Dixa inextricata Dyar & Shannon
Creators: name: Moulton, John K.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Dixidae
Dixa
Dixa inextricata

description: Dixa inextricata Dyar & Shannon
(Figs 11, 18–20, 22, 29–30)
Dixa inextricata Dyar & Shannon, 1924: 198. Edwards, 1932: 12 (checklist); Cooper & Rapp, 1944: 250 (checklist); Nowell, 1963: 96 (catalog); Hubert, 1965: 101 (catalog; known distribution); Peters & Cook, 1966: 244 (re-description; lectotype designated); Peters, 1968: 2 (primary type information).
Type material. LECTOTYPE (USNM Type No. 27452; Slide No. 2008) ♂, labeled: “[USA: VIRGINIA]: [FAIRFIELD COUNTY]/ Dixa / inextricata D. & S./ Type / Dead Run, Va/ R.C. Shannon/ [Slide No.] 2008”; “ Type No. 27452 U.S. N.M. [red label]” (USNM). PARALECTOTYPES: Same data as holotype, ♂ (Slide No. 2021); MARYLAND: [MONTGOMERY COUNTY], Plummers Island, 3♂ (USNM Slide Nos. 2018, 2022, 2024). Cabin John, ♂, L. O. Jackson, (USNM Slide No. 2017).
Additional material examined. CANADA: ONTARIO: Owen Sound, Inglis Falls Sprs, N44°31′33.15″ N W80°56′02.56″, 19.ii.1986, B.J. Sinclair—1♂; Same data, except 6.v.1986 —2♂. HALTON COUNTY, Rattlesnake Cons Area, nr. Buffalo Comp’d, N43°28′10.79″, W79°54′47.37″ W, 12.v.1990, B.J. Sinclair (3♂, CNC). USA: GEORGIA: TOWNS COUNTY, Chattahoochee NF, Rt. 180 W of Spur to Brasstown Bald, 862 m, N34°50′39.40″ W83°47′55.20″, 15.iii.2012, JKM—7♂, 5L; 27.iii.2012 —3♂, 8L; 14.iv.2012 —17♂, 2♀, 1P. WALKER COUNTY, Crockford-Pigeon Mtn WMA, Stream @ Keown Falls Trailhead ex Pocket Rd., N34°36′49.00″ W85°05′17.70″, 05.v.2012, JKM—1♂, 2L. KENTUCKY: HARLAN COUNTY, Blanton Forest State Nature Preserve, Watt Crk, 430 m, N36°51′36.95″ W83°22′54.17″, 28.v.2008, M.A. Floyd—3♂. LETCHER COUNTY, Bad Branch, 566 m, N37°04′12.01″ W82°46′17.99″, 8.vi.2007, JKM & M.A. Floyd—5♂, 3♀. Lilly Cornett Woods, Big Everidge Crk, ex KY Rt 113, 345 m, N37.0769° W82.996°, UV light trap, 23.vii.2009, M.A. Floyd—38♂, 11♀. WOLFE COUNTY, Red River Gorge Geological Area, small trib Red R nr Sheltowee Trace Trailhead, N37°49′37.53″ W83°37′26.73″, 9.vi.2015, JKM—15♂, 2♀. PENNSYLVANIA: ERIE COUNTY, Fourmile Crk, N42°08′15.71″ W80°00′35.85″, 1.vi.1992, E.C. Mastellar (1♂, PSU). PHILADELPHIA COUNTY, Wissahickon Park, S of Livezeys Ln, Trib. 3 of Wissahickon Crk, 43 m, N40°02′09.02″ W75°12′01.25″, 20.x.1998, J. Gelhaus (1♂, PAS). TENNESSEE: BLOUNT COUNTY, Small trickle @ Top of the World Dr, 24.iv.2009, JKM—1♂, 1L. CUMBERLAND COUNTY, Potter’s Ford, wet rock face, UV light trap, 17–18.vi.2007, C. Parker & J. Robinson (6♂, 6♀, USGS). FENTRESS COUNTY, Obed Wild and Scenic River NP, Staples Spr, N36°03′30.53″ W84°47′35.55″ W, 17.vi.2007, J. Robinson—6♂, 6♀. JEFFERSON COUNTY, Piedmont Branch @ Shield’s Ridge Rd, UV light trap, 9.viii.2006, JKM—1♀. VIRGINIA: CARROLL COUNTY, small crk nr. canoe rental ex. US Rt. 58, 10.ix.2005, JKM—1♂. FA I R FA X C O U N T Y, Dead Run, 14.iv.1914, R.C. Shannon (1♂, USNM); 13.iii.1915, R.C. Shannon (1♂, USNM); 18.iii.1915, R.C. Shannon (1♂, USNM); 13.iv.1925, R.C. Shannon (1♂, USNM). GRAYSON COUNTY, rivulet x-ing Meadow Beach Ln., ex CR 634, 783 m, N36°37′11.22″ W81°02′57.80″, 17.iii.2005, JKM—16♂, 1♀; 3.vii.2006 —1♂, 1♀; 17.viii.2007 —4♂, 2♀; 14.iv.2012 — 2P. PAGE COUNTY, Shenandoah NP, Big Meadows, 15.vi.1941, A.L. Melander (1♂, USNM).
