Stethusa dichroa Gravenhorst 1802
Creators: name: Gusarov, Vladimir I.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Stethusa
Stethusa dichroa

description: Stethusa dichroa (Gravenhorst, 1802)
(Figs. 1­19, 22­42)
Aleochara dichroa Gravenhorst, 1802: 186.
Homalota dichroa: Erichson, 1839: 107 (as valid species). Atheta (Metaxya) dichroa: Bernhauer, 1907: 385 (as valid species). Atheta dichroa: Blatchley, 1910: 353 (as valid species). Atheta (Stethusa) affluens Casey, 1910: 5, syn. nov.
Atheta (Stethusa) irvingi Casey, 1910: 5, syn. nov.
Atheta (Stethusa) galvestonica Casey, 1910: 6, syn. nov. Atheta (Stethusa) canonica Casey, 1910: 6, syn. nov.
Atheta (Stethusa) sagax Casey, 1910: 7, syn. nov.
Atheta (Stethusa) sororella Casey, 1910: 7, syn. nov.
Dimetrota (s. str.) novella Casey, 1910: 105, syn. nov.
Dimetrota (s. str.) sentiens Casey, 1910: 105, syn. nov.
Atheta (Stethusa) clarescans Casey, 1911a: 77, syn. nov. Atheta (Stethusa) irvingi: Casey, 1911a: 78 (as valid species). Atheta (Stethusa) irvingi affluens: Casey, 1911a: 78 (as subspecies or variety of At. irvingi). Atheta (Stethusa) videns Casey, 1911a: 78, syn. nov.
Atheta (Stethusa) cynica Casey, 1911a: 78, syn. nov.
Atheta (Stethusa) cernens Casey, 1911a: 79, syn. nov.
Atheta (Stethusa) officiosa Casey, 1911a: 79, syn. nov.
Atheta (Stethusa) tuta Casey, 1911a: 80, syn. nov.
Atheta (Stethusa) sororella: Casey, 1911a: 80 (as valid species). Atheta (Stethusa) irvingi: Casey, 1911b: 251 (as valid species).
Atheta (Stethusa) affluens: Casey, 1911b: 251 (as "a variety or perhaps less" of At. irvingi).
Atheta (Metaxya) dichroa: Fenyes, 1920: 199 (as valid species).
Atheta (Hypatheta) irvingi: Fenyes, 1920: 207 (as valid species).
Atheta (Hypatheta) affluens: Fenyes, 1920: 207 (as synonym of At. irvingi).
Atheta (Hypatheta) galvestonica: Fenyes, 1920: 207 (as valid species).
Atheta (Hypatheta) canonica: Fenyes, 1920: 207 (as valid species).
Atheta (Hypatheta) sagax: Fenyes, 1920: 207 (as valid species).
Atheta (Hypatheta) sororella: Fenyes, 1920: 207 (as valid species).
Atheta (Dimetrota) novella: Fenyes, 1920: 205 (as valid species).
Atheta (Dimetrota) sentiens: Fenyes, 1920: 205 (as valid species).
Atheta (Hypatheta) clarescans: Fenyes, 1920: 208 (as valid species).
Atheta (Hypatheta) videns: Fenyes, 1920: 208 (as valid species).
Atheta (Hypatheta) cynica: Fenyes, 1920: 208 (as valid species).
Atheta (Hypatheta) cernens: Fenyes, 1920: 208 (as valid species).
Atheta (Hypatheta) officiosa: Fenyes, 1920: 208 (as valid species).
Atheta (Hypatheta) tuta: Fenyes, 1920: 208 (as valid species).
Atheta (Metaxya) dichroa: Bernhauer & Scheerpeltz, 1926: 613 (as valid species).
Atheta (Hypatheta) irvingi: Bernhauer & Scheerpeltz, 1926: 653 (as valid species).
Atheta (Hypatheta) affluens: Bernhauer & Scheerpeltz, 1926: 653 (as synonym of At. irvingi).
Atheta (Hypatheta) galvestonica: Bernhauer & Scheerpeltz, 1926: 653 (as valid species).
