Arganthomyza socculata ( Zetterstedt, 1847 )

Roháček, Jindřich & Barber, Kevin N., 2013, A worldwide review of the genus Arganthomyza Roháček, with revision of the Nearctic species (Diptera: Anthomyzidae), Zootaxa 3604 (1), pp. 1-72 : 38-41

Arganthomyza socculata ( Zetterstedt, 1847)

Figures 8 , 137–165 , 171, 172

Geomyza socculata Zetterstedt, 1847: 2534 .

Anthomyza socculata: Andersson 1976: 50–51 (redescription); Soós, 1981: 111 (key); Andersson 1984: 53 (catalogue); Roháček, 1984: 393 (key), 1987: 55–57 (diagnosis), 1998: 173 (world checklist); 2006: 191–196 (redescription and synonymy).

Arganthomyza socculata: Roháček, 2009: 63 , 74 (key, generic combination).

Anthomyza ungulata Loew, 1873: 301 ; Czerny, 1902: 252; 1928: 5; Collin, 1944: 267 (key); Trojan, 1962: 39; Stackelberg, 1970: 326 (key); Andersson 1984: 53 (catalogue); Roháček 1984: 392 (synonymy).

Type material: Geomyza socculata Zetterstedt : Holotype ♂ labelled: “ G. socculata ♂. Ostrog. Stenh.”, “ Lectotypus Geomyza socculata Zett. , design. 1974 H. Andersson ” [red label], “1969, 925” [green label], “Type No. 2095:1, Zool. Mus. Lund Sweden, Anthomyzidae ”, “ Holotypus ♂ Geomyza socculata Zett., J. Roháček des. 2005” [red label] and “ Anthomyza socculata (Zett., 1847) ♂, J. Roháček det. 2005” ( MZLU, genit. prep., examined). This type specimen was incorrectly designated as lectotype by Andersson (1976: 45) but it is a holotype because only this male from Östergötland: Häradshammar , collected by Stenhammar, was listed in the original description.

Anthomyza ungulata Loew : Lectotype ♂ (designated by Roháček 1984: 392) labelled: “Kultuk, v. Maak”, “ Coll. H. Loew ”, “ Anthomyza ungulata Lw ” (Loew’s handwriting), “Type” [orange-red label], “Zool. Mus. Berlin ” [yellow label], “ Lectotypus, Anthomyza ungulata Loew ♂, J. Roháček des. 1983” [label with red margin and the word “ Lectotypus ”] and “ Anthomyza socculata (Zett.) ♂, J. Roháček det. 1983”. The specimen is in good condition ( ZMHB, genit. prep., examined). Paralectotypes: with the same labels as the lectotype except for Loew’s determination label, 2♀ ( ZMHB, examined).

Other material examined: for Palaearctic specimens (311♂ 232♀) see Roháček (2006, 2009). Nearctic Region: UNITED STATES: Alaska: Cold Bay, Trout Creek , 163°W, on tundra, 21.viii. 1952, 1♂, W. R. Mason leg. ( CNCI, genit. prep.); Kenai , Kenai Peninsula , 23.vii.1978, 1♀, P. H. Arnaud, Jr. leg. ( CASC, genit. prep.); Kenai , Lowell Point , 6.5 km S Seward, 60°03.9’N, 149°26.6’W, 31.vii.2003, 1♂, D. & W. N. Mathis leg. ( USNM ENT 00200089 , genit. prep.); King Salmon, Naknek R., 11.vii.1952, 1♂ 1♀, W. R. Mason leg. ( CNCI, both genit. prep.); Knik Lake , NW of Wasilla, sweeping vegetation edge of lake, 18.vii.1978, 1♀, P. H. Arnaud, Jr. leg. ( CASC, genit. prep.); Mat-Su, Talkeetna, Susitna River , 62°19.4’N 150°07.2’W, 4.viii.2003, 3♂, D. & W. N. Mathis leg. ( USNM ENT 00201107-09 , all genit. prep.); Palmer, Agricultural Experiment Station , Glenn Highway A-42, 30.vii.1978, 5♂ 3♀, P. H. Arnaud, Jr. leg. ( CASC, 4♂ 3♀ genit. prep.); Unalakleet, 15.vi.1961, 1♀, 22.vi.1961, 1♀, 27.vi.1961, 1♂ (genit. prep.), 30.vi.1961, 1♂ 1♀ (1♂ genit. prep.), 3.vii.1961, 1♂ 1♀ (1♂ genit. prep.), 4.vii.1961, 5♂ 1♀ (1♂ wing removed, all genit. prep.), 8.vii.1961, 1♀, 10.vii.1961, 2♀, B. S. Heming (all CNCI) ; Unalakleet , 18.vi.1961, 7♂ 7♀ (5♂ 5♀ CNCI, 1♂ wing removed, 1♂ headless, 1♀ missing head, some legs, abdomen, 5♂ 2♀ genit. prep., 2♂ 2♀ DEBU, 2♂ 1♀ genit. prep.), 19.vi.1961, 1♂ 4♀ (1♂ 1♀ genit. prep.), 29.vi.1961, 1♀, 3.vii.1961, 3♂ 6♀ (3♂ 3♀ genit. prep.), 5.vii.1961, 2♀ (1♀ genit. prep.) (all CNCI) , 6.vii.1961, 3♂ 5♀ (1♂ 3♀ CNCI, 1♂ genit. prep., headless, 2♂ 2♀ SMOC, all genit. prep.), 8.vii.1961, 2♂ 1♀ (all genit. prep., 1♂ headless), 13.vii.1961, 1♀, 7.viii.1961, 1♀, R. Madge leg (all CNCI) .

