Xylota norma Grove & Skevington, sp. nov.

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Holotype, ♂, AUSTRALIA: Tasmania: Tarkine, Balfour Track Forest Reserve, vicinity of Stephen's Rivulet, -41.1523, 144.9465, riverine rainforest flats, 12.ii.2022, S.J. Grove, Malaise trap, F128353 (TMAG). Paratypes (all from the same Malaise trap and locality as holotype, and all collected by S.J. Grove): 1♀, 29.xii.2021, TMAG: F128620; 3♀♀, 12.ii.2022, TMAG: F128354, CNC: 1866758, ANIC: 29-065926; 1♀, 21.iii.2022, TMAG: F128176.

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Figures 3–4. Xylota norma sp. nov., holotype, general habitus photos. 3: Left lateral view, scale bar = 1 mm, inset shows original collection label; 4: Dorsal view, scale bar = 1 mm.

Figures 5–7. Xylota norma sp. nov., holotype, detailed habitus photos. 5: Right wing, showing vestiture and darkening, scale bar = 1 mm; 6: Front view of head, scale bar = 0.5 mm; 7: Left lateral view of tip of abdomen, showing pile, scale bar = 0.5 mm.

Figures 8–11. Xylota norma sp. nov., holotype, genitalia. 8: Right lateral view of cercus and surstylus (with left cercus and surstylus in background), scale bar = 0.25 mm; 9: Dorsal view of cerci and surstyli, scale bar = 0.25 mm; 10: Dorsal view of hypandrium and distiphallus, scale bar = 0.25 mm; 11: Right lateral view of hypandrium and distiphallus, with basal, dorsally projecting cone-shaped sclerotised structure arrowed, scale bar = 0.25 mm.

Diagnosis. Basal two-fifths of metafemur yellow. Metatarsus entirely dark, at least dorsally. Pro- and mesotarsi predominantly dark, except basally. Face densely yellow-pollinose. Haltere bright yellow. Calypter pale yellow. Wings slightly darkened apically and anteriorly. The only other known Australian species, Xylota flavitarsis Macquart, 1846, is marginally larger on average (body length: 9.5 to 14 mm; wing length: 8 to 11 mm) and has all femora entirely dark or at most slightly paler towards apices; all tarsal segments 1-3 entirely yellow; face dark but silvery pollinose; haltere pale brown or greyish; calypter off-white; and wing hyaline throughout.

Description.

Size: Body length: 9.0 to 10.5 mm; wing length: 7.9 to 9.5 mm.

MALE. Habitus as in Figures 3-7. Head: Black; frontal triangle sparsely yellow pollinose; face densely yellow pollinose; gena shiny throughout, bare anteriorly, sparsely white pilose posteriorly; frontal lunule bare shiny black, vertical triangle shiny black but pale pollinose anterior to ocellar triangle, sparsely dark pilose; occiput matte black, predominantly pale pilose; antenna dark brown, postpedicel substantially yellow pollinose especially on inner face, arista bare, black, elongate, ~2.7 times as long as postpedicel.

Thorax: Black; postpronotum and mesonotum shiny, reflecting bronze, with dense short erect yellow pilosity and with longer yellow pili anterolaterally; post-alar callus shiny, with sparse pale pili; scutellum shiny, with sparse pale pili; subscutellar fringe long and pale, denser medially than laterally; pleuron semi-shining, sparsely white pollinose and sparsely white pilose, without distinct anepisternal seta; metathoracic spiracular fringe brown. Wing (Figure 5): hyaline basally and posteriorly, somewhat darkened brown apically and anteriorly; stigma very dark; vena spuria darkened and microtrichose throughout, broadening into a dark smudge around mid-point; microtrichose except bare cell h, basal third cell c, basal half cell br, basal half cell bm, anterobasal edge of cell cua, and narrowly anterior to vein A1; calypter yellow; haltere yellow. Legs: Coxae black, pale pollinose, procoxa finely yellow pilose, meso- and metacoxa white pilose; metatrochanter with distinct posterior tubercle; profemur white and yellow pilose, black except apex narrowly yellow-brown, mesofemur white pilose, black except base and apex narrowly yellow-brown, metafemur white pilose in basal two-thirds, appressed black pilose in apical third, black except bright yellow in basal two-fifths, short stout black ventral setae on apical two-thirds; protibia black except basal quarter dull yellow, densely appressed short yellow pilose anteriorly, less densely appressed short white pilose elsewhere, mesotibia black except basal fifth dull yellow, sparsely appressed short white pilose throughout, metatibia black throughout, appressed short dark pilose throughout; protarsal segment 1 yellow except brown apically, 2 dark brown, 3-5 black, mesotarsal segments 1-2 yellow except dark brown apically, 3 narrowly yellow basally, remainder dark brown, 4-5 black, metatarsus black dorsally, appressed dense short yellow pilose ventrally.