Atheta (Hypatheta) canonica: Bernhauer & Scheerpeltz, 1926: 652 (as valid species).
Atheta (Hypatheta) sagax: Bernhauer & Scheerpeltz, 1926: 654 (as valid species).
Atheta (Hypatheta) sororella: Bernhauer & Scheerpeltz, 1926: 654 (as valid species).
Atheta (Dimetrota) novella: Bernhauer & Scheerpeltz, 1926: 664 (as valid species).
Atheta (Dimetrota) sentiens: Bernhauer & Scheerpeltz, 1926: 665 (as valid species).
Atheta (Hypatheta) clarescans: Bernhauer & Scheerpeltz, 1926: 653 (misspelled as At. clarescens; as valid species).
Atheta (Hypatheta) videns: Bernhauer & Scheerpeltz, 1926: 655 (as valid species).
Atheta (Hypatheta) cynica: Bernhauer & Scheerpeltz, 1926: 653 (as valid species).
Atheta (Hypatheta) cernens: Bernhauer & Scheerpeltz, 1926: 653 (as valid species).
Atheta (Hypatheta) officiosa: Bernhauer & Scheerpeltz, 1926: 654 (as valid species).
Atheta (Hypatheta) tuta: Bernhauer & Scheerpeltz, 1926: 654 (as valid species).
Atheta dichroa: Blackwelder, 1943: 552 (as valid species).
Atheta dichroa: Blackwelder, 1944: 160 (as valid species).
Atheta (Brundinia) dichroa: Moore & Legner, 1975: 359.
Atheta (Stethusa) irvingi: Moore & Legner, 1975: 364 (as valid species).
Atheta (Stethusa) affluens: Moore & Legner, 1975: 364 (as synonym of At. irvingi).
Atheta (Stethusa) galvestonica: Moore & Legner, 1975: 362 (as valid species).
Atheta (Stethusa) canonica: Moore & Legner, 1975: 356 (as valid species).
Atheta (Stethusa) sagax: Moore & Legner, 1975: 373 (as valid species).
Atheta (Stethusa) sororella: Moore & Legner, 1975: 374 (as valid species).
Atheta (Dimetrota) novella: Moore & Legner, 1975: 367 (as valid species).
Atheta (Dimetrota) sentiens: Moore & Legner, 1975: 373 (as valid species).
Atheta (Stethusa) clarescans: Moore & Legner, 1975: 357 (misspelled as At. clarescens; as valid species).
Atheta (Stethusa) videns: Moore & Legner, 1975: 377 (as valid species).
Atheta (Stethusa) cynica: Moore & Legner, 1975: 358 (as valid species).
Atheta (Stethusa) cernens: Moore & Legner, 1975: 356 (as valid species).
Atheta (Stethusa) officiosa: Moore & Legner, 1975: 368 (as valid species).
Atheta (Stethusa) tuta: Moore & Legner, 1975: 376 (as valid species).
Dimetrota novella: Seevers, 1978: 259 (as valid species). Dimetrota sentiens: Seevers, 1978: 259 (as valid species). Philhygra dichroa: Seevers, 1978: 266 (as valid species). Stethusa irvingi: Seevers, 1978: 267 (as valid species).
Stethusa affluens: Seevers, 1978: 267 (as synonym of S. irvingi). Stethusa galvestonica: Seevers, 1978: 267 (as valid species). Stethusa canonica: Seevers, 1978: 267 (as valid species). Stethusa sagax: Seevers, 1978: 267 (as valid species).
Stethusa sororella: Seevers, 1978: 267 (as valid species). Stethusa clarescans: Seevers, 1978: 267 (as valid species). Stethusa videns: Seevers, 1978: 267 (as valid species).
Stethusa cynica: Seevers, 1978: 267 (as valid species).
Stethusa cernens: Seevers, 1978: 267 (as valid species).
Stethusa officiosa: Seevers, 1978: 267 (as valid species). Stethusa tuta: Seevers, 1978: 267 (as valid species).
Atheta dichroa: Pace, 1985: 454 (as valid species).
