Ischnomyia Loew, 1863

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 : 41-44

Genus Ischnomyia Loew, 1863

Ischnomyia Loew,1863:325 [feminine]; OSTEN SACKEN (1878):198 (catalogue); WILLISTON (1896):105 (key); CZERNY (1902): 255 (redescription); ALDRICH (1905): 644 (catalogue); WILLISTON (1908): 80 (wing illustration), 298 (key); COQUILLETT (1910): 556 (catalogue); MELANDER (1913): 285, 292 (key); CURRAN (1934): 329 (key); STURTEVANT (1954): 557 (key); FREY (1958): 31 (key); CURRAN (1965): 329 (key); SABROSKY (1965): 819 (catalogue); COLE (1969): 435 (key); VOCKEROTH (1987): 75 (key); ARNETT (1993): 689 (list); ROHÁĆEK (1998a): 174 (checklist); ARNETT (2000): 896 (list); ROHÁĆEK (2009a): 106 (relationships).

Type species. Ischnomyia vittula Loew, 1863: 325 (monotypy) [= I. albicosta ( Walker, 1849) ].

Diagnosis. (1) Head distinctly longer than high, angular in pronle. (2) Eye large, subovoid, with longest diameter longitudinally oblique. (3) Frons moderately broad, anteriorly projecting in front of eye; (4) frontal triangle short (at most reaching to anterior two-nfths of frons), subshining to dull, microtomentose. (5) Frontal lunule small but always distinct. (6) Occiput distinctly concave. (7) Vertex with silvery microtomentose stripes lateral to ocellar triangle or orbits also with silver microtomentum. (8) Antenna geniculate, pedicel simple, 1st nagellomere strongly compressed laterally. (9) Arista densely to very densely (particularly basally) haired. (10) Palpus yellow, with 1 longer subapical seta and some ventral setulae. Cephalic chaetotaxy: (11) pvt relatively long, with apices crossed; (12) vti, oc and posterior ors longest of cephalic setae; (13) 3 ors but only 2 strong (middle ors shorter than posterior) with anterior ors reduced to setula; 1 microsetula in front of anterior ors; (14) postocular setulae short, in single row; (15) 1 long but slender vi, subvibrissa well developed (at least two-thirds of vi); (16) peristomal setulae small and sparse. (17) Posterior corner of head rounded. (18) Antenna and face with same colouring in both sexes.

(19) Thorax slightly narrower than head, subshining, despite microtomentum. Thoracic chaetotaxy: (20) 1 hu, 2 npl (anterior longer); (21) 1 long prs; (22) 1 long sa, 1 somewhat shorter pa; (23) 2 postsutural dc, both long and strong; (24) ac microsetae reduced, usually in only 2 medial rows, ending in front of level of posterior dc; (25) 2 sc (apical strong, laterobasal short and weak); (26) 1 minute upcurved ppl; (27) 2 distinct stpl (posterior somewhat longer) and a few setulae in dorsal half of sternopleuron. (28) Legs unicolourous yellow, at most distal half of apical tarsal segments somewhat darkened. (29) f 1 with short ctenidial spine; (30) t 2 with short ventroapical seta; (31) male f 3 with posteroventral row of setae that are short and thickened distally. (32) Wing relatively long and narrow; (33) wing membrane unicolourous or with brown and whitish hyaline longitudinal pattern. (34) C with distinct spinulae among nne hairs on Cs 2; (35) R 2+3 long, sinuate to subparallel to C, ending farther from apex of R 4+5 than R 4+5 ends from apex of M; (36) R 4+5 slightly bent (recurved) and somewhat converging with M apically; (37) cell dm moderately long and rather narrow; cross-vein r-m situated in front of middle of cell dm; (38) distal part of CuA 1 longer than dm-cu, reaching (with its colourless end only) wing margin, A 1 ending far from it. (39) Anal lobe and alula small, the latter narrow.

Male abdomen. (40) T1 separate from T2, only laterally fused; (41) T2–T5 large and broad, all uniformly dark-pigmented. (42) S2–S5 narrow, brown or (secondarily) pale-pigmented. Male postabdomen: (43) T6 short, transverse, bare, pale brown laterally, unpigmented medially. (44) S6 and S7 strongly asymmetrical, partly fused and situated laterally, S6 with 2–4, S7 with 2 setulae. (45) S8 relatively long, less asymmetrical, setose on posterior half.

