Ischnomyia albicosta ( Walker, 1849 )

Roháćek, Jindřich & Barber, Kevin N., 2016, Nearctic Anthomyzidae: a monograph of Anthomyza and allied genera (Diptera), Acta Entomologica Musei Nationalis Pragae (suppl.) 56, pp. 1-412 : 45-55

Ischnomyia albicosta ( Walker, 1849)

( Figs 47–65 )

? Diastata albicosta Walker, 1849: 1113 . Ischnomyia albicosta: CZERNY (1902) :255 (generic combination); HENDEL (1911): 46 (diagnosis); MELANDER (1913): 293 (key); SABROSKY (1965): 819 (catalogue); ROHÁĆEK (1998a): 174 (checklist). Ischnomyia vittula Loew, 1863: 325 ; CZERNY (1902): 255 (synonymy); ALDRICH (1905): 644 (catalogue). Ischnomyia vittata: OSTEN SACKEN (1878) : 198 (misspelling, catalogue). Tachydromia vittipennis: SMITH (1971) : 367 (incorrect synonymy with I. albicosta ).

Type material. Diastata albicosta Walker : NEOTYPE: ♂ (designated herewith) labelled: “ONT: Burlington, Royal Botanical Gdn, 15.vii.2002, KNBarber, sweeps, trailside vegetation in mixed hardwood 48°17.8'N 79°52.6'W ”, “ NEOTYPUS ♂, Diastata albicosta Walker, J. Roháček & K. N. Barber des. 2013” (red) and “ Ischnomyia albicosta (Walker) ♂, J. Roháček & K. N. Barber det. 2013” ( BMNH, in perfect condition, intact, see Fig. 48 ).

Ischnomyia vittula Loew : LECTOTYPE: ♂ (designated herewith) labelled: “Penn.”, “Loew Coll”, “Type 13426” (red), “ LECTOTYPUS ♂, Ischnomyia vittula Loew, J. Roháček & K. N. Barber des. 2013” (red) and “ Ischnomyia albicosta (Walker) ♂, J. Roháček & K. N. Barber det. 2013”. PARALECTOTYPE: ♀ labelled: “Loew Coll”, “vittata m.” (Loew’s handwriting), “Type 13426” (red), “ PARALECTOTYPUS ♀, Ischnomyia vittula Loew, J. Roháček & K. N. Barber des. 2013” (red) and “ Ischnomyia albicosta (Walker) ♀, J. Roháček & K. N. Barber det. 2013”. Both specimens are in rather good condition, in the lectotype the left wing is lost, in the paralectotype both antennae are missing ( MCZC, intact).