Atheta dichroa: Klimaszewski & Peck, 1998: 241 (as valid species).
Type material. Lectotype of Aleochara dichroa (here designated): ɗ, "Americ.[a] Sept.[entrionalis] Zimmermann Nr. 5423" (green label), " Typus " (red label), "Zool. Mus. Berlin", " Aleochara dichroa Grav. Lectotypus Lohse fix. 1983" (Lohse did not publish this lectotype designation), " Atheta dichroa (Gr.) det. R. Pace 1983" (ZMHB); Paralectotypes: ɗ, "5423", " dichroa Gr. Am. [erica] Spt.[Septentrionalis] Zimm.[ermann]" (green label), " Typus " (red label), "Zool. Mus. Berlin"; ɗ, "Americ.[a] sept.[entrionalis] Zimmermann Nr. 5423" (green label), " Typus " (red label), "Zool. Mus. Berlin"; Ψ, " dichroa Er. Typ. ", "Americ.[a] sept.[entrionalis] Zimmermann Nr. 5423" (green label), " Typus " (red label), "Zool. Mus. Berlin" (ZMHB).
Lectotype of Atheta affluens (here designated): ɗ, "R. I. [Rhode Island, Boston Neck]", " affluens Csy. ", " TYPE USNM 39440" (red label), " CASEY bequest 1925" (NMNH). Paralectotypes: ɗ, 3ΨΨ, "R. I. [Rhode Island, Boston Neck]", "? affluens PARATYPE USNM 39440" (red label), " CASEY bequest 1925"; ɗ, "L.[ong] I.[sland]", "? affluens PARATYPE USNM 39440" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta irvingi (here designated): ɗ, "N.Y. [New York, Catskill Mts.]", " irvingi Csy. ", " TYPE USNM 39438" (red label), " CASEY bequest 1925" (NMNH). Paralectotypes: 8ɗɗ, 7ΨΨ, "N.Y. [New York, Catskill Mts.]", " CASEY determ. irvingi ", " CASEY bequest 1925" (NMNH).
Lectotype of Atheta galvestonica (here designated): Ψ, "Tex. [Texas, Galveston]", " galvestonica Csy. ", " TYPE USNM 39443" (red label), " CASEY bequest 1925" (NMNH). Paralectotype: Ψ, "Tex. [Texas, Galveston]", " galvestonica PARATYPE USNM 39443" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta canonica (here designated): ɗ, "R. I. [Rhode Island, Boston Neck]", " canonica Csy. ", " TYPE USNM 39445" (red label), " CASEY bequest 1925" (NMNH). Paralectotype: Ψ, "R. I. [Rhode Island, Boston Neck]", " canonica PARATYPE USNM 39445" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta sagax (here designated): ɗ, "Va. [Virginia, Norfolk]", " sagax Csy. ", " TYPE USNM 39447" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta sororella (here designated): ɗ, "N.Y. [New York, Catskill Mts.]", " sororella Csy. ", " TYPE USNM 39452" (red label), " CASEY bequest 1925" (NMNH). Paralectotype: Ψ, "N.Y. [New York, Catskill Mts.]", " sororella PARATYPE USNM 39452" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Dimetrota novella (here designated): Ψ, "L. I. [Long Island, Willets Point]"; " novella Csy. ", " TYPE USNM 39124" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Dimetrota sentiens (here designated): Ψ, "Onaga, 8/13/03 [13.viii.1903; Kansas (Warren Knaus)]", " sentiens Csy. ", " TYPE USNM 39125" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta clarescans (here designated): ɗ, "N.Y. [New York, Catskill Mts.]", " clarescans Csy. ", " TYPE USNM 39441" (red label), " CASEY bequest 1925" (NMNH). Paralectotype: Ψ, "N.Y. [New York, Catskill Mts.]", " clarescans PARATYPE USNM 39441" (red label), " CASEY bequest 1925" (NMNH).
