Dineutus assimilis (Kirby, 1837)

Gustafson, Grey T. & Miller, Kelly B., 2015, The New World whirligig beetles of the genus Dineutus Macleay, 1825 (Coleoptera, Gyrinidae, Gyrininae, Dineutini), ZooKeys 476, pp. 1-135 : 26-29

Dineutus assimilis (Kirby, 1837) Figures 8, 9, 52

Cyclinus assimilis Kirby 1837: 78, [ Gyrinus americanus : Fabiricus 1775: 235 misidentified], [ Cyclous americanus : Dejean 1833: 58 misidentified], Dineutes assimilis : Aubé 1838 b: 778, [ Dineutus americanus : LeConte 1863: 18 misidentified], Dineutus assimilis : LeConte 1868: 366, [ Dineutes americanus : Régimbart 1882: 415 misidentified], Dineutes assimilis : Roberts 1895: 285, [ Dineutes americanus : Régimbart 1907: 138 misidentified], Dineutes assimilis : Ahlwarth 1910: 4, [ Dineutes americanus : Zimmermann 1917: 137 misidentified], Dineutes assimilis : Leng and Mutchler 1918: 98, [ Dineutes americanus : Leng 1920: 82 misidentified], Dineutus (Cyclinus) assimilis : Hatch 1925b: 447 subjective synonym, [ Dineutus (Cyclous) americanus : Hatch 1927: 28 misidentified], [ Dineutus americanus : Leng and Mutchler 1927: 18 misidentified], Dineutus assimilis : Ochs 1927b: 36, [ Dineutus americanus : Leonard 1928: 263 misidentified], Dineutus assimilis : Ochs 1930: 135, Dineutus (Cyclinus) assimilis : Hatch 1930: 18, Dineutus assimilis : Gordon and Post 1965: 27, [ Dineutus americanus : Ciegler et al. 2003: 14 misidentified].

Type locality.

"Lat. 54°".

Specimens examined.

273

Type material.

Not examined. Having examined the type for Dineutus americanus , the most confused name with Dineutus assimilis , it seems that the identity of Dineutus assimilis is secure, so no attempt to loan the type was made.

Material examined.