Other material examined. CANADA: ONTARIO: Burlington, Royal Botanical Gardens , 43°17.8'N 79°52.6'W, sweeps, trailside vegetation in mixed hardwood, 14.vii.2002, 3 ♂♂ 2 ♀♀ ( DEBU 2 ♂♂ 1 ♀, 1 ♀ genit.prep., SMOC 1 ♂ 1 ♀, both genit. prep.), 15.vii.2002, 2 ♂♂ 1 ♀ ( CNCI, ♀ genit. prep.), 16.vii.2002, 1 ♂ 4 ♀♀ ( CASC 1 ♂ 1 ♀, CNCI 3 ♀♀), 18.vii.2002, 2 ♂♂ 2 ♀♀ ( CNCI, 1 ♂ wing illustration) ; same locality but 43°17.79'N 79°52.61'W, trailside sweeps, mostly Carex , Fragaria , Solidago , 27.vii.2003, 6 ♂♂ 3 ♀♀ ( AMNH 2 ♂♂ 1 ♀, DEBU 2 ♂♂, SMOC 2 ♂♂ 2 ♀♀), all K. N. Barber leg. ; Russell Co., Cumberland , [-]. vii.1975, 1 ♀, L. Ling leg. ; Guelph , new orchard, 25.vii.1981, 1 ♂, Mark Eymann leg. ; Guelph , 23.vii.1982, 1 ♀, K. Barber leg. (all DEBU) ; Ottawa, MacKay Lake Outlet , 6.viii.2006, 1 ♂, J. R. Vockeroth leg. ( CNCI, Diptera #58950) ; Point Pelee , 17.vii.1978, 1 ♀? ( DEBU 00006171 , legs and abdomen missing), 1 ♂ 1 ♀ (♀ with DEBU 00006172 ), W. A. Attwater leg., 18.vii.1978, 1 ♂ ( DEBU 00006170 ), 20.vii.1978, 1 ♀, D. Morris leg. ( DEBU 00006173 ) . QUEBEC: Terrasse-Vaudreuil Molson Nature Reserve , 45°23.57'N 73°58.81'W, sweep path in forest, 1.vii.1999, 1 ♀, T. A. Wheeler leg. ( LEMQ). UNITED STATES OF AMERICA: DISTRICT OF COLUMBIA: Washington , [-].viii.[18]97, 1 ♀, F. C. Pratt leg. ( USNM); Washington, Deanwood , nr. brook, 9.vi.1991, 1 ♀, M. Barták leg. ( MBPC) . GEORGIA: Rabun Co., Pine Mountain , 1400', 14.v.1957, 1 ♀, W.R. M. Mason leg. ; Rabun Co., Warwoman Creek , 1500', 26.vii.1957, 1 ♂ (genit.prep., only right wing remaining on pin), J. G. Chillcott leg. (both CNCI) . ILLINOIS: Union Co., Shawnee National Forest, Pine Hills Campground, #83039-042, 9.vi.1983, 1 ♂ 1 ♀, I. S. Askevold leg. ( DEBU) . INDIANA: Jefferson Co., Henslers Woods nr. Hanover , 16.vi.1921, 1 ♂ 1 ♀, C. P.Alexander leg. ; Lafayette , 11.vi.1916, 1 ♂ (missing head and 1 wing), 7.vii.1916, 1 ♀, 13.vii.1916, 1 ♂ (headless), J. M. Aldrich leg., 4.viii.1914, 1 ♂, A. L. Melander leg. ; Turkey Run , 27.vi.1933, 1 ♂ (headless), A. L. Melander leg.(all USNM) . MARYLAND: Cabin John , 20.vi.1931, 1 ♂, A.L.Melander leg. ; Cabin John Br. , 21.vi. [-], 1 ♂, J. M. Aldrich leg. ; Montgomery Co., Carderock Park , 13.vi.1970, 1 ♂, L. V. Knutson leg. ; Glen Echo , 18.vi.1922, 1 ♂, J. R. Malloch leg. ( BYUC) ; Glen Echo , 8.viii.1921, 1 ♀, 21.viii.1921, 2 ♀♀, 11.vi.1922, 1 ♂ 1 ♀, 18.vi.1922, 1 ♀, 1.vii.1923, 1 ♀, J. R. Malloch leg., 22.viii.1922, 1 ♂, W. L. McAtee leg. ; Plummers Island , 27.viii.1913, 1 ♀, H. S. Barber leg., 17.viii.1906, 1 ♀, Barber & Schwarz leg., 17.vi.1913, 2 ♂♂ (1 ♂ with only abdomen and 2 wings remaining), J. D. Hood leg., 21.vii.1907, 1 ♂, 7.vi.1914, 2 ♀♀, 4.vii.1914, 1 ♂, 26.vii.1914, 1 ♂, W. L. McAtee leg., 19.vi.1913, 1 ♀, R. C. Shannon leg. ; Plummers Island , at light, 13.vi.1914, 1 ♀, 3.viii.1915, 1 ♂ 2 ♀♀, R. C. Shannon leg., 8.vi.1914, 1 ♂, Schwarz & Shannon leg. ; Sligo , 27.vi.1928, 1 ♂, J. M. Aldrich leg. (all USNM) . MASSACHUSETTS: Catoctin, Mt. Park, Owen’s Creek , 15.vi.1991, 1 ♀ (genit. prep.) ; Catoctin, Mt. Park ( Lantz ), 15.vi.1991, edge of wood, 1 ♂, meadow nr. pond, 1 ♂ (genit. prep.), all M. Barták leg. (all MBPC) ; Franklin Co., ~ 0.5 km E Farley , 42°36.16'N 72°25.94'W, sweeps, asters, ferns, Impatiens , Rubus , under canopy, 26.vii.2006, 4 ♂♂ 3 ♀♀, K. N. Barber leg. ( CNCI 2 ♂♂ 1 ♀, LACM 2 ♂♂ 2 ♀♀) ; Middlesex Co., Lincoln , Malaise trap, 7.vii.1982, 1 ♀, E. T. Armstrong leg. ( USNM) . MICHIGAN: Ingham Co., East Lansing , 9.vii.1971, 1 ♂, D. D. Wilder leg. ; Newaygo Co., 27.vi.1953, 1 ♀, R. R. Dreisbach leg. (both USNM) . MINNESOTA: Olmsted Co., [no date], 1 ♀, C. N Ainslie leg. ( CNCI, headless) . NEW YORK: [no further data], 1 ♂, A. H. Sturtevant leg. ( USNM) ; Ithaca, Six Mile , 24.vii.1958, 2 ♂♂, D. F. Beneway leg. ( SEMC, 1 headless) ; Poughkeepsie , 7.vii.1936, 1 ♂ 1 ♀, H. K. Townes leg. ( USNM, triple mount (single pin) with 1 ♀ Arganthomyza vittipennis ) . NORTH CAROLINA: Transylvania Co., Cove Creek Campground, Davidson River , 35.2814°N 82.8142°W, 780 m, sweep path by river, 17.vi.2008, 1 ♀, J. Mlynarek leg. ( LEMQ) ; Mitchell Co., Penland , 3000', 19.vi.1957, 1 ♂ 2 ♀♀, G. Steyskal leg. ( USNM) ; Wayah Bald , 10.viii.1957, 1 ♀, L. A. Kelton leg. ( CNCI, headless) . OHIO: 3.0 mi N Kent, Herrick Fen , 16.vi.1986, 1 ♂, B. A. Foote leg. ( CNCI) . PENNSYLVANIA: Bradford Co., Wilawana , 21.vii.1991, 1 ♀, R. H. Crandall leg. ( LACM ENT 329118 ) ; Natrona, [date illegible], 1 ♂, [no collector] ( USNM) . TENNESSEE: Blount Co., GSMNP [Great Smoky Mountains National Park], Cades Cove, Forge Creek Rd. , 35°35'03"N 83°50'17"W, ex. forest, 14.vi.2008, 1 ♂, B. J. Sinclair leg. ( CNCI) ; Cades Cove , GSMNP, sweeps, 5.vi.1979, 6 ♂♂ 3 ♀♀, M. J. Sharkey leg. ( DEBU, 2 ♂♂ 1 ♀ genit. prep., all in generally poor condition) ; Sevier Co., Great Smoky Mtns. Nat. Pk., Elkmont Campground , ex. yellow pan traps, 14–16.vi.1990, 1 ♀, B. J. Sinclair leg. ; Great Smoky Mt. National Park, Greenbrier Cove , 2000', 18.vi.1957, 1 ♀, J. R. Vockeroth leg. (both CNCI) . VIRGINIA: Bon Air , 16.viii.1936, 1 ♀, [no collector] ; Chain Bridge , 20.viii.1922, 1 ♀, J. R. Malloch leg. ; Alexandria Co., Maywood , 4.vi.1922, 1 ♀, J. R. Malloch leg. (all USNM) ; Washington Co., Mt. Rogers N. R. A. [National Recreation Area], Beartree , 36.65626°N 81.68957°W, sweep forest at reservoir, 16.viii.2007, 1 ♂, J. Mlynarek leg. ( LEMQ 0040775 ) ; Veitch , 9.vi.1912, 1 ♀, J. R. Malloch leg. ( USNM) . WEST VIRGINIA: Lost River State Park , 2.vii.1941, 1 ♀, A. Stone leg. ( USNM) . WISCONSIN: Polk Co., [-].vii.[-], 1 ♂, Baker leg. ( LACM ENT 329104 ) .