Male genitalia. (46) Epandrium medium-sized, somewhat wider than high, with a number of setae, 2 pairs of setae distinctly longer. (47) Anal nssure medium-sized, relatively broadly rounded, triangular. (48) Medandrium relatively broad, widened ventrally, with dorsal corners slightly projecting, without setae. (49) Cercus relatively large but weakly sclerotized and pale-pigmented, with pale setae. (50) Gonostylus simple, medium-sized (shorter and paler than epandrium), with 2 denticles on apex, micropubescent externally and setose internally. (51) Hypandrium medium-sized, with anterior nat lobes reduced, incurved and fused with anterior part of postgonites; (52) transandrium with a very distinctive, forked caudal process, having its distal arms anteroventrally projecting and dilated. (53) Pregonite low, nat, fused to hypandrium, with small but distinct posterior lobe and 2 (anterior and posterior) groups of setae. (54) Postgonite simple, slender, relatively straight to slightly S-shaped, without distinct setula. (55) Phallapodeme robust, with large bicuspidate apex, basally broad fulcrum and shortly bifurcate base. (56) Phallophore short, simple, without ventral process; (57) distiphallus composed of distally membranous saccus and slender sclerotized nlum. (58) Saccus with medium-sized to small membranous part, sclerotized narrower proximal part and provided with several larger cup-like tubercles, otherwise unarmed; (59) nlum short, formed by 2 broad, closely attached to partly fused ribbon-like sclerites, ventral shorter and dilated, dorsal longer, attenuated and ending in membranous but nnely spinulose and denticulate apex. (60) Aedeagal part of folding apparatus with slender, weakly sclerotized but spinulose connecting sclerite and its external wall with relatively robust, dark and dense lenticular to tooth-like excrescences. (61) Basal membrane below caudal process with dense and dark spine-like tubercles. (62) Ejacapodeme relatively long, with dark clubbed projection medially.

(63) Female abdomen relatively shining, with broader terga (T2–T6) and narrower sterna (S2–S5). (64) Postabdomen relatively short and wide, basally broad, caudally tapered, telescopically retractable, with all terga dark-pigmented. (65) T6 very large and broad, S6 relatively small, much narrower but transverse. (66) T7 and S7 either fused to form synsclerite T7+S7 with pale sternal part, or separate, with S7 large and dark, and pleural membrane between T7 and S7 very narrow, reduced. (67) T8 simple, nat, all dark-pigmented or with pale margins; (68) S8 relatively short, medially longitudinally divided, with posterior bare parts dorsally recurved and invaginated into 8th segment. (69) Internal structures of female genital chamber (uterus) formed by several fused anterior sclerites (situated unusually distally in female genital chamber) and by (70) 1 posterior, elongate, very nne, pale or unpigmented annular sclerite. (71) Ventral receptacle hyaline, elongate and slender, with weakly sclerotized and ringed distal end bent apically and either conical or projecting. (72) Accessory glands very small, on distally dilated and partly ringed ducts. (73) Spermathecae (1+1) broadly ovoid, each with nnely ringed surface, plain basal part with minute spinulae, small terminal invagination, eccentric duct insertion and short cervix; spermathecal duct very long. (74) T10 small and transverse, brownish, sparsely microtomentose and with 1 pair of very long setae; (75) S10 larger than T10, rounded triangular, micropubescent, with long nne setae at posterior margin. (76) Cercus relatively short, with a number of nne setae, apical and dorsopreapical longest.

Discussion. A thorough revision of both species formerly assigned to the genus Ischnomyia Loew, 1863 , viz. I. albicosta ( Walker, 1849) and I. spinosa Hendel, 1911 and its synonyms revealed that these two species are not closely related in spite of their surprisingly similar wing pattern. Ischnomyia albicosta (the type species of Ischnomyia ) proved to be the nearest relative of the East Palaearctic Arganthomyza barbarista Roháček, 2009 (the most enigmatic species of Arganthomyza ), while I. spinosa (which has an older synonym, viz. Arganthomyza vittipennis ) is most closely allied to species of the clade A. duplex group + A. socculata group of the genus Arganthomyza (as denned by ROHÁĆEK & BARBER 2013). Because the afnliation of A. barbarista with Arganthomyza causes distinct heterogeneity of this genus (for its relationships see ROHÁĆEK & BARBER 2013: Fig. 173 ), this species is here transferred to the genus Ischnomyia as Ischnomyia barbarista (Roháček, 2009) comb. nov. and I. spinosa Hendel, 1911 is transferred to the genus Arganthomyza Roháček, 2009 under its older name, thus as Arganthomyza vittipennis ( Walker, 1857) comb. nov., see below.

