Dixa falcata, Moulton, 2018

Moulton, John K., 2018, Rediscovery of Dixa repanda Peters and description of its putative sister species, Dixa falcata sp. nov., from the south-central United States (Diptera: Dixidae), Zootaxa 4459 (1), pp. 171-178 : 172-174

Dixa falcata sp. nov.

( Figs 1, 2 , 3 , 5, 7, 9, 11 )

Type material. HOLOTYPE ♂ (pointed), labeled: “ USA: GA: CATOOSA COUNTY/ Rock Cave Spring / Chickamauga National Military Park / N34°54′10.7″ W85°16′20.1″, 225 m / 25.vi.2013, J.K. Moulton ”; “ HOLOTYPE / Dixa / falcata / J.K. Moulton 2017 [red label]” (CNC) . PARATYPES [blue labels]: same data as holotype (2♂, CNC) ; same data as holotype, except 8–9.v.2007, C. Parker & J. Robinson (2♂, CNC) and (3♂, USNM) .

Additional material examined. USA: Alabama: DEKALB COUNTY, Rt 09-05 x-ing, UV light trap, 10– 11.vi.2007, C. Parker & J. Robinson (1♂; USGS) . Arkansas: MADISON COUNTY, Rt 74, 4.8 km W of Kingston, 24.iv.1989, C.R. L[oerch] & P.H. A[dler] (2L*) . POLK COUNTY, Quachita NF, Gap Crk @ Picnic Area , N34°28′33.07″ W94°07′03.78″, 355 m, 12.v.2007, J.K. Moulton (4♂) . SALINE COUNTY, Bread Crk , N34°47′36.0″ W92°58′29.1″, 299 m, 17.v.2001, A.L. Sheldon (3♂) ; 17.v.2001 (5♂) ; 2.vi.2001 (5♂) ; 22.vii.2001 (7♂) . Little Glazypeau Crk , N34°38′18.3″ W93°05′35.7″, 235 m, 16.iv.2001, A.L. Sheldon (1♀) ; 19.v.2001 (3♂, 4♀) ; 2.vi.2001 (3♂, 5♀) ; 9.vi.2001 (2♂ 1♀) ; 23.vii.2001 (4♂, 2♀) ; 2.viii.2001 (6♂, 4♀) . S Alum Crk , N34°48′00.6″ W93°00′24.6″, 310 m, 19.v.2001, A.L. Sheldon (6♂, 2♀) ; 10.vii.2001 (4♂, 1♀) ; 22.vii.2001 (9♂, 2♀) . STONE COUNTY, Ozark NF, underground str @ Hwy 5, 21.v.1991, B.J. Sinclair (1♂, 1♀, CNC) . Georgia: BARTOW COUNTY, Mosteller Spr @ Mosteller Spr Rd , N34°22′56.3″ W84°51′01.9″, 260 m, 17.vii.2013, J.K. Moulton (6♂, 2♀) . CATOOSA COUNTY, Chickamauga National Military Park, Rock Cave Spr , N34°54′10.7″ W85°16′20.1″, 225 m, UV light trap, 8–9.v.2007, C. Parker & J. Robinson (9♂, USGS) . Kentucky: BELL COUNTY, Cumberland Gap NHP, Tunnel Crk , N36°36′15.0″ W83°41′16.9″, 369 m, 28.ix.2005, J.K. Moulton (1♂) . EDMONSON COUNTY, Mammoth Cave NP, Echo Spr [N37°10′46.8″ W86°06′28.3″], 168 m, 9.vi.1991, B.J. Sinclair (3♂, CNC) . TAYLOR COUNTY, Little Angel Spr, Trib Craig’s Crk, N of Campbellsville , N37°26′40″ W83°21′18″, 312 m, 9.vi.2005, J.K. Moulton (1♂) . Missouri: RIPLEY COUNTY, small stream x-ing Hwy C nr Cupola Pond SNA, N36°48′42.2″ W91°05′04.6″, 239 m, 29.iv.2009, J.K. Moulton (1L*) . Oklahoma: MURRAY COUNTY, Chickasaw Nat’l Rec Area, Sulphur, Travertine Crk [N34°30′13.7″ W96°56′34.3″, 326 m], 13.v.1993, J.M. Cumming (1♂, CNC) . Tennessee: BRADLEY COUNTY, Red Clay SP, outflow of Council Spring ( Blue Hole ), N34°59′36.1″ W84°56′48.0″, 259 m, 25.v.2013, J.K. Moulton (5♂) . CHEATHAM COUNTY, Trib Marrowbone Crk @ Abernathy Rd , N36°16′08.9″ W86°57′16.8″, 219 m, 12.iv.2009, J.K. Moulton (6♂) . GRAINGER COUNTY, Avondale Spr , N36°17′00.5″ W83°32′04.5″, 308 m, 3.vi.2006, J.K. Moulton (1♂) . JEFFERSON COUNTY, Small trib Dumplin Crk @ Hebron Rd , N36°03′42.6″ W83°27′18.6″, 345 m, 5.v.2008, J.K. Moulton (7♂, 5♀) . KNOX COUNTY, small crk @ Pleasant Gap Baptist Church, N36°07′32.07″ W83°58′05.86″, 302 m, 3.vi.2006, J.K. Moulton (2♂) ; Fowler Spr Branch @ Bell Cmpgd Rd , N36°02′56.2″ W084°04′07.8″, 288 m, 11.x.2005, J.K. Moulton (2♂, 1♀) . LINCOLN COUNTY, Harmony Spr @ TN50 S of Lynchburg , 11.iv.2011, J.K. Moulton (2♂) . MARION COUNTY, Daniel Cave Spr , N36°15′39.2″ W85°28′47.2″, 332 m, 8.ix.2010, J.K. Moulton (1♂) . MAURY COUNTY, Big Bigby Crk @ Rt 166, N35°39′05.3″ W87°14′49.0″, 178 m, 12.v.2010, B.H. Bauer (1♂) ; Sugar Crk @ Old railroad x-ing, 23.vi.2010, B.H. Bauer (1♂) . Virginia: NELSON COUNTY, small (1–2 m) str @ BRP, 1.8 km from NP entrance, 611 m, N38°01′21.6″ W79°07′50.2″, UV light trap, 16–17.vii.2007, C. Parker & J. Robinson (1♂, USGS) .