Redescription: M a l e. Total body length 1.90–2.42 mm; general colour brown to blackish brown, distinctly though rather sparsely pale grey microtomentose and relatively shining. Head somewhat higher than long, rounded anteriorly in profile. Occiput dorsomedially slightly concave, dark brown and shining. Frons with anterior half dull yellow (often with yellow extended along sides of frontal triangle more posteriorly), frontal and ocellar triangles dark brown, subshining; orbits anteriorly yellow and silvery white microtomentose and with subshining (less microtomentose) brown stripe behind posterior ors; distinctive silvery microtomentose area between the latter stripe and frontal triangle well developed. Frontal triangle reaching up to anterior third of frons and its anterior tip often pale brown to ochreous-yellow. Frontal lunule small but visible, yellow. Face narrow, medially weakly sclerotized and folded, and like parafacialia and gena, light yellow to white with silvery white microtomentum; postgena ventrally yellow, dorsally brown, sparsely microtomentose; mouthparts light yellow. Cephalic chaetotaxy: pvt small, but usually crossed; vti longest of cephalic setae; oc very slightly shorter than vti; vte and posterior ors slightly to distinctly shorter than vti; 2 long ors, anterior slightly to distinctly (sometimes half length only) shorter than posterior; 1–2 microsetulae in front of the anterior ors; 1–3 pairs of medial microsetulae in the anterior third of frons; 1 small setula behind vte; postocular setulae relatively long and sparse (6–7), in single row; postgena with several setulae and 2–3 posteroventral setae; 1 long vi (slightly longer than anterior ors), subvibrissa weak but longer than peristomal setulae (up to two-thirds of vi); 5–8 fine peristomal setulae. Palpus slender, yellow, with 1 dark ventral preapical seta and several (4–6) paler ventral setulae. Eye large, suboval, with longest diameter slightly oblique and 1.4–1.5 times as long as shortest. Smallest genal height about 0.10 times as long as shortest eye diameter. Antenna geniculate, entirely yellow; 1st flagellomere with relatively short white pilosity. Arista dark brown, with paler basal segment, 1.8–1.9 times as long as antenna, with yet shorter cilia than 1st flagellomere.