Redescription. Male. Total body length 2.18–2.80 mm; largely dark brown with yellow to white pattern ( Fig. 48 ), sparsely grey microtomentose and relatively shining. Head distinctly longer than high and angular in pronle ( Fig. 47 ), with frons somewhat projecting anteriorly, dark brown and yellowish white. Occiput dorsomedially concave, largely dark brown, but with a pair of medial yellow stripes originating above the foramen and running vertically to connect with the pale orbits; also ventrolateral corners of occiput (and postgena) yellow. Most of occiput sparsely light grey microtomentose and subshining but medial yellow stripes silvery white microtomentose (particularly dense above foramen) and connected with silvery stripes on head vertex and orbits. Frons with broad medial area (band) dark brown to blackish, microtomentose and dull, only frontal and ocellar triangle less dark grey microtomentose and slightly shining. Orbits broadly white to whitish yellow and silvery white microtomentose, most densely so anteriorly at frontal margin and posteriorly between posterior ors and vti; this silvery microtomentose stripe reaching posteroventrally far onto occiput (see above). Frontal triangle small, short and narrow, slightly broader than ocellar triangle and reaching to half (or less) of frons. Ocellar triangle darker, almost black, somewhat elevated and ocelli relatively large. Frontal lunule blackish brown (in contrast to I. barbarista ), relatively long but transverse. Face very narrow, weakly sclerotized medially and concave, largely brownish grey but dorsally and ventrally often paler to dirty yellowish white, all microtomentose and dull, laterally distinctly dark brown-margined. Parafacialia and gena whitish yellow and silvery white microtomentose; the dark brown and wider marginal stripe bordering parafacialia continued on ventral margin of gena but gradually faded and narrowed, posteriorly pale ochreous. Postgena and ventrolateral corner of occiput whitish yellow and sparsely whitish microtomentose. Mouthparts whitish yellow including palpus and clypeus. Cephalic chaetotaxy: pvt nne but comparatively long and strongly crossed; oc longest of cephalic setae but vti and posterior ors also very long; oc slightly divergent; vte slightly to hardly shorter than vti; 3 ors, posterior and middle both long with the middle slightly shorter than posterior, and the anterior ors reduced to a setula; 1 microsetula (about as long as medial microsetulae) in front of anterior ors; usually only 1 pair of minute medial microsetulae in front of anterior corner of frontal triangle; 1–2 setulae behind vte reduced; postocular setulae sparse (only 6–7), in single row; lateroventral corner of occiput and postgena with a few scattered setulae and 2 (1 longer) posteroventral nne setae; 1 long vi (about as long as but weaker than middle ors); subvibrissa well developed, up to three-fourths of vi; 5–6 very nne peristomal setulae. Palpus slender, whitish yellow, with 1 nne dark ventral preapical seta (shorter than subvibrissa) and more (up to 12) paler ventral and ventrolateral setulae. Eye large, elongately subovoid, with longest diameter longitudinally oblique and about 1.4 times as long as shortest. Smallest genal height about 0.11 times as long as shortest eye diameter. Antenna geniculate; scape and pedicel brown, the latter paler brown on inner side; 1st nagellomere ( Fig. 47 ) nattened, bicolourous, largely whitish but dark brown in narrower dorsal half; its anterior margin with very long white pilosity (longer than cilia on arista). Arista dark brown, with thickened basal segment, about 1.7–1.8 times as long as antenna, with relatively dense and long brown cilia, being most dense but shorter in front of basal segment.

