Brachycentrus (Sphinctogaster) occidentalis Banks 1911

Brachycentrus (Sphinctogaster) occidentalis Banks

Brachycentrus occidentalis Banks, 1911:355.—Ross, 1938:42.—Fischer, 1970:110.

Brachycentrus fuliginosus Walker.—Denning, 1937:27 [misidentification].

This species is a member of the B. lateralis (Say) subgroup, most closely related to B. fuliginosus Walker. The adult male of B. occidentalis Banks is distinguished by the tenth tergum, which is undivided apicomesally and the apex of the clasper which is drawn out into a very long, mesally directed point.

Unfortunately the larvae of several species of this subgroup are unknown. Among the known larvae, however, only the dark, round- headed form of B. spinae Ross has a similarly uniformly brown head, but it is almost circular in outline, and the tibia of the mid- and hindlegs have 3 or more setae on the inner, basal margin.

ADULT.—Length of forewing, 7–8 mm, 9–10 mm. Color grayish-brown; body nearly fuscous, tibiae and tarsi pale brown; forewing pale brownish-gray, veins distinctly darker. Male abdomen with a posteromesal process from seventh sternum about as broad as long.

Male Genitalia: Ninth segment without a sternal lobe. Cercus elongate, ovoid; cerci divided dorsomesally with inner margins divergent. Tenth tergum elongate, apex truncate in dorsal aspect. Clasper with a long basal area, dorsal section angled posteriad; apex tapering to a point; in posteroventral aspect apex produced into a long, tapering point.

LARVA.—Length to 10 mm. Sclerites light to dark brown, slightly paler over muscle scars on head; legs brown, dorsal margins of femora infuscate. Femora of mid- and hindlegs with three enlarged setae; apicodorsal setae slightly enlarged over, and basodorsal seta indistinguishable from, other dorsal setae; ventral margin with a uniform setal fringe. Tibiae of mid- and hindlegs with a single, ventral, sub- basal seta. Two ventral pairs of submesal setae on first abdominal segment equal in size, but slightly larger than homologous setae on second segment. Lateral fringe from third through seventh segments. Gills single, arising in dorsal, lateral, and ventral rows.

TYPE MATERIAL.—Lectotype, male, MCZ, “Type,” “Bon Accord Brit. Col. 14 May,” “Collection N. Banks,” “Type 11685,” “Lectotype B. occidentalis Bks. Ross 1937 ,” “Brachycentrus occidentalis Type Bks.” Pinned, abdomen cleared, studied.

MATERIAL EXAMINED.—USA, ALASKA, Upper Gulkana River, 1955, G.O. Schumann, 20 (INHS).

ARIZONA, East Fork White River below Greer, 17 May 1964, S.G. Jewett, Jr., 6 pupae. Apache Co., Little Colorado River, Hwy. 373 at Greer, 7 Apr 1968, R.W. Baumann, 2 larvae, 1 prepupa (ROM).

COLORADO, stream at Boulder, J. Henderson, 2 larvae. Del Norte, Rio Grande, 28 Jun 1955, C.P. Alexander, 2, 1 (UMA). Montrose Co., Black Canyon of Gunnison National Monument, 6 Sep 1962, E.B. Reed, 5 larvae. Rio Grande Co., South Fork, 8000 ft., 20 Jun 1972, W.W. Wirth, 1. Routt Co., Yampa River at Steamboat, 19 Jun 1961, A.R. Gaufin, 1.

IDAHO, Twin Falls, 3 May 1937, J.A. Gillett, 23, 7.

MINNESOTA, Bear Creek, Rochester, 25 Apr 1942, P. Harden, 1 (UMSP). Anoka Co., Coon Creek, 25 Apr 1936, C.E. Mickel, 1 prepupa (UMSP). Hennepin Co., Nine Mile Creek, 5 May 1933, C.E. Mickel, 9, 3 (UMSP); same, but 4–8 May 1935, D.G. Denning, 3, 10 reared from pupae, 2 prepupae, exuviae (UMSP); same, but 26 Apr 1936, prepupae, pupae (UMSP); same, but 1 May 1937, D.G. Denning, 7, 5 reared from pupae, pupae (UMSP, USNM).

MONTANA, East Gallatin River near Bozeman, Sep 1971, T. Glorvigan, 20 larvae. Missoula Co., Clearwater River, Hwy. 20 near Clearwater Jct., 17 May 1969, A.R. Gaufin, 4, 4.