These systematic actions however necessitate redennitions of taxonomic limits of both involved genera. The genus Ischnomyia is redescribed above. It is postulated as sister group of the genus Arganthomyza . Both these genera share the following synapomorphies (numbered as in above diagnosis): (7) vertex (top of head) with silvery microtomentose spots or stripes between frontal triangle and posterior part of orbits; (24) ac microsetae in reduced number, at most in 2 rows, sometimes entirely absent; (49) male cercus relatively large but weakly sclerotized and pale-pigmented; (58) saccus with reduced armature, with only some blunt tubercles; (59) nlum short and robust, formed by two broad closely appressed to partly or completely fused sclerites terminating in somewhat dilated and nnely spinulose or denticulate apex; (64) female postabdomen relatively short; (66) female T7 and S7 normally forming complete tergosternal ring (in some species with S7 secondarily separate); (69) annular sclerite in the female genital chamber elongate; (74) female T10 small, dark and transverse, markedly shorter than S10 and with a pair of very long medial setae.

The genus Ischnomyia is best characterized (in contrast to Arganthomyza ) in having (1) head longer than high and angular in pronle, (2) eye with longest diameter longitudinally oblique, (4) frontal triangle short, (9) arista densely to very densely (particularly basally) haired, (29) f 1 with ctenidial spine shortened, (50) gonostylus with 2 denticles on apex, (52) transandrium with a distinctively forked caudal process having its arms anteroventrally projecting and dilated, (54) postgonite without distinct setula, (55) phallapodeme robust, with large apex and broad fulcrum at base, (58) saccus with a few larger, pigmented, cup-like tubercles, (60) aedeagal part of folding apparatus provided with relatively robust, dark excrescences, (61) basal membrane with dense dark spine-like tubercles, (64) female postabdomen with all terga dark-pigmented, (69) female genital chamber with several fused anterior sclerites situated unusually distally (far from genital opening), (73) spermatheca with eccentric duct insertion and spermathecal duct very long. Most of these characters are apomorphic compared to Arganthomyza (1, 2, 9, 29, 50, 52, 54, 58, 60, 61, 69); the eccentric insertion of the spermathecal duct is probably apomorphic although the long duct is obviously a plesiomorphic character state. In conclusion, Ischnomyia , as delimited above, seems to be a distinct group, the monophyly of which is well supported.

The parallel evolution of highly similar wing ornamentation in three lineages, i.e. in one species of Ischnomyia ( I. albicosta ), one species of Arganthomyza ( A. vittipennis ) and two species of the East Palaearctic genus Epischnomyia (see ROHÁĆEK 2006a, 2009a), certainly is an interesting phenomenon. An observation worth mentioning is that at one site (Ontario: Sault Ste. Marie – Baseline Rd.), A. vittipennis was found along with the leafhopper, Eupteryx ssavoscuta Gillette, 1898 (Cicadellidae) , which has a strikingly similar wing pattern. The two patterns share a medial longitudinal dark band that abruptly widens apically ( Fig. 88 ). The hosts of E. ssavoscuta are ferns which we have suspected might be implicated as hosts for some woodland Arganthomyza and Anthomyza species. No other species of Anthomyzidae sharing these habitats has such a pattern and these ferns are lacking in some sites where A. vittipennis is present (e.g. Ontario: Moosonee). The two sites where I. albicosta has been collected by the junior author (see Biology under I. albicosta below) have also yielded A. vittipennis but ferns were a noticeable component only at Massachusetts: Farley and the presence of E. ssavoscuta was not noted. Though aposematism and an associated mimicry may be operating here, we suggest that this represents a more generalized example of disruptive colouration. This wing pattern may make the differentiation between anterior and posterior ends of the animal more difncult for predators, possibly reducing the rate of successful attacks. A similar gross body silhouette and colouration is shared between some Stiphrosoma species and nymphs of certain fulgoroid planthoppers ( Hemiptera ) (K. N. Barber, unpublished) associated with the thatch below graminoids.

Two species included: Ischnomyia albicosta ( Walker, 1849) and I. barbarista (Roháček, 2009) that are widely separated on different continents – I. albicosta in the eastern Nearctic and I. barbarista in the East Palaearctic ( ROHÁĆEK 2009a, as Arganthomyza ).