Diagnosis. The apically tapered falcate gonostylus with numerous, strongly developed medial setae, large subrectangular basal gonocoxal lobe, and obliterated cercus distinguish this species from all others in the Nearctic Region.

Description. Male ( Fig. 1 ). Wing length (n =10) 2.8–3.4 (avg=3.0) mm. Head, antenna, and mouthparts brown. Antenna ca. 2/ 3X length of wing, clothed with whorls of short setae; pedicel small, collar-like; scape globose, ca. 4X width of flagellomere I. Flagellum with 14 articles. Flagellomere I cylindrical, 1.6X length of flagellomere II. Flagellomeres I and II most notably subcylindrical, with remaining flagellomeres increasingly shorter and cylindrical. Flagellomere XIV with pair of divergent apical setae. Maxillary palpus 5-segmented; ratio of segment lengths (proximal to apical) 1:2:6:10:12. Scutum dark brown, lacking prominent stripes unless teneral, in which case thick median stripe present. Pronotal lobe brown, with 2 short and 1–2 long apical setae. Postnotum with 1 prominent seta. Anepisternum and anepimeron dark brown, bare. Katepisternum dark brown, with 3–5 setae medially. Katepimeron brown, bare. Metepisternum and metepimeron light brown, bare. Laterotergite brown, bare. Legs with coxae straw-colored and distal segments brown. Pro- and mesothoracic legs symmetrical, with following segment length ratios [coxa, trochanter, femur, tibia, t1, t2, t3, t4, t5 (including claw)]: 2.5, 1, 15, 15, 11, 4.3, 2.5, 1, 2.5. Metathoracic legs differing in that t1 and t4 ca. 33% longer. Coxae light brown, setose anterolaterally. Foretibia not expanded apically. Fore- and mesotarsal claws pectinate, with 4–5 prominent subapical tines, often with additional smaller ones. Metathoracic claw with 1 mesal and 1 basal small secondary tines, sometimes with third one between them. Pro- and mesotibia not noticeably expanded apically. Metafemur expanded apically, with transverse row of ca. 12–14 uniformly sized setae on bulge. Tarsomeres 3 and 4, most noticeably of meso- and metathoracic legs, with variably thickened, sometimes hooked, proximal seta on ventral surface. Wing light gray, lacking infuscation at junction of Rs, R2+3, R4+5 and crossvein r-m. Wing veins brown, setose. Rs arising near terminus of Sc. R2+3 proximal to crossvein r-m. Crossvein m-m weakened. False vein (FV) distinct from and parallel to CuA for most of its length. Halter brownish gray apically, with stem straw-colored. Scutellum brown, with ca. 12 posteriorly directed transverse setae along posterior margin. Abdomen dark brown, with pink/purple and blue/green iridescence. Basal fringe brown. Segments 2–6 with dark brown tergites and grayish brown pleural regions. Segments 7–9 dark brown. Terminalia ( Figs 3 , 5, 7, 9, 11 ): Tergite 9 subtrapezoidal, with anterior margin convex. Sternite 9 subrectangular. Proctiger sub-square in lateral view, with digitiform ventral process articulated with subepandrial sclerite. Cercus reduced to barely perceptible, knuckle-like lobe not protruding beyond posterolateral margin of proctiger. Epiproct ovoid, lightly sclerotized. Subepandrial sclerite bilobed, with proximal lobe acute and distal lobe broadly rounded apically, latter narrow lip beneath proctiger when viewed dorsally. Gonocoxite subcylindrical, nearly as long as broad, with prominent basal and apical lobes. Basal gonocoxal lobe large, 0.75–0.80X gonocoxal width, subrectangular, with setae on inner surface and sparse apical spinules, in lateral view proximal margin nearly reaching anterior margin of gonocoxa and posterior margin extended to base of apical gonocoxal lobe. Apical gonocoxal lobe short, ca. 1/ 6X length of gonostylus in lateral view, with numerous, prominent setae along posteroventral margin. Anterior margin of basal gonocoxal lobe intimately associated with gonocoxal apodeme, paramere base, ventral plate, and penis sheath. Penis sheath short, broad, trough-like, curving anterodorsally from origin near gonocoxal apodeme before continuing on posteriorly towards junction of parameres and ventral apodeme of subepandrial sclerite. Penis filament concomitantly short, sclerotized only at apex, nearest gonopore. Gonostylus falcate, ca. 2.3X longer than greatest width/height, tapered apically (Figs 21, 49); lateral surface clothed with short, posteriorly directed setae; medial surface clothed with longer, stouter setae; dorsal margin convex, tallest anterior to midlength, with strong medially derived setae protruding well beyond margin for entire length; dorsal margin convex, with short setae running entire length; apices twisted 90° medially. Aedeagus in terminal view hastate to heart-shaped, membranous, covered with spicules, positioned between straplike parameres. Ventral plate deeply divided medially into roughly diamond-shaped to hexagonal halves, connected by thin anterior strap.