Holotype of Atheta videns: Ψ, "R. I. [Rhode Island, Boston Neck]", " videns Csy. ", " TYPE USNM 39448" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta cynica (here designated): Ψ, "R. I. [Rhode Island, Boston Neck]", " cynica Csy. ", " TYPE USNM 39449" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta cernens (here designated): ɗ, "Miss.[issippi; Pass Christian]", " cernens Csy. ", " TYPE USNM 39442" (red label), " CASEY bequest 1925" (NMNH). Paralectotype: Ψ, "Miss.[issippi; Pass Christian]", " cernens PARATYPE USNM 39442" (red label), " CASEY bequest 1925" (NMNH).
Lectotype of Atheta officiosa (here designated): ɗ, "N.Y. [New York, Catskill Mts.]", " officiosa Csy. ", " TYPE USNM 39450" (red label), " CASEY bequest 1925" (NMNH).
Holotype of Atheta tuta: ɗ, "N.Y. [New York, Ithaca]"; " tuta Csy. ", " TYPE USNM 39451" (red label), " CASEY bequest 1925" (NMNH).
Additional material. UNITED STATES: ɗ, without locality data (FMNH); Maine: 2ɗɗ, 13ΨΨ, without locality data (Frost) (CASC, FMNH); Vermont: 2 specimens, without locality data (FMNH); Massachusetts: Norfolk Co.: Ψ, Dover, v (CASC); ɗ, Milton (Wickham), 2.vi.1901 (CASC); Suffolk Co.: ɗ, Dorchester (Wickham), 11.vi.1905 (CASC); Middlesex Co.: 5ɗɗ, 4ΨΨ, Framingham (Frost) (CASC, FMNH); Bristol Co.: ɗ, Somerset (N.S.Easton) (CASC); Connecticut: Tolland Co.: Ψ, Stafford, 24.viii.1905 (W.E.Britton) (NMNH (Casey Collection)); New York: Ulster Co.: ɗ, "N.Y. [Catskill Mountains, Shokan (according to Casey locality Code (FitzGerald 1962)]"; Tompkins Co.: ɗ, 3ΨΨ, "N.Y." (with three black dots under the letters) [Ithaca]; Queens: 2ΨΨ, "L.I." [Willets Point] (NMNH (Casey Collection)); New Jersey: Ψ, without locality data (Luetgens), 13.ix.1891 (CASC); Cape May Co.: ɗ, Anglesea (NMNH (Casey Collection)); Middlesex Co.: Ψ, Avenel (FMNH); Pennsylvania: Westmoreland Co.: 1 specimen, 2ɗɗ, 4ΨΨ, Jeannette (H.G.Klages) (CASC, FMNH); ɗ, 2ΨΨ, ditto but vii (CASC); 4ɗɗ, 8ΨΨ, 1 specimen, ditto but viii (CASC, FMNH); Ohio: Hamilton Co.: ɗ, Cincinnati (Dury) (CASC); Illinois: McHenry Co.: Ψ, Algonquin (W.A.Nason) (CASC); Pope Co.: 7 specimens, 2 km N Eddyville, Shawnee National Forest, 37º33.58'N 88º34.95'W, 200m, in horse dung, 29.viii.1999 (V.I.Gusarov) (KSEM, SPSU); Maryland: ɗ, Ψ, Baltimore (FMNH); ɗ, Ψ, ditto but (F.E.Blaisdell), 10.vi.1909 (CASC); Virginia: Page Co./ Madison Co.: 2ɗɗ, 4ΨΨ, Shenandoah National Park, Stony Man Mt. (S.Peck), 10.iv.1967 (FMNH); West Virginia: Greenbrier Co.: 3ɗɗ, 2ΨΨ, White Sulphur Springs, vii (CASC, FMNH); North Carolina: Buncombe Co.: 2ɗɗ, "·N.C." [Asheville] (NMNH (Casey Collection)); South Carolina: Pickens Co.: Ψ, Table Rock State Park, 11.vii.1988 (J.K.Moulton) (KSEM); Missouri: 8 specimens, no locality data (ZMHB, FMNH); Iowa: Johnson Co.: ɗ, Iowa City (Wickham) (FMNH); Kansas: Jefferson Co.: 8 specimens, 12 km NNE Lawrence, 39º04.57'N 95º11.88'W, in cow dung, 250m, 8.vi.1999 (V.I.Gusarov) (KSEM, SPSU); Douglas Co.: ɗ, 3ΨΨ, 1.5 km