Comprehensive Description
provided by Smithsonian Contributions to Zoology
Setacera atrovirens (Loew)
Figures 3–12
Ephydra atrovirens Loew, 1862:169.—Osten Sacken, 1878:203 [nearctic catalog].—Aldrich, 1905:629 [nearctic catalog].
Setacera atrovirens.—Cresson, 1930:116 [listing].—Johannsen, 1935:53 [description of immature stages].—Wirth, 1965:755 [nearctic catalog, in part].
Setacera atrovierns [sic].—Sturtevant and Wheeler, 1954:202, 203 [key and locality data].
DESCRIPTION.—Medium-sized to moderately large shore flies, length 3.5 to 4.7 mm; dorsum dark olivaceous brown to green, becoming duller, grayer ventrally.
Head (Figures 3–5): Head width-to-height ratio averaging 1 : 0.68; frons width-to-length ratio averaging 1 : 0.48; mesofrons, fronto-orbits, and dorsum of interfoveal carina deep bluish green to mostly bluish, dorsum of interfoveal carina frequently sparsely tomentose; dorsal surface of face shorter than height of anterior surface; angle formed by anterior surface and dorsal surface obviously obtuse, about 135° anterior surface of face usually lightly yellowish brown, especially dorsally, sometimes becoming almost whitish ventrally. Eye height-to-width ratio averaging 1 : 0.95; eye-to-cheek ratio averaging 1 : 0.40.
Thorax: Costal vein ratio averaging 1 : 0.29; M1+2 vein ratio averaging 1 : 0.79.
Abdomen: Male terminalia (Figures 6–9) with epandrium usually poorly sclerotized dorsally if at all evident; surstyli with lateral margin more or less evenly rounded, not angulate, median surfaces separated, distance approximately equal to surstylar width in posterior view, with pointed projection medially between surstyli toward base. Female terminalia (Figures 10, 11) as in species-group description.
TYPE MATERIAL.—The male lectotype, herein designated, is labeled “Mittel St. [mid-Atlantic states of the United States]/Loew Coll[ection]./ atrovirens/50/Type 11179 [red].” The lectotype is in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, type number 11179.
OTHER SPECIMENS EXAMINED.—CANADA. Nova Scotia: Petite Riviere, 2 Jul 1935, J. McDunnough (1; CNC Ontario: Black Sturgeon Lake, 28 Jun 1962 (1; CNC); Grand Bend, 8 Jul 1939, G. E. Shewell (1; CNC); Guelph, 1 Nov 1955, J. R. Vockeroth (1; CNC); Kingston, 10 Jul 1938, A. L. Melander (1; USNM); Ottawa, 25 Apr-30 Jul, 1922–1965, A. R. Brooks, C. H. Curran, J.E.H. Martin (15, 49; ANSP, CNC); Ottawa, Mer Bleue, 26 May 1923, C.H. Curran (1; ANSP Quebec: Abbotsford, 1 Jul-26 Sep, 1935–1936, G. E. Shewell (2; CNC); Old Chelsea, 9 Oct 1955, J. R. Vockeroth (1; CNC UNITED STATES. Delaware: Sussex Co., Rehoboth, 25 Jun 1939, A. L. Melander (1; USNM District of Columbia: A. L. Melander (1; USNM Illinois: Mason Co., Havana, river shore, 16 Nov 1913 (1; ANSP McHenry Co., 21 Aug 1903, 1927, A. L. Melander (4, 2; ANSP, USNM Indiana: LaGrange Co., Pigeon River Fish and Wildlife Area, 30 Jul 1977, M. Minno (1, 2; USNM Iowa: Boone Co., Boone, 1.5 mi W, 4 Aug 1960, D. L. Deonier (1; DLD); Ledges State Park, 30 Jul 1971, R. M. Miller (1; USNM); Little Wall Lake, 14 Jul–22 Sep, 1960–1962, D. L. Deonier (14, 13; DLD Greene Co., Spring Lake Recreational Reserve, 19 Sep 1961, D. L. Deonier (5; DLD Hamilton Co., Goose Lake, 2 Jul 1961, D. L. Deonier (1; DLD Louisa Co., Lake Odessa, 9 Aug 1960, D. L. Deonier (1, 4; DLD Winneshiek Co., Siewers Spring State Park near Decorah, 9 Sep 1961, D. L. Deonier (1, 1; DLD Kansas: Douglas Co., 900 ft (1; KU Maine: Penobscott Co., Old Town, Lake Pushaw, 1 Aug 1966, W. W. Wirth (1; USNM Michigan: Cheboygan Co., 10 Aug 1932, J. D. Nottingham (1; KU Ingham Co., East Lansing, 27 Jun 1936, C. Sabrosky (1; ANSP Livingston Co., E. S. George Reserve, 24 Jul 1943, G. C. Steyskal (1, 1; USNM Minnesota: Clearwater Co., Itasca State Park, 15 Jun–3 Aug 1937, A. R. Barr, D. Keith, K. C. Kim, M. E. Rueger (13, 43; UMIN Itasca Co., Grand Rapids, 30 Jun 1966, B. C. Ahlm (1, 8 UMIN La Sueur Co., 28 Aug 1923, W. E. Hoffmann (1; UMIN Polk Co., Crookston, 27 Jun 1937, D. G. Denning (1; UMIN Ramsey Co., St. Paul, 22 