Key to identincation of Ischnomyia species (world)

1 Wing longitudinally brown-banded ( Fig. 49 ).Arista relatively sparsely haired ( Fig. 48 ). Frons with broad medial longitudinal band dull blackish brown. Mesonotum brown to blackish brown, with 3 narrow orange yellow vittae between dorsocentral lines ( Fig. 48 ). Preabdominal sterna brown. Male S5 brown, with large posteromedial subtriangular area unpigmented and distinctively micropubescent ( Fig. 50 ). Saccus more slender; ejacapodeme with long projection ( Fig. 58 ); apex of nlum with a few denticles ( Fig. 57 ). Female T7 and T8 longer ( Fig. 60 ); S7 separate, large and brown-pigmented ( Fig. 64 ). Distal end of ventral receptacle shortly conical ( Fig. 63 ); spermathecae shortly oval, basally with reduced spinulae and its terminal impression shallow ( Fig. 61 ). ..... ................................................................. I. albicosta ( Walker, 1849) ( Canada, USA)

– Wing with unicolourous hyaline membrane ( ROHÁĆEK 2009a: Fig. 88 ). Arista very densely (particularly in basal third) hirsute ( ROHÁĆEK 2009a: Fig. 73 ). Frons largely yellow to orange, only ocellar triangle brown. Mesonotum largely yellow, only brownish lateral to dc lines ( ROHÁĆEK 2009a: Fig. 73 ). Preabdominal sterna pale ochreous. Male S5 simple, entirely pale-pigmented. Saccus more voluminous, dilated distally; ejacapodeme with short projection ( ROHÁĆEK 2009a: Fig. 79 ); apex of nlum with more denticles ( ROHÁĆEK 2009a: Fig. 80 ). Female T7 and T8 shorter ( ROHÁĆEK 2009a: Fig. 81); S7 pale ochreous and coalesced with T8 ( ROHÁĆEK 2009a: Fig. 84 ). Distal end of ventral receptacle longer conical with apex curved ( ROHÁĆEK 2009a: Fig. 83 ); spermathecae longer, ovoid, basally with numerous spinulae and its terminal invagination conical ( ROHÁĆEK 2009a: Figs 82 , 87 ). ........................................................................... ............................................. I. barbarista (Roháček, 2009) ( Korea, Russia: Far East)

Figures

Figs 168–175. Arganthomyza disjuncta Roháček & Barber, 2013, paratype male (Canada:Alberta). 168 – external genitalia, caudally; 169 – base of phallapodeme, dorsally; 170 – external genitalia, laterally; 171 – hypandrial complex, laterally; 172 – transandrium, caudally; 173 – apex of nlum of distiphallus, anteroventrally (widest extension); 174 – aedeagal complex, laterally; 175 – gonostylus, lateroventrally (widest extension). Scales = 0.05 mm (Figs 173, 175) and 0.1 mm (others). Adapted from ROHÁĆEK & BARBER (2013: Figs 122–128).

Figs 86–89. Arganthomyza vittipennis (Walker, 1857). 86 – A. vittipennis, lectotype female, laterally; 87 – holotype female of Ischnomyia spinosa Hendel, 1911, laterally; 88 – living male of A. vittipennis on a leaf, body length ca. 2.8 mm; 89 – head and anterior part of thorax of male (both from Canada: Ontario: Sault Ste. Marie). Photo by J. Roháček (Figs 86–88) and M. Deml (Fig. 89).

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 70–76. Arganthomyza carbo Roháček & Barber, 2013, paratype male (Canada: Ontario). 70 – external genitalia, caudally; 71 – the same, laterally; 72 – hypandrial complex, laterally; 73 – transandrium, caudally; 74 – apex of nlum of distiphallus, anteroventrally (widest extension); 75 – aedeagal complex, laterally; 76 – gonostylus, ventrolaterally (widest extension). Scales = 0.1 mm. Adapted from ROHÁĆEK & BARBER (2013: Figs 53–59).

Figs 77–83. Arganthomyza carbo Roháček & Barber, 2013, paratype female (Canada: Ontario). 77 – ventral receptacle, laterally; 78 – postabdomen, dorsally; 79 – the same, ventrally; 80 – apex of postabdomen and female genital chamber, laterally; 81 – spermathecae; 82 – internal sclerites, ventrally; 83 – the same, laterally. Scales = 0.2 mm (Figs 78, 79), 0.1 mm (Fig. 80) and 0.05 mm (others). Adapted from ROHÁĆEK & BARBER (2013: Figs 60–66).

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).