NEBRASKA, Royal, 16 Jan 1964, L.H. Dawson, 3 larvae. Cherry Co., Smith Falls, 27 Sep 1967, E.F. Rapp, Jr., 25 larvae.

NEW MEXICO, Río Arriba Co., Río Brazos at Brazos, 8 Jun 1974, Stark and Wolff, 3, 6.

OKLAHOMA, Paine Co., Stillwater, 11 Jun 1959, J.F. Reinert, 5, 1.

OREGON, Corvallis, 7 Apr 1907, Laura Hill, 1 (MCZ).

UTAH, Cache Co., Blacksmith Fork River, Blacksmith Fork Canyon, 4859 ft., 15 Oct 1961, A.V. Nebeker, 20 larvae. Salt Lake Co., Emigration Canyon (creek), 6100 ft., 16 Sep 1966, 8 larvae. Summit Co., Hidden Cove Pond, 14 Oct 1966, R.W. Baumann, 1 larva. Summit Co., Weber River, at Peoa bridge, 10 Nov 1961, 4 larvae; same, but 6191 ft., 14 Oct 1970, G. Yearsley, 25 larvae; same, but near Peoa, under rocks, 16 May 1974, B. Stark, 18, 10; same, but Peoa, 13 May 1976, Baumann et al., 2, 1 (CUC); same, but Rockport, 26 Jan 1976, Surdick and Daleboot, 5 larvae, 1 metamorphotype (decayed) (CUC). Uinta Co., Green River at Dinosaur National Monument, Aug 1967, S.L. Jensen, 6 larvae.

WASHINGTON, Nappel, 21 Apr 1940, J. Standish, 8 (UMSP). Kitatitas Co., Yakima River, ~10 mi. S Ellensburg, 28 May 1957, J.M. Campbell, 12. Spokane Co., Little Spokane River at Milan, 25 Jul 1962, G.F. Edmunds, 25 larvae.

WISCONSIN, Manitowish River, Boulder Junction, 2 Oct 1937, T.H. Frison, 8 larvae (INHS). Adams Co., Big Roche Creek, 8 Nov 1972, 7 larvae (UWM). Adams Co., Big Roche à Cri, 4 May 1970, 5, 1 (UWM). Bayfield Co., North Fork Fish Creek, 6 Oct 1979, 15 larvae (UWM). Bayfield Co., Lower Pine Creek, 12 May 1970, 4 (UWM). Buffalo Co., Church Valley, Hwy. D, 12 May 1970, 1 (UWM). Buffalo Co., Spring Creek, 1 Nov 1972, 30 larvae (UWM). Crawford Co., Baker Creek, Hwy. 61, Griffin Hollow, 29 Apr 1976, 1 (UWM). Dane Co., Mt. Vernon Creek, 13 Dec 1977, P.M. Kotila, 15 larvae (UWM). Dunn Co., Rock Creek, 1 Nov 1972, 6 larvae (UWM). Dunn Co., Eau Salle River. 4 May 1970, 5, 12 (UWM). Florence Co., Lamon- Tangere Creek, 27 May 1970, 1 (UMW). Forest Co., Armstrong Creek, 13 Sep 1972, 4 larvae (UWM). Grant Co., Big Spring Brook, 20 Oct 1980, 6 larvae (UWM). Green Co., Braezels Brook, 5 Nov 1980, 30 larvae (UWM). Iowa Co., Trout Creek, 17 Oct 1979, 50 larvae. Iowa Co., 19 May 1937, F. Snyder, 4, 2 (UMSP). LaCrosse Co., Dutch Creek, 6 Nov 1980, 4 larvae (UWM). Langlade Co., Evergreen River, 17 Oct 1980, 10 larvae (UWM). Marinette Co., Harvey Creek, 26 May 1970, 1, 1 pharate (UWM). Marquette Co., Neenah Creek, 2 Nov 1973, 5 larvae (UWM). Marquette Co., Chaffe Creek, 4 May 1970, 30 (UWM). Marquette Co., Lawrence Creek, 4 May 1970, 4, 4 (UWM). Monroe Co., Squaw Creek, Fort McCoy, 26 Jul 1976, J.C. Morse, 10 larvae (CUC). Polk Co., Cowen Creek, 22 Oct 1980, 10 larvae (UWM). Portage Co., Spring Creek, 1 Dec 1974, Todd and Taylor, 2 larvae (UTK). Richland Co., Branch Mill Creek, N Basswood, 29 Apr 1970, 25, 1 1 in copula (UWM). Richland Co., Melanchton Creek, 27 Apr 1970, 9, 7 (UWM). Richland Co., Ryan Hollow, 29 Apr 1970, 10 (UWM). Richland Co., Grissal Creek, 15 May 1970, 1 (UWM). Richland Co., Core Hollow, 29 Apr 1970, 14 (UWM). Shawano Co., Silver Creek, Red River, 15 May 1979, 6 larvae, 13 pupae (UWM). Vernon Co., Sherry Creek, 15 May 1970, 1 (UWM). Vilas Co., Deerskin River, 15 Oct 1979, 15 larvae (UWM). Waushara Co., Soules Creek, 4 May 1970, 5 (UWM). Waushara Co., Little Pine Creek, Hwy. Y, 4 May 1970, 17 (UWM). Waushara Co., Bird Creek, Hwy. T, 4 May 1970, 4, 5 (UWM). Waupaca Co., Tomonow River, 1 Nov 1974, R. Glesne, 3 larvae (UTK). Waupaca Co., Roddy Creek, 19 Nov 1980, 15 larvae (UWM).

