Acanthocnema torrenticola, Sinclair, 2025

Sinclair, Bradley J., 2025, Revision of the Nearctic species of Acanthocnema Becker, 1894 (Diptera: Scathophagidae), European Journal of Taxonomy 1026, pp. 304-337 : 327-333

Acanthocnema torrenticola sp. nov.

urn:lsid:zoobank.org:act:

Figs 1–3, 49–60

Diagnosis

This species is distinguished by the blackish ground colour, densely blue-grey pruinescent laterally, brown dorsally, palpus pale to dark brown in both sexes, orbital setae lateroclinate, fore tibia without row of short, black anteroventral setae and male sternite 5 without apical lobes.

Etymology

The specific epithet is derived from the Latin ‘ torrens ’ (‘rushing’, ‘rapid’), in reference to the fastflowing streams, creeks and rivers where it has been collected.

Material examined

Holotype

USA – Idaho • ♂; “ USA: ID: Idaho Co. / Clearwater NF; Hwy 12 / Apgar Ck, 13.vi.2011 / N 46°12′53.0″W 115°32′13.6″ / B.J. Sinclair // CNC / 905983 // HOLOTYPE / Acanthocnema / torrenticola / Sinclair [red label]”; CNC, CNC905983 .

Paratypes

CANADA – Alberta • 1 ♂; Peter Lougheed PP, Grizzly Ck; 50°45.890′ N, 115°8.379′ W; 1695 m a.s.l.; 9 Jul. 2012; B.J. Sinclair leg.; forest and creek; CNC . – British Columbia • 1 ♂, 1 ♀; Cathedral PP, Ashnola River ; 49°08.13′ N, 120°02.12′ W; 750 m a.s.l.; 19 Jul. 2015; B.J. Sinclair leg.; CNC • 1 ♂, 1 ♀; Cowichan Lake, Honeymoon Bay ; [ 48.818° N, 124.172° W]; 6 Jun. 1955; G.E. Shewell leg.; CNC • 1 ♀; Marysville, Marysville Falls, Mark Ck ; 49°38.13′ N, 115°57.64′ W; 940 m a.s.l.; 16 Jul. 2015; B.J. Sinclair leg.; CNC • 1 ♂; Mt Revelstoke NP, Giant Cedar Trail ; [ 51.106° N, 117.906° W]; 700 m a.s.l.; 2 Jul. 1989; B.J. Sinclair leg.; cascading stream; CNC • 1 ♀; Terrace, Eliza Ck ; [ 54.420° N, 128.532° W]; 22 Jun. 1960; G.E. Shewell leg.; resting on black fly cage; CNC • 1 ♂; same data as for preceding; 26 Jun. 1960; CNC • 1 ♀; same data as for preceding; 29 Jun. 1960; from black fly cage in stream; CNC • 1 ♂; same data as for preceding; 13 Jul. 1960; cage trap in stream; CNC • 1 ♂; 20 mi. N of Terrace, Kitsumkalum Lake ; [ 54.725° N, 128.773° W]; 31 May 1960; G.E. Shewell leg.; CNC • 1 ♂; 49 mi. W of Terrace, Slickenslide Ck ; [ 54.211° N, 129.603° W]; 9 Jul. 1960; J.G. Chillcott leg.; CNC • 1 ♀; Perry Creek Falls Trail; 49°32.977′ N, 115°59.837′ W; 1095 m a.s.l.; 11 Jun. 2012; B.J. Sinclair leg.; cascading stream; CNC • 1 ♂, 2 ♀♀; W Creston, Hwy 3, Topaz Ck ; 49°08.76′ N, 116°45.65′ W; 825 m a.s.l.; 18 Jul. 2015; B.J. Sinclair leg.; CNC . – Ontario • 1 ♂; Collingwood Twsp, Black Ash Ck ; [ 44.494° N, 80.242° W]; 15 May 1948; F.P. Ide leg.; CNC • 1 ♂; Grey Co., Eugenia ; [ 44.313° N, 80.526° W]; 27 Apr. 2008; S.A. Marshall leg.; DEBU • 1 ♂; Forks of the Credit PP, Credit R; 43°48′49.60″ N, 80°0′56.95″ W; 19 Jun. 2023; B.J. Sinclair leg.; CNC • 1 ♀; Halton Co., Lowville Pk, Bronte Ck ; 12 May 1990; B.J. Sinclair leg.; CNC • 1 ♂, 4 ♀♀; same data as for preceding; 43°26′3.35″ N, 79°54′12.83″ W; 23 Apr. 2023; CNC • 1 ♂, 2 ♀♀; Wellington Co., Fergus ; [ 43.691° N, 80.386° W]; 3 Apr. 2000; S.A. Marshall leg.; on rocks in river; DEBU • 1 ♀; same data as for preceding; 10.Sep. 1995; DEBU • 1 ♂, 1 ♀ (in copula), 1 ♂; same data as for preceding; 20 Sep. 1995; DEBU • 1 ♂, 1 ♀ (in copula), 2 ♂♂, 2 ♀♀; same data as for preceding; Grand River ; 2 Oct. 1995; DEBU • 1 ♀; Wellington Co., Guelph, Speed R. at Victoria Rd ; [ 43.588° N, 80.273° W]; 1 May 1998; S.A. Marshall leg.; on rocks in riffle; DEBU . – Quebec • 1 ♀; Old Chelsea ; [ 45.499° N, 75.814° W]; 20 Sep. 1955, J.R. Vockeroth leg.; CNC • 1 ♂, 3 ♀♀; same data as for preceding; 26 Sep. 1955; CNC • 1 ♀; same data as for preceding; 27 Sep. 1955; KUMF . – Yukon • 1 ♀; Whitehorse, Lewes River ; [ 60.391° N, 134.833° W]; 24 Jun. 1949; L.R. Pickering leg.; CNC • 1 ♂; same data as for preceding; 30 Jul. 1949; CNC • 1 ♂, 1 ♀; same data as for preceding; 2 Jul. 1949; cage N.2; CNC • 3 ♂♂, 2 ♀♀; same data as for preceding; 4 Jul. 1949; CNC • 3 ♂♂; same data as for preceding; 6 Jul. 1949; CNC • 1 ♂; same data as for preceding; 7 Jul. 1949; S.1; CNC • 1 ♀; same data as for preceding; 8 Jul. 1949; cage S.1; CNC • 7 ♂♂, 1 ♀; same data as for preceding; 9 Jul. 1949; CNC • 1 ♀; same data as for preceding; KUMF • 1 ♂; same data as for preceding; 13 Jul. 1949; cage S.2; CNC • 1 ♀; same data as for preceding; 19 Jul. 1949; S.2; CNC • 1 ♀; same data as for preceding; 22 Jul. 1949; CNC • 2 ♂♂; same data as for preceding; 27 Jul. 1949; cage N.2; CNC • 1 ♀; same data as for preceding; 29 Jul. 1949; cage N.2; CNC • 1 ♂, 1 ♀; same data as for preceding; 1–17 Aug. 1949; CNC • 1 ♂; same data as for preceding; 9 Aug. 1949; KUMF • 1 ♂; same data as for preceding; mile 906; 9 Sep. 1949; cage S.5; CNC • 1 ♂; same data as for preceding; 31 Aug. 1949; CNC .