Thorax slightly narrower than head, bicolourous, dark brown dorsally, yellowish white ventrally ( Fig. 48 ), with greyish microtomentum, duller dorsally, more shining laterally. Mesonotum brown to dark brown, with 3 narrow, yellow to orange ochreous vittae, 2 on dc lines (reaching slightly beyond anterior dc seta) and 1 similar but usually shorter and narrower medial stripe; humeral callus and notopleural area also paler, orange ochreous. Pleural part of thorax with longitudinal dark brown band across the whole thorax and as wide as half of mesopleuron ( Fig. 48 ). Ventral (larger) area of pleural part yellowish white. Mesonotum with reduced number of microsetae; all macrosetae long. Thoracic chaetotaxy: 1 hu (slightly shorter than anterior npl); 2 npl (posterior distinctly shorter and weaker); 1 long prs (as long as anterior npl); 1 long sa (as long as prs); 1 pa (shorter than sa); 2 very long postsutural dc (posterior longest of thoracic setae, anterior shorter but also very long, longer than prs) and 5–6 dc microsetae in front of them; ac microsetae sparse and small, in 2 medial rows only (at most with single lateral ac microseta in front of suture) and reaching to level of anterior dc; 2 sc, laterobasal small and weak (shorter than posterior sa), apical very long, almost as long as posterior dc (apical sc pair with apices usually meeting or crossed); 1 ppl, reduced to microseta; 2 relatively long but thin stpl, anterior somewhat shorter and weaker, and 3–4 upcurved dark setulae below, 1 between and 1 in front of stpl; ventral part of sternopleuron with 4 longer pale setae. Scutellum rounded triangular, slightly convex dorsally.