Diagnosis. This species can be distinguished from D. appalachiensis sp. nov. and D. calciphila sp. nov. by the following characters: Morphological. Gonostylus 2X longer than its greatest depth when viewed laterally, with ventral margin nearly straight and apex not twisted medially; basal gonocoxal lobe subovoid, with posterior margin indented slightly and apex directed posteroventrally; cercus length half that of proctiger lateral width. Molecular. Among the most noticeable differences within the 66 nucleotides shown in Figure 38 that serve to distinguish this species from the other two are amino acid substitutions at the following codon positions (shown as triplets): 16 (proline vs. serine) and 19 (lycine vs. arginine).
Re-description. Male. Same as D. appalachiensis sp. nov., except as follows: Wing length (n =11) 2.5–3.2 (avg=2.8) mm. Male terminalia (Figs 11, 18–20): Cercus length half that of proctiger lateral width. Basal gonocoxal lobe subovoid, distal margin indented, apex directed posterodorsally. Apical gonocoxal lobe ca. 1/ 3X length of gonostylus. Gonostylus triangular in lateral view, 2X longer than greatest depth/width, with apex straight, not twisted ca. 90° medially as seen in ventral view (Fig. 19), ventral margin straight or nearly so, posterior margin more uniformly serrate.
Female. Wing length (n =5) 2.6–3.0 (avg=2.8) mm. Not reliably separated from D. appalachiensis sp. nov. or D. calciphila sp. nov.
Etymology. From the Latin prefix “ in -“ + Latin root “ extricat-“ meaning to release from an entanglement or difficulty.
Distribution. Dixa inextricata is the most widely distributed of the three members of this newly recognized species group. It is confirmed from Ontario south through PA, VA and MD into northern GA within and immediately adjacent to the central Appalachian Highlands (Fig. 37). Specimens examined by Peters from upper NY are hypothesized to belong to this species although I was unable to observe them personally.
Remarks. Dixa inextricata is found in and around small woodland streams ranging from spring seeps percolating through mud and leaf packs (Fig. 35) to larger and moderately flowing streams (Fig. 36) often having small riffles. It is sometimes associated with Dixa notata Loew in highland trickles and with D. fusca and D. terna Loew in lowland trickles. In streams near the upper threshold of its size preference, it is often found with the ubiquitous D. modesta sensu Peters. Adults are on the wing by mid-March in GA and VA. Records of specimens examined by Peters from upper NY are hypothesized to belong to this species based on suitable habitat. These specimens were not located in the USNM or the University of Minnesota collections.
Genetic evidence (J.K. Moulton, unpublished) shows some differentiation between populations in the Cumberland Plateau versus ones found in areas to the east. Known preimaginal habitats between these populations also differ in that the former are moderately flowing wider watercourses with riffles as opposed to tiny mostly mudbottomed ravine seepages. Armature of the bursa copulatrix in a specimen from Red River Gorge, KY (Fig. 29) possessed two groups of setae similar to what has previously been depicted for the species (e.g., fig. 64 in Peters & Cook 1966) but also a medial group of ca. 10 strong pegs. However, a Brasstown Bald, GA specimen (Fig. 30) possessed a medial group of ca. 40+ variably sized pegs.
description: Published as part of Moulton, John K., 2016, The Dixa inextricata Dyar & Shannon (Diptera: Dixidae) species group, with two new cryptic species from the eastern Nearctic Region, pp. 458-472 in Zootaxa 4121 (4) on pages 467-468, DOI: 10.11646/zootaxa.4121.4.6, http://zenodo.org/record/265286