Arganthomyza disjuncta Rohacek & Barber 2013

Arganthomyza disjuncta Roháček & Barber, 2013

(Figs 165, 168–184)

Arganthomyza disjuncta Roháček & Barber, 2013: 34.

Type material. HOLOTYPE: ♀, “CAN: AB: ~1.2kmS Cadom-in, entrance to Whitehorse Wildland PPk., 23.vii.2008, KNBarber, sweeps, Bromus inermis, Hedysarum boreale 53°00.70’N 117°20.05’W ” and “ HOLOTYPUS ♀, Arganthomyza disjuncta sp.n., J. Roháček & K. N. Barber det. 2011” [red label] (DEBU, intact, see Fig. 165). PARATYPES: 120 ♂♂ 94 ♀♀ (AMNH, BIOUG, CASC, CNCI, DEBU, INHS, LACM, LEMQ, RBCM, SEMC, SMOC, UAMF, UBCZ, USNM, ZSMC) (details in ROHÁĆEK & BARBER 2013).

Other material examined (not included in type series). 2 ♀♀ (DEBU, RBCM, damaged) (details in ROHÁĆEK & BARBER 2013).

Additional records. CANADA: ALBERTA: Banff, 28.vi.1966, 1 ♀; Edmonton, 14.vi.1966, 1 ♂, both K.A. Spencer leg. (both BMNH, both genit. prep.); Sheep Creek Prov. Pk., 54°03.6'N 119°00.7'W, sweep at campground, 22.vii.2003, 1 ♂ 1 ♀, S. Boucher leg. (LEMQ 0040460, -61). UNITED STATES OF AMERICA: UTAH: Cache Co., Tony Grove Canyon, Malaise trap, 19–27.vii.1983, 1 ♀, W. J. Hanson leg. (LACM, ENT 329102).

Diagnosis. Male 1.94–2.38 mm, female 2.10–3.02 mm. Virtually identical externally to A. socculata. Reference to the genitalia is necessary to conndently distinguish typical members of this species (see discussion regarding separation of males of A. disjuncta and A. socculata below). Male genitalia (see Figs 168–175 for details). Epandrium (Figs 168, 170) blackish brown, distinctly higher than long. Gonostylus (Figs 168, 170, 175) ochreous to yellow, nat, slightly bent medially, more elongate than in A. socculata, tapered distally, with rounded apex, largely micropubescent on outer side and largely setose on inner side. Its anterior margin with more or less distinct concavity in the middle and posterior margin less concave than in A. socculata (in largest extension view). Hypandrium anterior to pregonite hardly or little excavated (Fig. 171). Pregonite with posterior lobe more robust and somewhat projecting (Fig. 171). Aedeagal part of folding apparatus with dark granulose tubercles on proximal part (Fig. 174) reduced both in number and size in contrast to those of A. socculata.

Female postabdomen and genitalia (see Figs 176–183 for details). Sclerites of 7th abdominal segment markedly different from those of A. socculata: T7 and S7 clearly separate though closely appressed. T7 larger and longer than in A. socculata, extended far onto ventral side and with spiracles embedded near its anteroventral corners (Fig. 178). S7 large, wide and pale anteriorly, tapered, darker and with rounded corners posteriorly, entirely and distinctly micropubescent, with dark-pigmented transverse stripe near anterior margin and with 6 long setae at posterior to posterolateral margin (Fig. 178). Ventral receptacle (Fig. 179) hyaline, slender, relatively long, proximally wider tubular, distally tapered to form sinuate slender apical part with blunt tip. Spermathecae (1+1) resembling those of A. socculata, short-pyriform, with dark transversely striated surface, but slender bases provided with rosette of only 3 bell-shaped appendages (see Fig. 176), some of which have doubled apex.

Discussion. Arganthomyza disjuncta is closely related and extremely similar to the Holarctic A. socculata. The species is peculiar for the large and separate female S7 (see Fig. 178), a character unknown in all other congeners where S7 is fused with T7 to form a compact annular tergosternum T7+S7. Although the separate S7 surely is a plesiomorphic condition, it is considered by ROHÁĆEK & BARBER (2013: Fig. 173) to have evolved secondarily in this species, as a reversal of the S7 integrated into the tergosternal sclerite T7+S7 which otherwise is a distinct synapomorphy of the genus Arganthomyza.

While the female of A. disjuncta can be easily identined by the separate S7, only 3 bell-shaped appendages on the spermatheca and the very elongate annular sclerite in the genital chamber, differentiating males of A. disjuncta from those of A. socculata is sometimes difncult. There are slight differences in the form of the gonostylus, hypandrium and pregonite (see the key and description above), but usage of these characters requires careful comparison and observation at various angles. The separation of males of these two species is further complicated by great variability of the gonostylus in both A. socculata and A. disjuncta, and the occurrence of unidentinable specimens (those not possessing typical shapes of gonostylus, hypandrium and pregonite in combination) in localities where both species occur together (connrmed in Alaska).

Biology. Very little is known of the biology of A. disjuncta except for preferred habitats that, at least in western North America, appear to be open and dominated by graminoids (Figs 166, 167), most often by grasses including the introduced weedy Bromus inermis Leyss (ROHÁĆEK & BARBER 2013). Riparian habitats have also been mentioned while “mouse runs” directs attention to the thatch layer (although most specimens have been swept from vegetation). This species co-occurs with A. socculata in some sites in Alaska. A single specimen of A. bivittata and two specimens of A. duplex (Alberta: Cadomin) were taken with a series of A. disjuncta while a single specimen of A. disjuncta was taken with a series of A. duplex (Alberta: Dunvegan). Adults have been collected from 2 June (British Columbia: south of Atlin) to 1–7 September (Utah: Tony Grove Jct.).

Distribution. Widely distributed in Canada (Alberta, British Columbia, Labrador, Manitoba, Northwest Territories, Quebec, Saskatchewan, Yukon) especially in montane areas of Alberta and British Columbia. Transcontinental, though collected infrequently and mostly in northerly sites east of Saskatchewan – notably with old records from south-central Saskatchewan and no records from Ontario. Also known in the United States of America (Alaska, Colorado, Montana, Utah) with at least some Utah records from high elevations (ROHÁĆEK & BARBER 2013, see Table 2).