Legs whitish yellow, only distal half of apical tarsal segments darker yellow to ochreous ( Fig. 48 ). f 1 with ctenidial spine reduced ( Fig. 51 ), much shorter than maximum width of t 1, and with a row of very long posteroventral setae (usually longer than those in posterodorsal row). f 3 with a row of sparse (12–14) posteroventral setae along entire length, 6–7 of which in distal third are shortened and thickened; t 2 with relatively short ventroapical seta; mid basitarsus uniformly setulose; fore and hind basitarsus with slightly prolonged proximoventral hair-like setula (thus without thickened setae). f 2, t 1 and t 3 simply setulose. Wing ( Fig. 49 ) relatively narrow and long, widest in distal fourth, with pale ochreous to brown veins and distinctively patterned membrane. Wing pattern strikingly similar to those of Arganthomyza vittipennis and Epischnomyia species in having whitish hyaline band along C and R 2+3, dark brown, distally dilated middle band along R 4+5, and paler brown area at posterior margin of wing, but differs by having distinct additional longitudinal pale stripe between R 4+5 and M and very narrowly dark-bordered veins M and CuA 1. C with distinct spinulae between apices of R 1 and R 2+3. R 2+3 long, distinctly sinuate (more than in Epischnomyia species), not wholly parallel to C and with apex distinctly upcurved to C; R 4+5 slightly bent (recurved) and apically very slightly divergent from M. Discal (dm) cell narrow, with r-m situated (usually distinctly) in front of the middle of dm cell. Apical portion of CuA 1 longer than dm-cu, and reaching (with its colourless end) wing margin; A 1 short, ending far from it. Alula small, narrow; anal lobe relatively small. Wing measurements: length 2.34–2.82 mm, width 0.69–0.93 mm, Cs 3: Cs 4 = 1.52–1.96, rm\dm-cu: dm-cu = 2.36–3.67. Haltere with brown to dark brown knob and paler brown stem.

Abdomen dorsally (T1–T5, S8) dark brown, moderately setose, sparsely greyish microtomentose and relatively shining. Preabdominal terga with microtomentum reduced and more lustrous laterally. T1 and T2 distinctly dorsally separate, laterally fused. T3–T5 subequal in length but T5 slightly narrower, all broad and bent onto ventral side of abdomen. Preabdominal sterna ( Fig. 50 ) relatively broad, well sclerotized and brown-pigmented. S1 short, transverse, about twice as wide as long, bare, with darker-pigmented transverse stripe at posterior margin; S2 about as large as S3 but paler, setose in only posterior two-thirds; S3–S5 becoming larger and wider posteriorly; S3 narrowest, longer than broad, S4 as long as broad, widest posteriorly, both more setose than S2; S5 largest and widest, transverse, with distinctive pattern ( Fig. 50 ): brown-pigmented only at anterior and lateral margins, with large subtriangular posteromedial area unpigmented and with distinctive microtomentum. T6 very short, transversely band-like, slightly wider than T5, pale ochreous brown only laterally, otherwise largely faded to unpigmented, bare. S6–S8 dorsally fused together. S6 largely pale brown, with only anterior margin dark brown; S7 darker (almost as is S8), more shining, and also with blackish brown anterior margin; both S6 and S7 asymmetrical; S6 with 3–4, S7 with 2 setae; S8 long (markedly longer than epandrium) and distinctly tapered posteriorly, dark brown as epandrium and with a number of setae in posterior two-thirds.

