Hydropeza aptera, Sinclair, 2016

Sinclair, Bradley J., 2016, Revision of the Australian species of Hydropeza Sinclair (Diptera: Empididae: Ragadinae subfam. nov.), Records of the Australian Museum 68 (1), pp. 1-22 : 10-11

Hydropeza aptera sp nov.

Figs 1–3 , 10 , 21

Type material. Holotype ♂, labelled: “TAS: McPartlan Pass,/ 42°51'S 146°11'E / pitfall ARE(Y); 17./ viii.1999; M. Driessen ”; “ HOLOTYPE / Hydropeza / aptera/ Sinclair [red label]” (AMS) . Paratypes: Tasmania: 1♂, same data as holotype, except ARE(Y)4, 14.ix.1999 (AMS) ; 1♀, same data as holotype, except ARE(Y)8, 28.vii.1999 (AMS) ; 2♂♂, McPartlan Pass , buttongrass moorland, 28.vii.1999, pitfall tp, TRW6, 42°51'12"S 146°12'39"E, 320 m, M. Driessen (CNC) ; 1♀, ditto, except TRE(0) 16.v.2000 (CNC) ; 1♂, 4♀♀, Airstrip Rd , sites 1A–6P, 42°51'5"S 146°11'24"E, pitfall tp, 29.v.–5.vi.2001, M. Driessen (AMS) ; 4♂♂, 1♀, ditto, except ARE(Y), 42°50'30"S 146°14'36"E, 320 m, M. Driessen (AMS, CNC) .

Diagnosis. This is the only apterus species of Hydropeza , with the wings reduced to halter-like appendages and legs and scutum with reduced chaetotaxy.

Description. Head and thorax dark brown to black with greyish pruinescence, abdomen brown to black with thin pruinescence; legs dark brown. Wing appendage length 0.3–0.4 mm.

Male. Head. Oval, produced posterodorsally, somewhat flattened dorsally. Ocellar setae short, erect, divergent, inserted between posterior and anterior ocelli; ocellar tubercle with some short setulae; postocellar and postocular setae short and slender; postgenal setae pale, slender, longer than postocellar setae. Face very narrow, closely approximated, lacking setulae. Scape short and slender, subequal in length to pedicel; postpedicel pointed-ovate, longer than scape and pedicel combined, with very short knob-like apical stylus. Proboscis stout and robust, short, extended well beyond mid-length of fore coxa, directed posteriorly; palpus very short, oval about 0.15× length of proboscis, clothed in pale setae; apex of palpus rounded.

Thorax. Greatly shortened and reduced due to apterus condition. Clothed in fine pruinescence; mesonotum with chaetotaxy reduced; scutellum shorted with pair of short, pale apical setae.

Legs. Brown, fore coxa with fine pruinescence, similar to thorax. Inner anterior margin of fore coxa with some 20 dark spine-like setae, mostly concentrated apically and mid-basally; setae not longer than width of coxa. Anterior surface of mid and hind coxae with long brown setae. Legs lacking long, fine setae. Fore femur distinctly broader than mid and hind femora; basal third with 4 long posteroventral setae, longer than femur width; anteroventral face with fine, pale setae. Fore tibia with 4 anteroventral, 2 posteroventral spine-like setae. Fore tarsomere 1 with 4 anteroventral and 4 posteroventral stout setae, anteroventral setae nearly twice longer than posteroventral setae. Mid femur with 4–5 posteroventral setae, nearly as long as width of femur; anteroventral row of short, spine-like setae along entire length. Mid tibia lacking distinct erect setae. Mid tarsomere 1 lacking distinct setae. Hind femur with erect dorsal setae; 1 preapical anterior, 2–3 preapical anteroventral setae. Hind tibia with 1 stout preapical anteroventral seta. Hind tarsomere 1 with biserial row of ventral setae. Tarsomeres of hindleg much longer than tibia; ventral apical margin of tarsomere 4 of fore and midlegs not flattened and expanded; tarsomere 4 of hindleg not laterally compressed ventrally; tarsomere 5 of each leg lacking dorsoapical extension.

