Setacera pacifica (Cresson 1925)

Setacera pacifica (Cresson)

Ephydra pacifica Cresson, 1925:167.

Setacera pacifica.—Cresson, 1930:116.—Sturtevant and Wheeler, 1954:202, 203 [key and locality data].—Wirth and Stone, 1956:472 [key].—Wirth, 1965:755 [nearctic catalog].—Cole, 1969:402 [locality data].

DESCRIPTION.—Moderately large to large shore flies, length 4.09 to 5.12 mm; dorsum generally green to olivaceous brown, becoming grayish green to green ventrally, duller.

Head (Figures 109, 116–118): Head width-to-height ratio averaging 1 : 0.66; frons width-to-length ratio averaging 1 : 0.49; mesofrons, fronto-orbits, and at least posterior portion of dorsum of interfoveal carina deeply bluish to greenish blue, anterior portion of interfoveal carina sometimes more greenish; arista with longest dorsally branching rays nearly twice aristal width at base; dorsal surface of face moderately explanate, antennal foveae only slightly lower and inclined than dorsum of interfoveal carina, nearly horizontal; dorsal surface of face shorter than anterior surface, facial angle about 95°; angle formed by anterior surface and oral margin; eye height-to-width ratio averaging, 1 : 0.98; eye-to-cheek ratio averaging 1 : 0.44.

Thorax (Figures 110, 119–124): Supraspiracular convexity with papilla-like, lateral projection toward anterodorsal portion (Figures 123, 124); fore- and midcoxae of male (Figure 121) with dense patches of long setae, especially ventrally and posteroventrally; front basitarsus of male with long, fine, pale setae ventrally; mid- and hind tibiae of male with slightly more dense patch of setae apicoventrally; costal vein ratio averaging 1 : 0.28; M1+2 vein ratio averaging 1 : 0.83.

Abdomen: Male 5th tergal ratio averaging 1 : 0.81; 5th tergum of male lacking an anteroventral projection. Male terminalia (Figures 111–113): epandrium with shallow, median furrow; surstyli, in posterior view, with base rounded laterally, projecting processes narrow, tapered to acutely pointed apices, each process curved anteriorly in lateral view, median projection triangular, wider at base than more lateral processes, median projection, in lateral view, situated anterior of processes and slightly curved posteriorly; gonite with 3 posteriorly projecting prongs, dorsomedial pair more heavily sclerotized, apex slightly curved dorsally, median and ventral pairs along same lateral plane, median prong wider and shorter, more or less straight, ventral prong narrow and generally curved ventrally; aedeagus folded back on itself, rounded apically; hypandrium more or less evenly sclerotized, prongs and extreme lateral margins more heavily sclerotized, median plate area very shallow, with 2 prongs, posteromedian pair oriented medially, subapically more abruptly tapered, curved, clawlike, anterolateral prong evenly tapered, mostly straight. Female terminalia (Figures 114, 115): 7th tergum incomplete, formed by 2 lateral tergites; 8th tergites higher than wide in lateral view, dorsum pointed, venter rounded, anterior margin more or less straight, posterior margin straight to very shallowly concave; 8th sternites over 6 times longer than wide; cercus as wide or wider than high, roughly subquadrate, posterior margin broadly rounded to subtruncate; female ventral receptacle (Figure 115) with operculum mostly rounded dorsally and laterally, otherwise as in species group description.

TYPE MATERIAL.—The male holotype is labeled: “Vancouver 5 IV[Apr]′[19]02 B[ritish] C[olombia] R J. Crew//TYPE No. 6344 Ephydra PACIFICA E T Cresson, Jr. [red].” The holotype is in the Academy of Natural Sciences of Philadelphia, ANSP 6344. The specimen is pinned directly and is in good condition, although all tarsomeres except for the basitarsus of the right midleg are missing.