USA – Alaska • 1 ♂; mile 14, Richardson Hwy; [ 61.067° N, 145.905° W]; Horsetail Falls ; 18 Jul. 1993; T. Saigusa leg.; KUMF • 1 ♂, 1 ♀; mile 206, Richardson Hwy ; [ 63°11′15″ N, 145°33′29″ W]; 20 Jul. 1987; M. Wood leg.; beaver pond; CNC. – California • 1 ♀; El Dorado Co., South Fk American River, Eagle Rock river access; 38°46′34.6″ N, 120°16′00.7″ W; 18 Jul. 2012; J.M. Cumming leg.; CNC • 1 ♀; Marin Co., Alpine Lake, Lily Pond ; [ 37.953° N, 122.634° W]; 1500 ft a.s.l.; 1–12 Mar. 1970; D.D. Munroe leg.; MT; CNC • 1 ♂, 1 puparium; Marin Co., Mt Tamalpais SP, Redwood Ck , 12 mi. N of San Francisco; 37°52′ N, 122°34′ W; 20 m a.s.l.; 23 Nov. 2005; A.H. Purcell leg.; em. 23–24 Jan. 2006; CNC • 1 ♂; same data as for preceding; em. 21 Mar. 2006; CNC • 1 ♀, 1 puparium (in alc.); same data as for preceding; em. 6 Feb. 2006; EMEC • 1 ♂, 1 puparium (in alc.); same data as for preceding; em. 24 Feb. 2006; EMEC • 1 ♀, 1 puparium (in alc.); same data as for preceding; em. 24 Feb. 2006; EMEC • 1 ♂, 1 puparium (in alc.); same data as for preceding; em. 28 Mar. 2006; EMEC • 1 ♀, 1 puparium (in alc.); same data as for preceding; em. 7 Apr. 2006; EMEC • 1 ♀; Nevada Co., Prosser Ck at Hwy 89; 39°23′50.2″ N, 120°11′13.9″ W; 14 Jul. 2012; S.E. Brooks leg.; CNC. – Colorado • 1 ♀; Archuleta Co., Devil’s Ck ; 37°12′58″ N, 107°17′41″ W; 6660 ft a.s.l.; 17 Jun. 2017; J.M. Cumming leg.; CNC • 1 ♂; Boulder Co., So. St. Vrain Ck ; [ 40°16′ N, 104°52′ W]; 8 Sep. 1950; W.W. Wirth leg.; USNM. – Idaho • 2 ♀♀; Gooding Co., Niagara Springs ; [ 42.662° N, 114.671° W]; 29 Apr. 1972; R.L. Newell leg.; CNC • 1 ♂; same data as for preceding; 30 Jan. 1973; R.L. Newell and D.S. Potter leg.; USNM • 1 ♀; Idaho Co., Clearwater NF, Hwy 12, 3 Devils Picnic Area , 2–3 km W of Lowell; 46°08.155′ N, 115°38.681′ W; 450 m a.s.l.; 13 Jun. 2014; B.J. Sinclair leg.; small stream; CNC • 1 ♂, 1 ♀; same data as for holotype; CNC. – Maine • 1 ♂, 2 ♀♀; Mt Katahdin, Katahdin Falls ; [ 45.909° N, 68.950° W]; 1600 ft a.s.l.; 2 Jul. 1968; P. Ward leg.; CNC. – New Mexico • 1 ♂; James Springs ; [ 34.549° N, 104.364° W]; 4 Jul. 1953; W.W. Wirth leg.; USNM. – Oregon • 1 ♂, 1 ♀; Benton Co., Alsea Falls ; 44°19′31.70″ N, 123°29′25.11″ W; 250 m a.s.l.; 5 Jul. 2014; J.M. Cumming leg.; CNC • 1 ♂; Hood River Co., 2 mi. E of Parkdale, East Fk Hood River ; [ 45.530° N, 121.578° W]; 11 Jul. 1989; B.J. Sinclair leg.; CNC • 1 ♀; Marion Co., Willamette NF, French Ck Rd , French Ck ; 44°46.423′ N, 122°12.683′ W; 840 m a.s.l.; 10 Jul. 2013; B.J. Sinclair leg.; CNC • 1 ♀; E Wallowa ; [ 45.570° N, 117.529° W]; 15 Jul. 1949; G.H. and J.L. Sperry leg.; USNM. – Pennsylvania • 1 ♂; Sullivan Co., Wyoming SF, 8 km NW of Laporte ; [ 41°0′2″ N, 76°27′14″ W]; 6 May 1987; J.M. Cumming leg.; CNC. – Utah • 1 ♂; Salt Lake Co., Red Butte Canyon ; [ 40°48′51″ N, 111°44′51″ W]; 1 Jul. 1953; B.V. Peterson leg.; CNC • 1 ♂; “Wheeler Sawmill & Cabin”; 39.958° N, 111.267° W; 9 Jun. 2011; B.J. Sinclair leg.; spring stream; CNC. – Washington • 1 ♂; Husum ; [ 45.800° N, 121.485° W]; 26 Jul. 1921; A.L. Melander leg.; USNM • 2 ♀♀; Whatcom Co., Mt Baker, Dead Horse Ck ; [ 48.898° N, 121.835° W]; 8 Aug. 1982; M. Wood leg.; CNC • 2 ♂♂, 2 ♀♀; Mt Rainier, Ohanapecosh ; [ 46.732° N, 121.569° W]; 11 Aug. 1940; A.L. Melander leg.; USNM. – Wyoming • 1 ♀; Yellowstone Pk, Cascades , Y.R. [Yellowstone River?]; [ 44.71° N, 110.49° W]; 22 Jul. 1923; A.L. Melander leg.; USNM .