Wing. Reduced to halter-like appendage; concolorous with thorax. Halter absent.

Abdomen. Tergites and sternites with short, sparse setae; marginal setae not lengthened. T8 broad, more than half length of T7; setae similar to preceding segments.

Terminalia ( Fig. 10 ). Cercus divided into subrectangular, thinly sclerotized anterior section, bearing short setae; posterior cercus broadly sclerotized medially, with apical row of peg-like setae on either side of distinct median notch. Epandrium small, oval; lamellae separated dorsally beneath cercus by wide membranous gap. Surstylus short, broad and truncate apically, clothed in fine setae only. Hypandrium keel-like, prolonged dorsally into phallic guide; gonocoxal apodeme small, rounded; apex of hypandrium flattened and broad surrounding emerging phallus; postgonites appear fused to apex of hypandrium. Phallus strongly arched at base, tapered to slender recurved tip; ejaculatory apodeme small, apical margin expanded.

Female. Similar to male except as follows: stout setae on fore and midlegs longer and more pronounced. T10 divided medially. Cercus short and rounded apically, slightly longer than width, shorter than length of tergite 10.

Distribution. This species is restricted to Tasmania (Fig. 21), currently known only from the type-locality and apparently active in cold months, from May to September [minimum temperature: July 3.2°C (Dreissen et al., 2013)].

Etymology. The specific name is derived from the Greek apteros (wingless), referring to the virtual absence of wings in this species.

Remarks. All specimens were collected in pitfall traps set out in buttongrass moorland ( Fig. 2 ), which at this location has a shrubby element ( Myrtaceae , Epacridaceae ) as well as monocots ( Cyperaceae and Restionaceae ) dominated by buttongrass ( Driessen et al., 2013). The habitat at approximately 320 m includes many standing pools and riddled with water-filled crayfish burrows (Driessen, pers. comm., 2014). Small streams run through the plains and large lakes occur nearby. In addition, the waters are highly acidic (around pH 4). A montane moorland site (Lake St. Clair, approx. 800 m) was also surveyed by Driessen et al. (2013), but these flightless empidids were not collected.

Wingless or flightlessness among Empidoidea is possibly an adaptation for increased running ability among secretive habitats such as the grasses of the moorland and/or an adaptation to cold conditions which make thermoregulation of thoracic flight muscles difficult ( Hackman, 1964; Bickel, 2006). Included among the pitfall trap samples from McPartlan Pass was another wingless empidoid, Apterodromia tasmanica Sinclair & Cumming ( Hybotidae : Ocydromiinae ). This latter species was originally known from litter samples, collected in January and March (Sinclair & Cumming, 2000). Ground predation, particularly from ants has been cited as a major factor limiting wider development of flightlessness in Diptera ( Bickel, 2006) . However, ant abundance was only lower during the cold months compared to warm months at this lowland moorland ( Driessen et al., 2013, fig. 1).

Figures

Figures 1–2. (1) Hydropeza aptera (drawn by Hannah Finlay). (2) McPartlan Pass, Tasmania, type-locality of H. aptera (photograph: M. Driessen). Scale bar = 0.5 mm.

Figures 3–6. Habitus images of dried mounted male species of Hydropeza, lateral view. (3) H. aptera. (4) H. intricata. (5) H. tasmanica. (6) H. unguicula. Scale bars = 1.0 mm, except Fig. 3 where scale bar = 0.5 mm.

Figures 9–12. Male terminalia of Hydropeza, lateral view. (9) H. angulata (inset showing inner apex of cercus). (10) H. aptera. (11) H. cornuta. (12) H. curvata. Abbreviations: cerc, cercus; ej apod, ejaculatory apodeme; goncx apod, gonocoxal apodeme; pgt, postgonite; ph, phallus; sur, surstylus. Scale bars = 0.1 mm.