Genitalia. Epandrium ( Figs 52, 53 ) blackish brown, moderately long but relatively broad and long setose, with 2 pairs of thicker and long setae (1 dorsomedial longest); anal nssure very broadly subtriangular (though less than in I. barbarista ). Cercus large and robust, pale brown-pigmented, densely and long setose, with apical seta very long. Medandrium ( Fig. 52 ) rather low but broad, dorsally tapered, with dorsolateral corners angular and more projecting than those of I. barbarista . Gonostylus ( Figs 52, 53 , 59 ) lighter brown than epandrium, narrow in lateral view (see Fig. 53 ), slightly bent medially, elongate oval, apically narrowed in outline (in widest extension view – Fig. 59 ) and terminating in 2 blunt teeth (very similar to that of I. barbarista but slightly broader); outer side largely micropubescent (in I. barbarista gonostylus is bare in distal third) while setae are mainly situated on inner side and at posterior margin. Hypandrium ( Figs 54, 56 ) relatively robust (including anterior part), with reduced anterior internal lobes. Transandrium ( Fig. 55 ) simple, band-like, medially projecting in distinctive caudal process similar to that of I. barbarista , i.e. well sclerotized and pigmented, and forming a forked sclerite with strikingly dilated apical (internally) arms. Pregonite ( Figs 54, 56 ) low, fused to hypandrium; anterior part shallowly bulging (in contrast to that of I. barbarista ) and with 4 setae (1–2 shorter), posterior part with relatively robust blunt process with 4–5 apical setae (1 longer). Postgonite ( Figs 54, 56 ) simple, slender, slightly elongate, S-shaped in lateral view (longer than in I. barbarista ), with tapered apex and several minute sensillae externally but without distinct setula (also absent in I. barbarista ). Basal membrane ( Figs 54–56 ) with dark, dense spine-like tubercles below caudal process (also ventromedially in contrast to I. barbarista ). Aedeagal part of folding apparatus ( Fig. 58 ) with dark-pigmented striae (visible in Figs 54, 56 ) and relatively robust, dark and dense lenticular to tooth-like excrescences (including those more internal). Connecting sclerite very slender, weakly sclerotized and pale, distally armed with nne spinulae ( Fig. 58 ). Phallapodeme long and robust, with basal part somewhat forked, fulcrum robust and apex very enlarged (more than in I. barbarista ), laterally widened and bicuspidate ( Fig. 58 ). Aedeagus with short, compact, frame-like phallophore. Distiphallus ( Fig. 58 ) relatively small (compared to phallapodeme), with short basal sclerites. Saccus proximally narrow and well sclerotized, distally dilated (less than that of I. barbarista ) and membranous and provided with several larger cup-like tubercles, otherwise unarmed (as in I. barbarista ). Filum short as in I. barbarista but more slender; formed by a pair of broad, closely-attached to partly-fused ribbon-like sclerites, ventral shorter and distally dilated, dorsal one attenuate, distally curved and ending in largely membranous, very nnely spinulose and denticulate apex ( Fig. 57 ). Ejacapodeme relatively large and elongate, with dark, clubbed medial projection ( Fig. 58 ).

Female. Similar to male unless mentioned otherwise. Total body length 2.65–3.45 mm. Face sometimes paler-pigmented; palpus often with slightly darkened tip. Orange yellow vittae on mesonotum usually longer including the medial one. f 3 posteroventrally simply setulose. Wing measurements: length 2.85–3.38 mm, width 0.81–1.13 mm, Cs 3: Cs 4 = 1.52–1.80, rm\ dm-cu: dm-cu = 2.68–3.25. Abdomen with preabdominal terga distinctly shorter and more transverse. T1 and T2 slightly narrower than T3–T5; T1 narrowest, shortest and very shortly setulose. T3 usually shorter than T4 and T5 which are subequal in length, all sparsely setose. Preabdominal sterna somewhat narrower than in male, becoming slightly wider posteriorly, all nnely setose. S3 longer than broad; S2, S4 and S5 about as long as broad; S5 largest and as wide as S6 which is markedly shorter and more transverse than S5.

Postabdomen ( Figs 60, 64 ) relatively short and wide (but more elongate than in I. barbarista ). T6 large, dark brown, broad anteriorly and narrower posteriorly, distinctly longer than in I. barbarista and setose in posterior two-thirds. S6 less transverse than that of I. barbarista , brown but with pale-pigmented margins ( Fig. 64 ) and sparsely setose. Contrary to the situation in I. barbarista , T7 and S7 are not fused but separate ( Fig. 64 ) though only narrowly separated along lateral margins. T7 semicylindrical, reaching far ventrally, markedly narrower and longer than tergosternum T7+S7 of I. barbarista , yet darker than T6 and rather densely setose in posterior two-thirds ( Fig. 60 ). S7 nat and dark brown ( Fig. 64 ), relatively large (as long as wide), with sparse but long setae, particularly at posterior and lateral margins. T8 small, nat, almost as long as wide, slightly emarginate posteriorly, brown-pigmented, with nne setae at posterior and lateral margins. S8 slightly shorter but wider than T8, medially divided to form 2 nnely setose sclerites having posterior bare, recurved and invaginated parts (eversible during oviposition). Genital chamber (uterus) with complex and brownpigmented internal sclerotization ( Figs 62, 65 ) being anteriorly formed by several fused sclerites (this part somewhat resembling that in I. barbarista ) and posteriorly by 1 very nne, palepigmented, elongate (in ventral view of pyriform outline), strongly bent annular sclerite. [Note: The structure, considered to be a modined annular sclerite in I. barbarista (see OHÁĆEK 2009a: Fig. 85 ) is in fact only the ventral part of the anterior complex of sclerites, while the true annular sclerite is apparently unpigmented and has therefore been overlooked in the latter species]. Ventral receptacle ( Fig. 65 ) hyaline, simple, slender proximally and somewhat dilated distally, not very long, bent ventrally, with distal conical end very nnely ringed and with blunt tip ( Fig. 63 ); accessory gland hyaline, poorly visible, on slender but distally dilated (sometimes doubly) and partly ringed duct. Spermathecae (1+1) very similar to those of I. barbarista , broadly ovoid, one somewhat larger than other, with nnely ringed surface except for basal nfth being provided with a very few (2–4) minute spinulae; each with small terminal invagination, eccentric duct insertion (see Figs 61 ) and very pale-pigmented and short cervix; duct of spermatheca very long (as in Anthomyza species). T10 small, transverse, very sparsely micropubescent and pale brown, with 1 pair of very long medial setae (see Fig. 60 ). S10 markedly larger than T10, rounded triangular, largely micropubescent (differing in this from partly micropubescent S10 of I. barbarista ) and long nne setae at posterior margin ( Fig. 64 ). Cercus relatively short, more slender than in I. barbarista , with nne setae, apical and dorsopreapical being longest ( Figs 60, 64 ).