April 1922, W. E. Hoffmann (1; UMIN Waseca Co., Waseca, 3 Jul-11 Sep, 1941–1967, R. E. Carlson, H. T. Peters (1, 2; UMIN Montana: Lake Co., Polson, 2.3 mi E, 24 Jul 1973, B. A. Foote (2, 1; KSU Nebraska: Cherry Co., Pelican Lake, 2 Jun 1969, W. W. Wirth (2; USNM New York: Jefferson Co., Picton Island, Clayton, 18 Aug 1960, B. Heineman (1; AMNH Tompkins Co., Keyden Lake, 8 Aug 1961, D. L. Deonier (4, 2; DLD); Ithaca, 4 Sep 1973 (2; CU); McLean Reserve, 29 Mar 1962, L. V. Knutson (1; CU North Dakota: Burleigh Co., Long Lake, 4 Jun 1969, W. W. Wirth (2; USNM Ramsey Co., Devils Lake, 5 Jun 1969, W. W. Wirth (1; USNM Ohio: Portage Co., Kent, 9 Apr 1969, R. Miller (1; KSU); Kent, 1 mi E, 11 Sep 1972, B. A. Foote (40; KSU); Kent, 4.5 mi E, 1 May 1969, W. Eastin (1; KSU); Ravenna, 15 mi E, 28 Sep-11 Oct 1971, B. A. Foote (1, 3; KSU Wayne Co., Rittman, 0.5 mi S, 18 Sep 1969, B. A. Foote (1, 2; KSU South Dakota: Hand Co., Burdette, 20 Jul 1937, R. H. Beamer (1; KU Wisconsin: Dane Co., 20 Jul 1900 (2; USNM
DISTRIBUTION (Figure 12.)—East central North America, primarily around the Great Lakes, between 55° and 105° west longitude and 38° and 49° north latitude.
NATURAL HISTORY.—Foote (1979; 1982) has recently published detailed studies on the life history and immature stages of S. atrovirens. In particular, he reported the feeding preferences of this species, using both field and laboratory studies. Most of the information to follow is paraphrased from his observations and analysis.
The life cycle of S. atrovirens takes approximately 25 days and is divided among the stadia as follows:
Egg incubation
2.3 days
Larval period (3 instars)
10 days
Pupal period
7 days
Adult preoviposition period
6–9 days
The fly apparently overwinters as an adult, probably in a state of reproductive diapause. During the warm season, from May to September in the northern states, four or more generations are produced.
In the field, Foote discovered eggs in floating mats of primarily blue-green algae. Along the marshy shores of Flathead Lake, Montana, the fly preferred growths of Nostoc, but near Kent, Ohio, they were usually found in mats of Oscillatoria or a mixed mat of Anabaena and Spirogyra. Foote's laboratory experiments showed that larvae of this species would develop readily in algae of the genera Anabaena, Cylindrospermum, Lyngbya, Nostoc, and Navicula. In contrast, however, larvae were apparently unable to use species of Anacystic, Gloeocapsa, and Chlorella. Interestingly, utilization experiments between two species of Oscillatoria clearly showed that larvae of S. atrovirens can discriminate between the two algal species. Foote found that 80% of the larvae reached the pupal stage when fed O. tenuis, but no larvae formed puparia in cultures of O. chalybea. From larval gut dissections, Deonier (1972) found that the algae ingested by larvae of S. atrovirens included about one-half diatoms and one-half other algae.
In part, larval age also determined food preference. Newly hatched larvae appeared to prefer small unicells, whereas older larvae utilized a broader range of algal species, frequently trichomes of blue-green algae. Larvae can feed completely submerged, but return to the water's surface periodically for respiration.
Just prior to forming puparia, larvae left the algal colonies and sought out stems or narrow leaves of aquatic macrophytes, to which they became attached using the last prolegs. Puparia were frequently formed below the water's surface, and submergence apparently had no effect on subsequent development.
Foote observed several successful attacks on Setacera larvae by larvae of water-scavenger beetles (Hydrophilidae), which are probably the primary predator of the larval stages. Foote also reared a chalcidoid parasitoid from a few field-collected puparia.
- bibliographic citation
- Mathis, Wayne Neilsen. 1982. "Studies of Ephydrinae (Diptera: Ephydridae), VII: Revision of the Genus Setacera Cresson." Smithsonian Contributions to Zoology. 1-57. https://doi.org/10.5479/si.00810282.350