Female ( Fig. 2 ). Differing from male as follows: Body coloration overall lighter. Wing length (n =8) 3.0–3.4 (avg=3.2) mm. Antennal segments more robust. Tarsal claws non-pectinate. Abdomen with nonsclerotized pleural region widened, with iridescent pink-purple sheen laterally. Terminalia: 9T subrectangular. 9S strap-like, posterior margin distended medially. 10S divided into pair of thin triangular lobes, apices 2X width of proximal portion of structure before meeting medially. Cercus in lateral view hemi-ovoid, thickened and directed posterodorsally. In dorsal and ventral views lateral and medial margins of cercus convex and concave, respectively and apices slightly convergent. Bursa copulatrix armed with two groups of tooth-like spines of varying size. Spermatheca golden brown, spherical, with weak surface sculpturing and short sclerotized neck at junction with bottlebrush-like duct.

Etymology. The species epithet is in reference to the shape of the male gonostylus.

Distribution and bionomics. This species occurs primarily in and around small, slow flowing, first-order calcareous springs often containing varying amounts of watercress and with or without a canopy ( Fig. 12 ). The known range of Dixa falcata sp. nov. extends from southwestern Virginia to Missouri and Oklahoma, south to northern Georgia, Alabama, and central Arkansas ( Fig. 14). Larvae mature by April to May, with adults common from May until October or perhaps later in some years. Throughout its known range, it is commonly associated with D. ubiquita Moulton and, in central TN and KY, also with D. calciphila Moulton.

Remarks. On the basis of similarity in the male gonostylus as well as ample molecular data (J.K. Moulton, unpublished), this species appears to be the sister to D. falcata sp. nov. The female is similar to those of several other similarly colored, related species. When associated only with D. ubiquita , females of D. falcata sp. nov. can be separated by the absence of a faint wing spot at the junction of Rs and R2+3. When associated with D. calciphila , which also lacks a wing spot, female identification is tenuous at best.

Figures

FIGURES 1–2. Dorsal habitus. 1, Dixa falcata sp. nov., ♂. 2, D. falcata sp. nov., ♀. Scale bar = 1 mm.

FIGURES 3–4. Male terminalia, illustrated in lateral view. 3, D. falcata sp. nov. 4, D. repanda. Scale bar = 50 µm.

FIGURES 5–11. Male terminalia. 5–6, lateral view. 5, Dixa falcata sp. nov. 6, D. repanda. 7–8, ventral view. 7, Dixa falcata sp. nov. 8, D. repanda. 9–10, terminal view. 9, Dixa falcata sp. nov. 10, D. repanda. 11, D. falcata sp. nov., dorsal view. The red arrow in Fig. 11 denotes the reduced cercus. Scale bar = 50 µm.

FIGURES 12–13. Example habitats for D. falcata sp. nov. and D. repanda Peters. 12, Fowler Spring Branch, Powell, TN. 13, Black Bridge Spring, NNE of Balltown, IA.