Thorax very slightly narrower than head, entirely dark brown and relatively shining despite sparse pale grey microtomentum. Mesonotum with reduced number of microsetae but macrosetae long. Thoracic chaetotaxy: 1 hu (only as long as anterior npl); 2 npl (anterior much longer than posterior); 1 long prs (longer than anterior npl); 1 long sa (as long as prs); 1 pa (shorter than prs); 2 long postsutural dc (posterior very long, anterior shorter but usually slightly longer than prs) and 4–6 dc microsetae in front of them, the hindmost often enlarged; ac microsetae in 2 rows and represented by only 1–3 (often incomplete) pairs between dc, none posteriorly; 2 sc, laterobasal shorter than anterior dc, apical as long as posterior dc; 1 unusually long but very weak and pale ppl; 2 relatively strong stpl, anterior usually shorter and weaker, and 2–3 setulae in dorsal half of sternopleuron similar to those on mid coxa, its ventral part with 3 longer pale setae. Scutellum rounded triangular, convex dorsally. Legs light yellow, only larger distal part of apical tarsal segments dark to blackish brown and sharply contrasting with rest of tarsi. f 1 with ctenidial spine slightly longer than maximum width of t 1 and with usual long setae in posteroventral and posterodorsal row. f 3 with a row of sparse posteroventral setae, distal 6–7 of which shorter and somewhat thicker; t 2 with relatively short ventroapical seta; mid and hind basitarsi sometimes with slightly enlarged but not thickened proximoventral setula ( Fig. 8 ). f 2, t 1, t 3 and and rest of tarsi simply setulose. Wing ( Figs 171, 172 ) only slightly longer than body length (of air-dried specimens) and not very narrow, with pale ochreous veins and membrane. C with very small but relatively dense spinulae between apices of R 1 and R 2+3. R 2+3 long, bent parallel to C with apex almost straight; R 4+5 very slightly bent (recurved) and running parallel with M apically. Discal (dm) cell moderate or relatively short, with r-m situated at or slightly in front of the middle of dm cell. Apical portion of CuA 1 usually longer than dm-cu, almost reaching wing margin; A 1 short, ending far from it. Alula small but relatively broad. Wing measurements: length 1.94–2.56 mm, width 0.65–0.85 mm, Cs 3: Cs 4 = 0.97–1.32, rm\dmcu: dm-cu = 1.76–2.87. Haltere light yellow, stem basally darker yellow.

Abdomen with all terga dark brown and sterna brown, sparsely grey microtomentose, and relatively shining. T1 and T2 almost separate, only laterally fused. T3–T5 subequal, broad, bent onto ventral side of abdomen. Preabdominal sterna relatively large, becoming larger posteriorly; S2–S4 slightly transverse to almost as long as wide; S1 shorter and strongly transverse, bare and with darker posterior marginal stripe; S5 largest, broad, transversely trapezoidal, sometimes posteriorly slightly emarginate. T6 very short, transversely band-like, bare, brown but medially narrowly desclerotized and unpigmented. S6 (shorter) and S7 strongly asymmetrical, both with strongly sclerotized and darker anterior margin, each usually with 2 setulae; S8 very long (longer than epandrium), tapered posteriorly, with sparse setae in posterior half or two-thirds.

Genitalia. Epandrium ( Figs 138, 139 , 145, 146 ) dark brown, relatively short, moderately broad and setose, with 1 dorsolateral pair of long and thicker setae; anal fissure dorsally relatively small, rounded subtriangular. Cercus relatively long, densely setose, apical seta not longer than others. Medandrium ( Figs 138 , 145 ) high, ventrally broadly incised (copying the shape of anal fissure), dorsally tapered, dorsolateral corners slightly projecting. Gonostylus ( Figs 138, 139, 144–146, 151 ) ochreous to yellow, flat, slightly bent medially, of elongately subtriangular shape, with tapered but rounded apex, largely micropubescent on outer side and setose mostly on inner side; its shape variable: in Nearctic and E. Palaearctic specimens more slender and apically more acute (see Fig. 144 ) on average than in European specimens ( Fig. 151 ) but always with anterior margin convex and posterior concave (in largest extension view). Hypandrium ( Figs 140 , 147 ) relatively robust, with anterior internal lobes small, ventrally (anterior to pregonite) more distinctly excavated than in A. disjuncta sp. n.; posterior wide parts of hypandrium fused with transandrium. Transandrium ( Figs 141 , 148 ) simple, band-like, dorsally dark-pigmented, with caudal process inconspicuous (reduced), only indicated by a pair of weakly sclerotized strips reaching to basal membrane. Pregonite ( Figs 140 , 147 ) fused to hypandrium, low, slightly projecting, with 2–3 posterior (1–2 longer on a tubercle-like process) and 3 anterior (all internal) setae. Postgonite ( Figs 140 , 147 ) pale, elongate, with blunt apex having weakly sclerotized (and rather variable) terminal dilation, 1 anterior setula (in proximal fourth to third) and several granular sensilla on surface. Basal membrane ( Figs 141 , 148 ) with pale transverse spine-like excrescences. Aedeagal part of folding apparatus with dark granulose tubercles on proximal part (covering larger area on right side than on left) and usual fine striae. Connecting sclerite slender, of subgranulose structure ( Figs 143 , 150 ). Phallapodeme slender, with basal part narrowly and rather shortly forked ( Fig. 137 ), and apex shortly (often rounded) bicuspidate. Aedeagus with short, frame-like phallophore ( Figs 143 , 150 ) and large distiphallus basally reinforced by elongate sclerites. Saccus relatively short, proximally weakly sclerotized, and its membranous distal part with rounded hyaline tubercles, those on apex provided with minute spinulae. Filum formed by single bent ribbon-like sclerite, pale-pigmented; its flat apex dilated and mostly membranous, provided with several small teeth and some micropubescence and/or microspinulae ( Figs 142 and 149 are from different views). Ejacapodeme well developed, with slender digitiform projection.