N Lawrence, right bank of the Kansas River, 38º58.96'N 95º14.62'W, in heaps of rotting wood chips, 200m, 1.v.1999 (V.I.Gusarov); 5 specimens, 18 km SSE Lawrence, Breidenthal Preserve, 38º48.50'N 95º11.52'W, on rotting fruits of Asimina triloba, 250m, 3.x.2000 (V.I.Gusarov); 2 specimens, ditto but flight intercept traps baited with beer, 15­18.iv.2002 (all ­ SPSU); Arkansas: Pulaski Co.: ɗ, Little Rock (Wickham) (NMNH (Casey Collection)); Searcy Co.: 4ɗɗ, Ψ, Ozark National Forest, Forest Road 1205, Richland Creek, ex cow dung (J.M.Campbell), 15.v.1986 (CNCI; SPSU); Louisiana: St. Landry Parish: ɗ, Opelousas, v (Klages) (FMNH); 2ɗɗ, ditto but vi (CASC); East Baton Rouge Co.: ɗ, 2ΨΨ, Baton Rouge, Louisiana State University campus, light traps, 7­17.v.1998 (A.Tishechkin) (SPSU); Alabama: Mobile Co.: 5ΨΨ, Mobile (Loding) (CASC); Florida: Osceola Co.: 5ɗɗ, Ψ, 3 mi. SW Lake Marian, caracara nest (Howden & Howell), 15.iii.1956 (CNCI; SPSU); Brevard Co.: ɗ, Cocoa (H.F.Howden), 12.iii.1956 (CNCI); FRANCE: Guadeloupe: 2ɗɗ, no locality data (FMNH); GRENADA: ɗ, St. John's Riv. (Leeward side), [18]86 [?] (H.H.Smith) (FMNH); PARAGUAY: Ψ, no locality data (Drake) (FMNH); ECUADOR: Galápagos Islands: 13 specimens, Isla San Cristóbal, 1 km E El Junco, Miconia ravine litter, 550 m, 14.ii.1989 (S.Peck) (FMNH).
Diagnosis. Stethusa dichroa is distinguished from two other Nearctic species of the genus by the terminal antennal article with two subbasal impressions covered with dense microsetae; the distinct shape of the male tergum 8 (Figs. 22, 24­26); the shape of aedeagus (Figs. 29­39), particularly the presence of two distal spines of the internal sac (Figs. 34, 37­38); the shape of the spermatheca (Figs. 41­42); and the presence of a quadrangular female accessory sclerite (Fig. 40).
Stethusa dichroa differs from the Neotropical S. luederwaldti by a larger body size; the shape of the aedeagus (Figs. 29­39; 76­82); the presence of two distal spines of the internal sac (Figs. 34, 37­38; 80­81); the shape of the spermatheca (Figs. 41­42; 83); and the presence of a female accessory sclerite (Fig. 40).
Stethusa dichroa is distinguished from the Neotropical S. lurida by the shape of the spermatheca (Figs. 41­42: this paper; Fig. 46: Klimaszewski & Peck 1998).
Description. Length 2.0­3.0 mm. Head and abdomen dark brown to black, pronotum brown, elytra brownish yellow with darker area around scutellum, legs yellow, mouthparts and antennae brown, first and often second antennal segments yellowish.
Head surface glossy, with weak isodiametric microsculpture, with fine punctation, distance between punctures equals 2 times their diameter. Eyes very large, 3.5­4.5 times as long as temples. Antennal article 2 is 1.1 times as long as article 3, article 4 subquadrate, 5­9 slightly elongate, 10 subquadrate, article 11 as long as articles 9 and 10 combined (Fig. 16). The terminal antennal article with two subbasal impressions covered with dense microsetae.