OTHER SPECIMENS EXAMINED.—CANADA. British Columbia: Oliver, 12 Aug 1953, 1000 ft, D. F. Hardwick (1, 1; CNC); Oliver, McIntyre Creek, 6 Jun 1959, R. E. Leech (1; CNC); Oliver, White Lake, 28 May 1959, L. A. Kelton (2; CNC); Vancouver Island, Cowichan Island, 12 Jul 1924, A. L. Melander (1, 1; USNM); Vernon, 31 Aug 1937, H. Leech (2; CNC Manitoba: Aweme, 4 Oct 1923, N. Criddle (1; CNC); Whitewater Lake, 4 mi N Whitewater, 30 Jul 1958, R. L. Hurley (1; CNC UNITED STATES. California: Lassen Co., Susanville, 41 mi NW, 17 Jun 1974 (1; USNM San Bernardino Co., Barton Flat, S Fork Camp, 31 Aug–3 Sep 1944, A. L. Melander (2, 2; USNM), Big Bear Lake, 24 May–26 Jul, 1932–1966, R. H. Beamer, A. L. Melander, R. E. Orth (3, 3; KU, UCR, USNM), Upper Santa Ana River, 7–11 Oct 1946, J. L. Sperry (4, 1; USNM Tehama Co., Battle Creek Campground, S fork, 12 Aug 1977, P. H. Arnaud, Jr. (1; CAS Colorado: Jefferson Co., Foxton, 18 Oct 1881 (1; ANSP Larimer Co., Fort Collins, 23 May–21 Aug, 1926–1941, R. H. Beamer, M. T. James (1, 1; KU, USNM Iowa: Story Co., Ames, Izaak Walton League Lake, 23 Apr 1962, D. L. Deonier (1; DLD Michigan: Kalamazoo Co., Gull Lake Biological Station, 22 Jul 1963, R. L. Fischer (1; USNM Montana: Lake Co., Ronan, 3 mi S, 30 Jun–17 Aug 1971, B. A. Foote (6, 14; KSU, USNM), Ronan, 3.2 mi S, 8 Aug 1972, W. N. Mathis (1; USNM), Ronan, 5 mi S, 1–20 Jul 1973, B. A. Foote (7, 5; KSU Sheridan Co., Medicine Lake, 9 Jun 1969, W. W. Wirth (1; USNM Nebraska: Cherry Co., Big Alkali Lake, 2 Jun 1969, W. W. Wirth (2; USNM New Mexico: Catron Co., Glenwood, 1 Jun 1972, W. W. Wirth (1; USNM Dona Ana Co., Las Cruces, 14 Jun 1917, J. M. Aldrich (1; USNM Hildalgo Co., Cienega Lake, 15 mi N Rodeo, 30 Jul 1965, H. B. Leech (1; USNM North Dakota: Burleigh Co., Long Lake, 4 Jun 1969, W. W. Wirth (1; USNM Oregon: Harney Co., Burns, 20 Jul 1962, K. Goeden (2, 2; USNM), Crane Hot Springs, 8 Mar–24 May 1975, W. N. Mathis (1, 1; USNM), Harney Lake, south shore, 16 Jun 1972, W. N. Mathis (2; USNM Klamath Co., Klamath Falls, 31 May 1964, J. Schuh (2; WSU Lake Co., Ana Reservoir, 24 Sep 1971, W. N. Mathis (1; USNM), Summer Lake, 4.8 mi N, 11 Jul 1974, W. N. Mathis (3, 3; USNM South Dakota: Mellette Co., Little White River, 4 Jun 1969, W. W. Wirth (1; USNM Utah: Piute Co., Kingston, 3 Jul 1938, G. F. Knowlton (1, 1; ANSP Utah Co., Goshen Pond, 1 Feb–27 Apr, 1968–1969, W. N. Mathis (17, 7; USNM Washington: Benton Co., Prosser, Irrigation Experiment Station, 17 Aug 1957, W. Cone (1; WSU Grant Co., Soda Lake near O'Sullivan Dam, Columbia Wildlife Refuge, 19 Mar 1977, R. Zack (2, 2; USNM, WSU); O'Sullivan Dam, 4–5 May 1956, H. G. Davis (1, 1; WSU San Juan Co., Olga, 26 Jul 1909 (1; ANSP Whitman Co., Almota, 3 Mar 1977, W. J. Turner (1; WSU), Pullman, 25 Mar–11 Sep, 1971–1976, W. J. Turner, R. S. Zack (1, 1; WSU Wyoming: Bighorn Co., Shell Creek, S Shell Canyon, 24 Jun 1964, H. B. Leech (1; CAS

DISTRIBUTION (Figure 125—North America, primarily in the West, between 85° and 124° west longitude and 31° to 51° north latitude. This species is the most widespread of the pacifica group.

NATURAL HISTORY.—Like most species of this species group, specimens of S. pacifica occur mostly in association with lentic aquatic systems but with one major difference—there appears to be a preference toward alkaline water (Foote, 1982 I have also collected several adults from algal mats on the surface of the pooled effluent of thermal springs in Oregon (Crane Hot Spring) and Utah (Goshen Ponds

Foote's (1982) study of S. atrovirens has extensive notes on S. pacifica. Like the former species, a generation can be completed in 25 to 30 days during the warm season, with divisions among stadia as follows:

Egg incubation

2.3 days

Larval period (3 instars)

10 days

Pupal period

7 days

Adult preoviposition period

6–9 days

Foote studied this species at highly alkaline ponds near Ninepipes Wildlife Refuge, south of Ronan, Montana. The ponds had large quantities of carbonate and bicarbonate ions, and the pH averaged above nine.

Both eggs and larvae were abundant in floating algal mats comprised mostly of Anabaena and Oscillatoria. Larvae were also found in a mat of primarily Rhyzoclonium, a filamentous green alga, the diatom genera Navicula and Synedra, and the desmid genera Closterium, Cosmarium, and Staurastrum. Cells of Cosmarium, among others, were found in the gut of 2nd- and 3rd-instar larvae.

As in S. atrovirens, the puparia of S. pacifica are attached by their hindmost prolegs to pieces of aquatic macrophytes and occasionally to filaments of algae. Also like S. atrovirens, the puparial attachment was frequently below the water's surface, as much as 10 cm.