F e m a l e. Similar to male unless mentioned otherwise. Total body length 1.98–2.94 mm. Mouthparts usually darker yellow to ochreous. f1 with ctenidial spine somewhat longer; f3 posteroventrally simply setulose. Wing measurements: length 2.18–2.90 mm, width 0.75–0.99 mm, Cs 3: Cs 4 = 0.96–1.29, rm\dm-cu: dm-cu = 1.72–3.79. Discal (dm) cell longer and narrower on average. Abdomen with preabdominal sclerites distinctly short and more transverse. T2 narrower than T3–T5, the latter subequal in size, all sparsely setose. Preabdominal sterna somewhat narrower than in male, brown to pale brown, finely setose. S1 transverse, bare, with posterior transverse stripe; S2 darker brownish than other sterna; S2–S5 becoming wider posteriorly, S5 largest, slightly wider than long (but narrower and always lighter than S6).

Postabdomen ( Figs 153, 158 , 161, 165 ) relatively short and wide. T6 large, broad (broader in European specimens— Fig. 161 ), with paler posterior margin. S6 transverse, broader than S5, dark and often with paler posterior margin as in T6. T7 and S7 completely fused into dark brown ring-shaped tergosternum, dorsally in Nearctic and E. Palaearctic often with distinctly paler posterior and sometimes also anterior band ( Fig. 153 ), ventrally usually with dark, transverse anteromedial stripe ( Figs 158 , 165 ) which can also be sometimes reduced and with long setae at posterior margin. Anterior margin of original S7 sometimes with a pair of small appendages (cf. Fig. 158 ). 8th segment partly membranous and densely micropubescent. T8 plate-shaped, dark except for posterior margin, wider and anteriorly less tapered in European ( Fig. 161 ) than in Nearctic ( Fig. 153 ) specimens. S8 much shorter than T8, medially divided to form 2 finely setose sclerites being recurved and deeply invaginated (see Figs 154, 158 , 162 ). Genital chamber (uterus) slender, with internal sclerotization ( Figs 154–156 , 162–164 ) formed by 1 pair of relatively simple, flat but curved sclerites and 1 elongate, narrow and (particularly posteriorly) curved annular sclerite lying below them. Ventral receptacle ( Figs 159 , 164 ) hyaline, slender, long, strongly curved, gradually tapering towards blunt apex (obviously somewhat thicker and shorter in Nearctic specimens); accessory gland hyaline, with some grains on surface, on slender more or less ringed duct. Spermathecae (1+1) shortpyriform, with dark transversely striated surface and slender base provided with rosette of 5–6 characteristic bellshaped appendages (see Figs 152, 157 , 160 ) some of which can have doubled apex in Nearctic specimens ( Fig. 152 ); cervix short and pale-pigmented; duct of spermatheca broad and short ( Figs 156 , 164 ). T10 small, transverse, dark, with distinctive micropubescence and 1 pair of very long (longer in Nearctic specimens, Fig. 154 ) medial setae. S10 larger than T10, roughly pentagonal, micropubescent and finely setulose. Cercus relatively short and robust, with fine setae, apical and dorsopreapical being longest ( Figs 154 , 162 ).