Description

Body blackish in ground colour ( Fig. 49), densely blue-grey pruinescent laterally, brown dorsally. Body length: 4–5 mm; wing length: 4–5.6 mm.

Male

HEAD ( Figs 49–50). Frontal vitta completely black, matt; fronto-orbital plate black, grey pruinescent, with numerous black setulae. Chaetotaxy: 3–4 lateroclinate orbitals; 1–2 inclinate frontals; 1 ocellar, 1 inner vertical, 1 outer vertical; postocellar setae very weak, convergent; row of dark postocular setae; 1 vibrissa, 1 strong subvibrissa. Gena silvery pruinescent, broad, depth below eye subequal to length of postpedicel; postgenal setae white, soft, shorter than width of postgena. Face, parafacial and occiput silvery pruinescent. Palpus pale yellowish brown with long white setae. Proboscis with broad, shiny prementum, without setae. Antenna black; postpedicel rounded apically, 2 × as long as broad. Arista pubescent on basal quarter and bare apically.

THORAX ( Fig. 49). Dark brown with greyish postpropronotal lobe, notopleuron, prescutellar depression and scutellum; whitish vitta along acrostichal series anteriorly; pleura and mediotergite with greyish pruinescence. Acrostichals biserial, short, slender; 2+(3–4) dorsocentrals; 1+2 intra-alars; 1+1 supra-alars; 1 postpronotal; 2 notopleurals, 2 postalars; scutellum with pair of strong apical setae and pair of strong basal setae; lateral margins and dorsal surface of scutellum apically densely clothed in black setae and setulae. Dark proepisternal seta present. Proepimeral seta present. Anepisternum with dark setae on posterior half and 1 long seta and several long thinner setae near posterior margin. Katepisternum with 1 strong seta in posterodorsal corner and numerous yellow setulae.

LEGS ( Fig. 51). Black, densely greyish pruinescence. Fore femur with 4–6 posteroventral setae extending beyond dense setulae. Fore tibia with ventral apical spur, 1 anterodorsal at mid-length and 1 posteroventral seta at apical fourth; without row of short spinules ventrally. Mid femur with row of anterodorsal setae, with 1 preapical posterodorsal and 1–2 posterior preapical setae. Mid tibia with or without 1 anterodorsal seta and 1 posterodorsal seta beyond mid-length; 1 anteroventral seta and 1 posteroventral apical seta. Hind femur with row of anterodorsal setae. Hind tibia usually with 1 anterodorsal seta and 1 posterodorsal seta beyond mid-length; 1 dorsal preapical seta.

WING ( Fig. 49). Infuscate, without band; veins black; crossvein dm-m at right angles, not aligned with M 4; M 4 strong beyond cell dm, one-quarter length of crossvein dm-m; CuA+CuP strong on basal two-thirds, weakened to wing margin. Calypteres and halter pale brown.

ABDOMEN. Similar to thorax, brownish dorsally, blue-greyish pruinescent laterally; without long ventrolateral setae. Sternite 4 narrow, about 2 × as wide as long, slightly tapered ( Fig. 52). Sternite 5 broad, without lobes; posterior margin with slight median cleft ( Fig. 52). Terminalia ( Figs 53– 54): Epandrium rounded, broad. Cercus short, apical margin rounded in lateral view; cerci closely approximated medially. Surstylus digitiform, sinuous in posterior view; apex rounded with series of ridges on margin. Phallapodeme elongate, rod-shaped. Pregonite short, straight lobe, with several short apical setae. Postgonite gently arched with rounded apex. Ejaculatory apodeme flattened and expanded with expanded ejaculatory duct. Distiphallus narrow, tube-shaped.

Female

Similar to male except, palpus brown; tergite 7 subtriangular, fused anterolaterally with sternite 7, dorsally tapered and medially divided; sternite 7 subtriangular, fused anterodorsally with tergite 7; tergite 8 U-shaped, enclosing proctiger, narrowly divided medially, obliquely angled; sternite 8 divided into pair of tapered digitiform lobes, directed dorsally; epiproct and hypoproct small, triangular; cercus oval, thinly sclerotized ( Fig. 55). Three spermathecae tubular, narrow posteriorly, expanded anteriorly.

Larval cephaloskeleton (removed from puparium)

Robust, brown ( Fig. 56); intermediate sclerite enlarged, well sclerotized; cibarial pump without ventral ridges; base of mouthhook broad with hollow central region; apex of mouthhook bifid with row of distinct teeth between projections, best seen in ventral view ( Fig. 57).

Puparium

Dark brown, clothed in microtrichia; terminal abdominal segment with pair of rounded dorsal tubercles, single rounded lateral tubercle and paired of rounded ventral tubercles ( Fig. 58). Posterior spiracular plate with ecdysial scars positioned at 3 and 9 o’clock positions; spiracular opening straight, radiating from ecdysial scar at less than right angles ( Fig. 59).

Distribution

This is the most widespread species, extending across the continent from New Brunswick to the Alaska and south to New Mexico ( Fig. 60).

Remarks

The life history of this species (as Acanthocnema sp. ) was studied by Purcell et al. (2008). Females oviposit on the egg masses of aquatic insects found on the downstream faces of rocks and in their study mostly on egg masses of the caddisfly Neophylax rickeri Milne, 1935 . Purcell et al. (2008) found that in California, A. torrenticola had a bivoltine life cycle. The first generation fed exclusively on N. rickeri egg masses in the winter and the second generation fed on the egg masses of a variety of species, including other Trichoptera ( Brachycentridae ) and Diptera ( Ceratopogonidae , Chironomidae ) in the spring.

In Ontario, adults have been collected in early spring and mating pairs were collected in September and October based on the material examined above.