Ditomyia elongata 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 : 240-243

Ditomyia elongata Fitzgerald n. sp.

Figs. 1 , 7–10 , 47 (Map)

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Type Material. Holotype: Female ( Fig. 7 ). USA: WASHINGTON: Mt. Rainier, Ramparts , 1 August 1922, A.L. Melander, ( USNM).

Diagnosis. Ditomyia elongata can be distinguished from other Nearctic Ditomyia by the following combination of characters: Wings hyaline with macrotrichia unevenly distributed, basal third of wing with large bare areas (cell br+bm mostly bare) ( Fig. 1 ); antennal flagellomeres light grey-brown, contrasting with pale yellow scape and pedicel; scutum pale yellow with light brown stripes ( Fig. 7 ); female terminalia as Figs. 8–10 with the ultimate segment of the cerci in lateral view relatively narrow and gradually tapered to a rounded point apically ( Fig. 10 ); female fore tibia ~1.5 times as long as fore basitarsus ( Fig. 7 ).

Remarks. While the author would generally argue that it is not advisable to describe a new species only from the female sex (because species concepts in this family rely heavily on the male terminalia), Ditomyia is so speciespoor that associating the male at a later date with the female described here should not be problematic. Particularly since there are a number of non-sexual characters that one would expect to find in the unknown male that will be distinctive (e.g. unevenly distributed macrotrichia in combination with hyaline wings and the base of R 2+3 much closer to r-m than to medial fork). Additionally, the only other species known from the western Nearctic is known from both sexes.

The type locality on Mount Rainier known as “The Ramparts” is a forested ridge that is the remnant of an ancient lava flow which originated at the summit of Mount Rainier and is known for its areas of old-growth forest (https://www.nps.gov/mora/planyourvisit/rampart-ridge-trail.htm).

Etymology. The specific epithet elongata is feminine of the Latin “elongatus” (long, prolonged) for the more elongate foreleg of this species (in comparison to the other western Nearctic species D. sohnsi ).

Description. Female ( Fig. 7 ). Entirely pale yellow with darker areas becoming light brown. Head. Mostly light brown with sparse brown setae. Three dorsomedial ocelli, arranged in a transverse line, median ocellus much smaller. Compound eye oval with fine fairly dense ommatrichia, widely separated dorsomedially, very slightly emarginated anteromedially at antennal base. Maxillary palps light brownish-grey, three to four-segmented (dif- ficult to discern). Fifteen flagellomeres, most longer than broad with basal segments most elongate, ultimate flagellomere minute, oval. Flagellomeres greyish-brown with short, black, stiff, setae and pale pubescence. Pedicel and scape pale yellow, contrasting in color to flagellomeres. Base of antennal setae not distinctly marked with a black spot. Thorax. Pale yellow with light brown markings on pleura and three broad longitudinal stripes on scutum (lateral stripes shorter, truncated anteriorly, median stripe appears slightly medially longitudinally subdivided by a very narrow pale yellow line). Scutum setose, perhaps more densely so in dorsocentral rows, setae light brown, scutellum with four seta restricted to posterior edge (two posterolateral pairs of setae). Thoracic pleura bare. Legs. Coxae and left fore leg pale yellow (remainder of legs missing). Leg with dense appressed microtrichia (except on underside of femur), without distinct macrotrichia. Fore basitarsus slender, elongate, parallel-sided; fore tibia ~1.5 times as long as fore basitarsus ( Fig. 7 ). Wing ( Fig. 1 ). [ca. 6.0] mm. Hyaline with dense micro- and macrotrichia; macrotrichia unevenly distributed with basal third of wing mostly bare. Veins pale yellow. C ending near wing tip just beyond R 4+5. Base of Sc strongly pigmented, pigmented portion ending abruptly near base of wing, followed by long, faint, distal portion (a crease), ending free near level of base of Rs. Base of Rs slightly longer than stem of radial fork beyond r-m. R 2+3 long, base much closer to r-m than to level of medial fork. R-m very short, vertical. Base of stem of M 1+2 weak. CuP reaching wing edge. Stem of M slightly shorter than M 2. Abdomen. Pale yellow without distinct bands. Terminalia ( Figs. 8–10 ). Tergite nine apparently absent, tergite ten greatly reduced to a slender transverse band. Cerci, pale yellow, two-segmented with apical segment comparatively narrow, fleshy, flap-like, in lateral view gradually tapered to a rounded point apically ( Fig. 10 ). Sternite eight medially deeply cleft in ventral view with posterior edge serrate in lateral view.

Distribution ( Fig. 47 ). Presently known only from Mt. Rainier Washington.

Figures

FIGURES 1–4. Wings. 1. D. elongata n. sp., holotype female. 2. D. euzona, male. 3. D. potomaca, female. 4. D. sohnsi n. sp., holotype male. Scale bars = ca. 1.0 mm.

FIGURES 7–10. D. elongata n. sp., holotype female. 7. Habitus. Scale bar = ca. 1.0 mm. 8–10. Female terminalia. Scale bars = ca. 0.25 mm. 8. Dorsal. 9. Ventral. 10. Lateral. Abbreviations: c1, cercus one; c2, cercus two; s7, sternite seven; s8, sternite eight; s10, sternite ten; t7, tergite seven; t8, tergite eight, t10, tergite ten.

FIGURES 47–48. Distribution maps. 47. D. elongata n. sp. (yellow star) and D. sohnsi n. sp. (red circle). 48. D. potomaca (green circle) and D. euzona (red square); although no D. euzona specimens were examined from the District of Columbia, because D.C. is the type locality of D. euzona and is the most southern record known for the species, it has been plotted on the map.