Variability: This widespread Holarctic species displays remarkable variability in the postabdominal characters (cf. Figs 153–159 , 160–165 ). The Nearctic specimens closely resemble those from eastern Asia ( Mongolia, Russia: Far East) and compared to European specimens they seem to be generally smaller, with the male gonostylus narrower and more acute, the female T7+S7 often anteriorly and/or posteriorly pale-margined, the female T8 narrower, the ventral receptacle thicker, and the spermathecae often with doubled bell-shaped appendages.

Discussion: Arganthomyza socculata ( Zetterstedt, 1847) is very closely allied to A. disjuncta sp. n. and forms with it a distinctive sister pair distinguished by the following apomorphies (see Fig. 173 ): peculiar bell-shaped appendages on spermathecae (character 24); filum of distiphallus with single sclerite (i.e. two original sclerites completely fused, character 13, state 3); apex of filum finely spinulose (character 15). Arganthomyza socculata and A. disjuncta sp. n. are distinct in the female sex but their males are very similar even in the genitalic structures (for differences see the key and in the description and discussion under A. disjuncta sp. n.).

The geographical variability discussed above, particularly the differences between European and E. Palaearctic + Nearctic specimens, will need future study to evaluate the differences between the populations in these areas. Molecular studies may help to elucidate this problem, but for the time being these populations are considered conspecific. However, we do not rule out the possibility that the Nearctic populations of A. socculata (hitherto known only from Alaska) interbreed in Alaska with the sympatric and closely allied A. disjuncta , because a few males found in some localities there could not be assigned to one or the other species. However, we cannot be sure that A. socculata is really restricted to Alaska in North America because most of the boreal areas of the Nearctic Region have not been sufficiently sampled for Diptera .

Biology: In northern Europe ( Andersson 1976) A. socculata occurs rather frequently in dry meadows, grassy habitats along roadsides, in gardens and even in grazed fields. In Central Europe ( Roháček 2006), by contrast, it seems to be restricted to mountains (usually above 1000 m, up to 2500 m in the Alps), living rather locally in montane and alpine meadows, usually in tufts of larger grasses on creek shores. In Central and East Asia ( Kirghizia, Russia, Mongolia), A. socculata is among the commonest anthomyzid flies found in montane ranges (up to 2500 m) where it is associated with grassland (often grazed) habitats near rivers and other water bodies. In Kamchatka it was swept abundantly from the grassy undergrowth of a birch forest ( Roháček 2006). Host plants of A. socculata have hitherto not been determined (no rearing record). Besides unidentified Poaceae ( Andersson 1976; Roháček 2006, 2009), the species was also collected in Cyperaceae ( Eriophorum angustifolium Honck , see Krogerus 1960) but it is not known if it can develop in them. Unfortunately no data on the habitat and/or plant association are available for the Nearctic (Alaska) specimens, except for one specimen swept in tundra and one from vegetation on the edge of a lake. The habitat is nonetheless assumed to be similar to that of A. disjuncta sp. n. (see above) at least in Alaska where the two species co-occur at a few sites. Adults were recorded here in June to August (i.e. 15.vi. to 4.viii., possibly reflecting its northerly restriction to Alaska) as are those from the Palaearctic Region ( Roháček 2006).

Distribution: A Boreo-alpine species widespread in the northern belt of the Palaearctic Region ranging from Iceland to Kamchatka but also occurring in montane ranges of more southern latitudes. Its Palaearctic distribution is summarized by Roháček (2006, 2009) as follows: Austria, Czech Republic ( Bohemia), Estonia, Finland, Great Britain ( Scotland), Iceland, Kazakhstan, Kirghizia, Lithuania, Mongolia, North Korea, Norway, Poland, Russia (Central and North European Territory, W. and E. Siberia, Far East), Slovakia, Sweden, Switzerland, Ukraine. It is here recorded for the first time from the Nearctic Region but as yet only from Alaska ( United States).

