terminalia ( Figs. 42–45 ). Tergite nine greatly reduced in size, roughly rectangular, the posterior edge with a small median hump. Cerci, broad, fleshy, flap-like. Gonocoxites fused dorsally with a pair of broad subtle lobes on posterior margin. Gonocoxites also fused (with hypandrium) ventrally, with posterior margin developed into a pair of broad, shining, asetose, apically truncate lobes (possibly homologous with hypandrial lobes of other species; otherwise hypandrium indistinct). Gonostylus elongate blade-like, tapering apically, inner edge, with an elongate weakly serpentine, black, sclerotized, ribbon that is minutely serrated when viewed at higher magnification ( Fig. 43 ). Paramere short, tower-like.

Female. In most aspects essentially as in male, except as follows. Second segment of maxillary palpus even smaller than in male (and in one female ultimate segment apparently absent, but maybe just broken off?). Tibial spurs 1:2:2. Cerci brown, two-segmented, basal segment elongate, apical segment short oval ( Fig. 46 ). Sternite eight longitudinally divided medially.

Distribution. Guatemala.

Figures

FIGURES 38–39. D. nana, n. sp., holotype male. 38. Habitus, lateral. 39. Wing. Scale bars = ca. 1.0 mm.

FIGURES 40–41. D. nana n. sp., head. 40. Male, holotype, anterior view. 41. Female, paratype, lateral view. Scale bars = ca. 0.25 mm. Abbreviations: fs, frontal suture; lo, lateral ocellus; mo, median ocellus; mp1, maxillary palpus one; mp2, maxillary palpus two; v, vertex.

FIGURES 42–46. D. nana n. sp., terminalia. 42–45. Male, holotype. 42. Lateral. 43. Close-up of serrated edge on gonostylus, ventrolateral. 44. Dorsal. 45. Ventral. 46. Female, paratype, lateral. Scale bars = ca. 0.25 mm, except Fig. 43 scale bar = ca. 0.05 mm. Abbreviations: c, cerci; c1, cercus one; c2, cercus two; gc, gonocoxite; gs, gonostylus; h, hypandrium; hl, hypandrial lobe; p, paramere; s8, sternite eight; t9, tergite nine.