WYOMING, Shoshone River, Shoshone National Forest, 4 Sep 1977, 14 larvae (UMSP). Yellowstone National Park, Yellowstone River, swarm above canyon, 7 Apr 1925, A.C. Burrill, 2, 4; same, but Madison River (T135 R5E S36), 25 Apr 1963, J.R. Heaton, 11, 8; same, but Firehole River, 21 Aug 1962, P.J. Spangler, 10 larvae; same, but Black Sand Basin, 22 Jun 1977, Chapin and Morse, 1 larva (CUC); same, but Lewis River at Lewis Falls, 22 Jun 1977, 17, 1 (CUC). Natrona Co., Sweetwater River, Independence Rock, 21 Jun 1977 Chapin and Morse, 3 larvae (CUC).

CANADA, ALBERTA, Cochrane, 3770 ft., 10 Jun 1952, C.P. Alexander, 1(UMA). Eyremore, 5 May 1926, H.E. Gray, 1 1 (MCZ).

BRITISH COLUMBIA, Bon Accord, 14 May, 1 (lectotype, MCZ); same, but 5 May, Russell, 1 (lectoparatype, MCZ). Oliver, 26 May 1923, C.B. Garrett, 2 1 (MCZ). Nicola, 4 May 1923, E.R. Buckell, 1 (MCZ); same, but 16 May 1922, P.N. Vroom, 1 (MCZ). Nicola Lake, 29 May 1922, E.R. Buckell, 2 1 (MCZ). Trail, 12 May 1927, A.A. Dennys, 1 (MCZ).

MANITOBA, Edwards Creek, Riding Mountain National Park, 11 Jun 1962, reared to 30 Jun 1962, G.B. Wiggins, 1 pupa (ROM). Norgate, stream on Hwy. 19, ∼0.8 mi. W Hwy. 5, 6 Sep 1970, ROM field party, 50 larvae (ROM). McKinnon Creek, Hwy. 361 between Hwy. 5 and Riding Mountain National Park, 6 Sep 1970, ROM field party, 5 larvae (ROM). Cowan Creek, C5–2, 19 May 1980, D.G. Cobb, 5 (FWI).

NORTHWEST TERRITORIES, shore of Mackenzie River near Fort Providence Ferry, 16 Jul 1965, R.A. Evers, 3, 2 (INHS).

SASKATCHEWAN, mossy stream, Hwy. 224, ∼4.5 mi. N Meadow Lake Provincial Park, Goodsoil, 16 Aug 1970, ROM field party, 2 larvae (ROM).

Most likely common.

In North America, from Alaska south to Nevada. B. occidentalis, is mainly confined to western Canada, from Manitoba west to British Columbia and north to the North West Territories (Schmid, 1983).

In adults, the top of the head and thorax are grey-brown and covered with distinct, white hairs. The antennae are dark brown with weak rust-coloured rings. The base of the male clasper is long and extended as a dorsal process, with the horizontal extension curving mesad.

Restricted to running waters.

The larvae are omnivorous, obtaining their food either by filter feeding or scraping.

Brachycentrus occidentalis is a species of humpless casemaker caddisfly in the family Brachycentridae. It is found in North America.