Arganthomyza socculata / disjuncta

List of male specimens not distinctly referable to either of the two species:

UNITED STATES: Alaska: Kenai, Homer Spit, 59°38’N 151°29.8’W, 2.viii.2002, 1♂, D. & W. N. Mathis leg. ( USNM ENT 00182722 , genit. prep.); Mat-Su, Talkeetna, Susitna River , 62°19.4’N 150°07.2’W, 4.viii.2003, 2♂, D. & W. N. Mathis leg. ( USNM ENT 00201110 , -11, both genit. prep.); Palmer, jeep trap, 13.vii.1961, 2♂, K. Sommerman leg. ( USNM, both genit. prep.); Unalakleet, 3.vii.1961, 1♂, 4.vii.1961, 1♂, B. S. Heming leg., 18.vi.1961, 2♂, 6.vii.1961, 1♂, R. Madge leg. (all CNCI, all genit. prep.) .

Figures

FIGURE 173. One of two most parsimonious trees (L = 42 steps, CI = 0.80, RI = 0.81) chosen to represent the phylogeny of Arganthomyza species. Ambiguous characters (08, 13, 14, 18, 21, 29) are optimized using the fast (ACCTRAN) method. Full circles = non-homoplasious character states, empty circles = homoplasious character states. Numbers above branches agree with character numbering, those below branches indicate apomorphic (1, 2, 3) or plesiomorphic (0) states of characters. E PA = East Palaearctic, HO = Holarctic, NA = Nearctic, OR = Oriental, PA = Palaearctic.

FIGURES 7–11. Species of Arganthomyza. 7, 9—A. setiplanta (Roháček), apex of t2 and basitarsus, anterior (7) and fore femur, posterior (9) (female holotype). 8—A. socculata (Zetterstedt), apex of t2 tibia and basitarsus, anterior (female, Russia: Baikal area). 10—A. barbarista Roháček, general habitus, lateral (male holotype). 11—A. versitheca Roháček, head, dorsal (male paratype). Scales: Fig. 10 = 0.5 mm, others = 0.2 mm. Figs 7–9 adapted from Roháček (1987), Figs 10, 11 adapted from Roháček (2009). For abbreviation see text.

FIGURES 137–144. Arganthomyza socculata (Zetterstedt) (male, USA: Alaska). 137—base of phallapodeme, dorsal. 138—external genitalia, caudal. 139—ditto, lateral. 140—hypandrial complex, lateral. 141—transandrium, caudal. 142—apex of filum of distiphallus, ventral (widest extension). 143—aedeagal complex, lateral. 144—gonostylus, lateroventral (widest extension). Scales: Figs 142, 144 = 0.05 mm, others = 0.1 mm.

FIGURES 145–151. Arganthomyza socculata (Zetterstedt) (male, Sweden). 145—external genitalia, caudal. 146—ditto, lateral. 147—hypandrial complex, lateral. 148—transandrium, caudal. 149—apex of filum of distiphallus, subventral (widest extension). 150—aedeagal complex, lateral. 151—gonostylus, lateroventral (widest extension). Scales: Figs 149, 151 = 0.05 mm, others = 0.1 mm. Adapted from Roháček (2006).

FIGURES 152–159. Arganthomyza socculata (Zetterstedt) (female, USA: Alaska). 152—spermatheca. 153—postabdomen, dorsal. 154—apex of postabdomen and internal sclerites, lateral. 155—internal sclerites, ventral. 156—end of female genital chamber, lateral. 157—spermatheca. 158—postabdomen, ventral. 159—ventral receptacle, lateral. Scales: Figs 153, 158 = 0.2 mm, Figs 154–156 = 0.1 mm, others = 0.05 mm.

FIGURES 160–165. Arganthomyza socculata (Zetterstedt) (female, Sweden). 160—spermathecae. 161—postabdomen, dorsal. 162—apex of postabdomen and internal sclerites, lateral. 163—internal sclerites, ventral. 164—female genital chamber, lateral. 165—postabdomen, ventral. Scales: Fig. 160 = 0.05 mm, Figs 161, 162, 165 = 0.2 mm, others = 0.1 mm. Adapted from Roháček (2006)

FIGURES 170–172. Wings of Arganthomyza species. 170—A. disjuncta sp. n. (male paratype, Canada: Alberta). 171, 172—A. socculata (Zetterstedt) (males, USA: Alaska). Scale: 0.5 mm.