Discussion. The species was described by WALKER (1849) with uncertain generic placement (in? Diastata ). CZERNY (1902) recognized it as an older synonym of Ischnomyia vittula Loew, 1863 , the type species of the genus Ischnomyia . Because the type specimens of I. albicosta are absent in the F. Walker Collection (BMNH) and have not been traced to other collections and museums, they are considered lost. Therefore, a neotype (a male from Canada) is designated here to nx the concept of the species following the redescription by CZERNY (1902). To connrm its synonymy with I. vittula Loew , all available syntypes of the latter were examined and the lectotype (male) designated. The incorrect spelling “ vittata ” (nrst used by OSTEN SACKEN 1878) originates from the name used on Loew’s original label which remains on one of the type specimens despite the name being changed in the publication ( LOEW 1863) to “ vittula ”. Tachydromia vittipennis Walker, 1857 was incorrectly synonymized by SMITH (1971) under I. albicosta but this species is, in fact, an older synonym of Ischnomyia spinosa Hendel, 1911 which is here transferred to the genus Arganthomyza Roháček, 2009 (see p. 66).

Ischnomyia albicosta strikingly resembles Arganthomyza vittipennis in wing pattern (cf. Figs 49 , 85 ). Because of this similarity these two species (the latter as Ischnomyia spinosa , junior synonym, see under Arganthomyza ) have formerly been grouped under the same genus Ischnomyia . However, these two species differ signincantly in other characters, including shape and structures of the head, pedal chaetotaxy, and, particularly, structures of the male and female terminalia; actually, the nearest relative of I. albicosta proved to be the East Palaearctic species I. barbarista (Roháček, 2009) , which has unpatterned hyaline wings. Ischnomyia barbarista was originally placed in Arganthomyza as the most aberrant member of this genus, forming a sister group to all other Arganthomyza species (see ROHÁĆEK & BARBER 2013) and leaving the genus somewhat heterogeneous because its close relationship to I. albicosta had not been recognized. Inasmuch as the clade with these two species is well supported by a number of autapomorphies, it is separated as a distinct monophyletic genus using the name Ischnomyia (see above under genus).

Ischnomyia albicosta differs from A. vittipennis in having an angular head with projecting frons, elongately ovoid eyes, entirely whitish yellow orbits, a very short frontal triangle, a mesonotum with 3 longitudinal orange yellow vittae, a much narrower dorsal dark band on the pleuron (covering only half of mesopleuron), a more strongly sinuate R 2+3, an additional longitudinal pale stripe between R 4+5 and M and very narrowly dark-bordered veins M and CuA 1, as well as further distinctive features in the male and female genitalia.

From its only congener, I. barbarista which has surprisingly similar male genitalia, I. albicosta can be easily distinguished by external characters and also by structures of the male and female terminalia (see description and above key).