Pronotum transverse, 1.3 times as wide as head, width 0.54­0.69 mm, length 0.41­0.53 mm, width to length ratio 1.3; glossy, with very weak isodiametric microsculpture (hardly visible at 70x); punctation as fine as on head but denser, distance between punctures equal to 1­2 times their diameter. Elytra much wider (0.67­0.84 mm) and longer (0.50­0.61 mm; measured from humeral angle) than pronotum (elytral length to pronotal length ratio 1.2), 1.4 times wider than long, surface glossy, without visible (at 70x) microsculpture; punctation as on pronotum, slightly asperate.
Abdominal terga glossy, with weak microsculpture consisting of transverse waves; with fine punctation, distance between punctures equals 1­3 times their diameter on terga 3­5 and 2­5 times on terga 6­7. Apical margin of tergum 7 with white palisade fringe.
Male tergum 7 without medial tubercle in front of posterior margin. Posterior margin of male tergum 8 with two blunt medial projections and two lateral denticles (Figs. 22, 24­ 26).
Aedeagus as in Figs. 29­39, internal sac with two distal spines (Figs. 34, 37­38). Females with quadrangular accessory sclerite (Fig. 40). Spermatheca as in Figs. 41­ 42, the distal portion is bent towards the side bearing the spermathecal gland.
Discussion. Stethusa dichroa varies in body size, but the shape of the aedeagus and the spermatheca are the same in small and large specimens. As in many other aleocharine genera the denticles at the posterior margin of male tergum 8 are longer in larger males (Figs. 24­26). Casey (1910, 1911a) failed to recognize the variability of this character and some of his Stethusa species were based entirely on the different size of these denticles. The types of all species synonymized here with S. dichroa fall within the range of variability of that species.
Distribution. Widely distributed in the eastern United States (Fig. 110). The record from Pasadena, California (Bernhauer 1907) is a misidentification (ɗ, "Pasadena Cal. Dr. A.Fenyes", " dichroa Er.? det. Bernhauer", "Chicago NHMus. M.Bernhauer Collection" (FMNH; examined). Stethusa dichroa is also known from Bolivia (Pace 1985), Brasil (Blackwelder 1943), Paraguay, the Galápagos Islands and the Antilles (St. Thomas (Pace 1985), Tortola, St. Vincent (Blackwelder 1943), Grenada and Guadeloupe).
Considering the wide distribution of this species it might be interesting to discuss the possibility that S. dichroa was introduced to some parts of its current range. The fact that S. dichroa is not known from the western United States is significant in that this species is common in dung and would not have been overlooked by collectors working on the West Coast. If S. dichroa was introduced from South America, it is difficult to imagine it was established in North America as early as 1802 (Gravenhorst 1802) and as far North as Maine but that it failed to spread to the West Coast. An alternative hypothesis of S. dichroa being introduced to South America seems more plausible. To test this hypothesis, it would be important to determine whether S. dichroa occurs in natural habitats in South America or restricted to human settlements.
Based on an examination of extensive material obtained during 15 months of work on the Galápagos Islands, Klimaszewski and Peck (1998) concluded that S. dichroa was the most common aleocharine species on the islands. They incorrectly stated that the type series of S. dichroa came from South America and the island of St. Thomas in the West Indies (Klimaszewski & Peck 1998: 242). In fact, the species was described from North America (Gravenhorst 1802) without mention of the exact locality. Klimaszewski and Peck (1998) also judged S. dichroa to be native to the Galápagos Islands without explicitly stating why. Considering that the Galápagos specimens of S. dichroa are identical to the continental specimens in all characters, including the details of male and female genitalia, and the fact that the islands are isolated from the closest landmass by a gap of about 1000 km, recent introduction by humans seems to be a more likely explanation for the presence of S. dichroa on the islands.
Natural History. Stethusa dichroa is common in dung, and other kinds of decomposing organic matter.
description: Published as part of Gusarov, Vladimir I., 2003, A revision of the Nearctic species of the genus Stethusa Casey, 1910 (Coleoptera: Staphylinidae: Aleocharinae), pp. 1-43 in Zootaxa 239 on pages 12-21, DOI: 10.5281/zenodo.156493