Abdomen: Generally matte blue-black, tergites 2-3 finely transversely rugose towards midline, faint rectangular semi-shiny dorsolateral blue-black maculae clothed laterally with long white pilosity occupying half length of tergite and beginning at basal one-sixth, each one-third the width of the tergite, only discernible with oblique lighting, tergite 4 white pilose laterally, tending to black pilose apically; sternite 1 shiny black medially, pale pollinose laterally, sternites 2-4 shiny black, sternites 1-3 sparse white pilose, sternite 4 appressed short black pilose, with longer black pili on apical margin.

Genitalia: Externally, black, shiny and black pilose (Figure 7); epandrium compact, about as long as wide; cercus (Figure 8) rhomboidal, narrower basally than apically, with apex broadly rounded, apico-dorsal face straight in lateral view, dorsal angle obtuse; surstyli (Figures 8-9) with medial lobe left-right asymmetrical, each medial lobe in both dorsal and lateral views relatively broad, not elongate, dorsal surface angled obtusely downwards slightly beyond midpoint, tapering towards blunt apex, ventral surface straight; lateral lobe of surstyli left-right symmetrical, each lateral lobe in lateral view (FIgure 8) truncate, subquadrate, projected ventrally rather than forwards-facing, as wide basally as apically, with apical face convex; distiphallus spathulate in dorsal view, slightly indented medially at tip as well as mediolaterally; gonostylus (Figures 10-11) indistinct, rounded apically, lacking heavily sclerotised spines or flanges but bearing a single dorsally projecting cone-shaped sclerotised structure basally, most visible in lateral view (Figure 11, arrowed).

FEMALE. Similar to male except for normal sexual dimorphism (such as eyes dichoptic), and frons shiny.

Figures 3–4. Xylota norma sp. nov., holotype, general habitus photos. 3: Left lateral view, scale bar = 1 mm, inset shows original collection label; 4: Dorsal view, scale bar = 1 mm.

Distribution & habitat. Australia: Tasmania. Only known from the type series, collected by SJG at a single locality in the Tarkine rainforests in the northwest of the state. Xylota flavitarsis also occurs widely in this region, although it is not yet reported from this precise locality. The type locality comprises cool temperate rainforest dominated by Nothofagus cunninghamii (Hook.) Oerst. adjacent to mixed forest with a rainforest understorey and a tall eucalypt (Eucalyptus obliqua L'Hér.) overstorey. Larvae likely to be associated with rotting wood or other organic-rich substrate. Given that the only Malaise trap that caught adults at this locality was within 20 m of a woody debris-choked creek (a tributary of Stephen's Rivulet; the other three traps in operation at the time were 50-200 m distant from the creek), it is possible that there is a larval association with waterlogged wood, as in some Chalcosyrphus species.

Flight season. Based on collected specimens, the flight seasons appears to be, conservatively, late December to mid-February; possibly mid-November to late March. Adults were extracted from trap samples collected between the end of December and late March; the earliest of these specimens was extracted from a sample that had been accumulating insects since mid-November, while the latest was extracted from one that had been accumulating since mid-February.

Etymology. This species is dedicated to the late Norma Herd, whose estate allowed her daughter Chris, SJG’s wife, to purchase a second-hand campervan, also called Norma, which in turn made his Tarkine insect-collecting trips both feasible and comfortable. The epithet also happens to be an anagram of morna, which applies to a species of Xylota described from northern Borneo (Curran, 1931). It is to be treated as a noun in apposition.

Common name. We suggest referring to this species as the Tarkine leaf-walker, and to X. flavitarsis as the Australian leaf-walker.