Biology. We have very limited data on the biology of I. albicosta , which is derived almost exclusively from the only two localities where the junior author has ever encountered more than a single specimen of this species. Of note, both sites included collections of Arganthomyza vittipennis , although in lower numbers. One locality (Massachusetts: Farley – visited for less than an hour) was a small roadside site just above a river noodplain with scrubby canopy and an undergrowth somewhat reminiscent (though weedier) of several habitats in Ontario: Sault Ste. Marie yielding A. vittipennis ( I. albicosta does not occur that far north). The other site (Ontario: Burlington – Royal Botanical Gardens) was even more limited in that the productive area appeared to be restricted to a clump of vegetation growing in and around a wet depression in an open trail through mixed hardwood. Several visits were made to this site in 2002 and attempts to expand out from this focus were unsuccessful both along the trail and into the neighbouring shrubby and canopied habitat. The primary “hotspot” seemed to reduce to a patch of an unidentined sedge ( Carex sp.) that yielded good numbers of Anthomyza variegata (Loew) and Anthomyza dichroa sp. nov., both of which are often collected from Carex spp. elsewhere. This small habitat patch seems to have subsequently degraded, possibly from drought, and after several years a short visit in 2014 yielded only a single specimen of A. variegata . FOOTE (2002) reported a single specimen taken from Carex . Adults have been collected from 14 May (Georgia: Pine Mountain) to 27 August (Maryland: Plummers Island).

Distribution. This species is very seldom collected so its distribution is likely under-estimated here. It is a decidedly eastern species known from southern Ontario and Quebec in the northeast, southeast to Georgia and North Carolina and northwest to southern Minnesota and northwestern Wisconsin ( Canada: Ontario, Quebec; United States of America: District of Columbia, Georgia, Illinois, Indiana, Maryland, Massachusetts, Michigan, Minnesota, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, Wisconsin) (see Table 2, Fig. 597 ). Previously it was recorded from New Jersey ( ALDRICH 1905, MELANDER 1913), Pennsylvania ( OSTEN SACKEN 1878, ALDRICH 1905, MELANDER 1913, SABROSKY 1965), and Wisconsin ( MELANDER 1913, SABROSKY 1965), and SABROSKY’ S (1965) distributional range also explicitly references North Carolina and New York. The previously published record from New Jersey (see above) has not been connrmed by the material examined here but is likely based on a misidentincation of Arganthomyza vittipennis (previously Ischnomyia spinosa ) as listed below under that species.

Figures

Figs 47–49.Ischnomyia albicosta (Walker, 1849), male. 47 – head and anterior part of thorax, laterally; 48 – neotype laterally; 49 – wing, length 2.6 mm. Figs 47 and 49 based on specimens from Canada: Ontario. Photo by M. Deml (Fig. 47), J. Roháček (Fig. 48) and K. N. Barber (Fig. 49).

Figs 50–53. Ischnomyia albicosta (Walker, 1849), male (Canada: Ontario). 50 – abdomen, ventrally; 51 – f 1, posteriorly; 52 – external genitalia, caudally; 53 – the same, laterally. Scales = 0.3 mm (Fig. 50) and 0.1 mm (others). For abbreviations see p. 11.

Figs 54–59. Ischnomyia albicosta (Walker, 1849), male (Canada: Ontario). 54 – hypandrial complex, ventrally; 55 – transandrium, caudally; 56 – hypandrial complex, laterally; 57 – apex of nlum, subventrally; 58 – aedeagal complex, laterally; 59 – gonostylus, lateroventrocaudally (widest extension). Scales = 0.05 mm (Figs 57, 59) and 0.1 mm (others). For abbreviations see p. 11.

Figs 60–65. Ischnomyia albicosta (Walker, 1849), female (Canada: Ontario, Figs 60, 64; USA: Tennessee, Figs 61–63, 65). 60 – postabdomen, dorsally; 61 – spermathecae; 62 – female internal sclerites, ventrally; 63 – ventral receptacle, sublaterally; 64 – postabdomen, ventrally; 65 – female genital chamber and S8, laterally. Scales = 0.05 mm (Figs 61, 63) and 0.1 mm (others). For abbreviation see p. 11.

Figs 84–85.Wings of the Nearctic species of Arganthomyza. 84 – A. carbo Roháček & Barber, 2013, paratype male, wing length 2.8 mm; 85 – A. vittipennis (Walker, 1857), male, wing length 2.6 mm (both Canada: Ontario). Photo by K. N. Barber. Fig. 84 adapted from ROHÁĆEK & BARBER (2013: Fig. 166).

Fig. 597. Map of North America showing distributions of three members of Cluster 1: Ischnomyia albicosta (Walker, 1849), Anthomyza variegata (Loew, 1863), A. silvatica sp. nov. Anthomyza variegata and A. silvatica share a very dense, overlapping series of records (dots) in the Appalachian Mountains. See “Distributional patterns” for explanation of Clusters.