CANADA: Ontario: Kent Co., Tilbury, vi.1960, leg. K. Stephan (1 ex. FSCA). U.S.A.: Alabama: Perry Co., Boguechitto Creek,19.vi.1962, leg. F.N. Young, #2047 (1 ex. FSCA); Monroe Co., 10km W Bowles, 31°33.094'N, 86°59.956'W, 11.v.2006, leg. K.B. Miller, KBM1105063 (1 ex. MSBA); Arkansas: Benton Co., State Fish Hatchery, 12.iv.1974 (1 ex. FSCA); Conway Co., I-40 Rest Area, 181, 9mi W of State Line, 11.v.1983, leg. L.R. Davis Jr., (1 ex. FSCA); Florida: Alachua Co., Gainesville, 17.vi.1947 (1 ex. FSCA); 2 mi NW Gainesville, 20.iv.1974, leg. J.B. Heppner, blacklight (1 ex. FSCA); pond nr. River Styx, 1.viii.1975, leg. J.B. Heppner (1 ex. FSCA); Newman’s Lake, 25.vii.1975, leg. J.B. Heppner (7 ex. FSCA); Columbia Co., O’Leno State Park, 12.ii.1966, leg. F.W. Mead (1 ex. FSCA); Highlands Co., Archbold Biol. Sta., 24.iv.1976, leg. L.L. Lampert Jr. (1 ex. FSCA); Hillsborough Co., 6 mi N Tampa, 3.vi.1978, leg. R. Milton (1 ex. FSCA); Leon Co., SR 373 1 mi SW SR 371, Tallahassee, 16.x.1976 (1 ex. FSCA); Liberty Co., Torreya State Park, 15.v.1970, leg. H. Greenbaum, blacklight/sheet (1 ex. FSCA); Torreya State Park, 25.v.1980, leg. J. Watts, attr. To U.V. (1 ex. FSCA); Georgia: Rabun Co., lake in BRM St. Pk., 2.vii.1982, leg. F.N. Young, #2965 (3 ex. FSCA); Indiana: Brown Co., nr Crooked Creek, 1.x.1977, leg. F.N. Young (1 ex. FSCA); Crawford Co., Grantsburg, 18.vii.1965, leg. D. Eckert, Blacklight trap (3 ex. FSCA); Ford Co., New Albany, 5.vii.1966, leg. C.E. White, Blacklight trap (2 ex. FSCA); Imperanon Co., 18.viii.1987, leg. N.M. Downie (1 ex. FSCA); Johnson Co., Peoga, 6.v.1966, leg. E. White (7 ex. FSCA); Knox Co., White River, nr Kinora, 12.ix.1964, leg. F.N. Young, #2168 (1 ex. FSCA); Slough along White River, at Edwardsport, 15.iv.1960, leg. F.N. Young, #1687 (1 ex. FSCA); Marion Co., Indianapolis, 15.vii.1963, leg. E. White (1 ex. FSCA); Camp Belzer, BSA, Indianapolis, 12.vii.1966, leg. C.E. White (2 ex. FSCA); Monroe Co., Bloomington, 6.v.1953, leg. R.M. Laycock (1 ex. FSCA); Bloomington, 2.vi.1991, leg. F.N. Young, BLT (1 ex. FSCA); Posey Co., Hovey Lake, 15.viii.1965, leg. C.E. White, Blacklight trap (3 ex. FSCA); Iowa: Boone Co., Ledges State Park, 2.v.1955, leg. M.D. Huffman (3 ex. FSCA); same as previous except: 2.v.1985 (1 ex. FSCA); same as previous except: 1.x.1961, leg. J.J. Dinsmore (3 ex. FSCA); same as previous except: 1.xi.1961 (1 ex. FSCA); Linn Co., Cedar Rapids, “1536” (1 ex. MTEC); Plymouth Co., Le Mars, 12.v.1965, leg. B. Perrill (1 ex. FSCA); Story Co., Ames, 15.iv.1930, leg. H.B. Mills (2 ex. MTEC); same as previous except: 24.iv.1939, leg. C. Haight (3 ex. MTEC); Kansas: Douglas Co., Lawrence, 24.ix.1921, leg. C. Brown (2 ex. FSCA); Maryland: Kent Co., Chestertown, 13.v.1969, leg. T.E. Rogers (1 ex. FSCA); Montgomery Co., Seneca, 27.v.1951, leg. G.H. Nelson (2 ex. FSCA); Prince George’s Co., College Park, 17.iv.1948, leg. B.K. Dozier, in pond (2 ex. FSCA); College Park, 29.iv.1948, leg. H.L. Dozier (1 ex. FSCA); College Park, 14.x.1948, leg. R. Mansueti (1 ex. FSCA); College Park, 25.iv.1953, leg. G.H. Nelson, to light (1 ex. FSCA); Massachusetts: Norfolk Co., Dedham, 11.vi.1920 (1 ex. FSCA); Minnesota: Morner Co., nr Grand Meadow, roadside park, 18.viii.1965, leg. R.H. Arnett, in dammed pond (13 ex. FSCA); Morula Co., nr Grand Meadow, 18.viii.1965, leg. R.H. Arnett Jr., roadside park in damned pond (40 ex. FSCA); Mississippi: Marshall Co., Byhalia, 10.v.1983, leg. L.R. Davis Jr., 11:15PM at lights (1 ex. FSCA); Missouri: Calloway Co., 3 mi W Portland on Rt 94, temp pool, 12.vii.1973, leg. S.O. Swadener, Lot No.730712A (1 ex. FSCA); Carter Co., Van Buren, 22.vi.1955 (2 ex. FSCA); Clay Co., nr Missouri River, E of Birmingham, 2.v.1968, leg. J.R. Heitzman (1 ex. FSCA); Dent Co., Montauk St. Pk., 18.v.1978, leg. S.O. Swadener, Lot No.730518-A (1 ex. FSCA); Douglas Co., Cartwright Tree Farm, 10 mi E of Cabool, walnut, apple, & peach orchards, Deciduous Ozark Forest, open fields & Indian Creek, 14.vii.1991, leg. H.M. Webber, at U.V. light (1 ex. FSCA); Franklin Co., 3.vii.1978, leg. K. Jackson, in lake (1 ex. FSCA); same as previous except: at light (1 ex. FSCA); Green Co., Willard, 6.vii.1929, leg. K. Nime, pond (1 ex. FSCA); Jackson Co., Adair Park, Independence, 3.v.1968, leg. J.R. Heitzman (1 ex. FSCA); Vernon Co., Nevada, 10.v.1964, leg. D&J. McReynolds, (1 ex. FSCA); same as previous except: 8.vi.1964 (1 ex. FSCA); same as previous except: 9.v.1972, leg. J.W. McReynolds (1 ex. FSCA); Montana: Wibaux Co., pond 30 mi N Wibaux, 27.vii.1990, leg. D.L. Gustafson (2 ex. MTEC); Nebraska: Cherry Co., McKelvie Nat’l For., 30 mi WSW Valentine, 9.vii.1998, leg. A. Ramsdale, at blacklight, at forest margin near sand hills prairie, night (1 ex. MTEC); New Jersey: Gloucester Co., Paulsboro, 11.vi.1961, leg. H.L. Dozier (1 ex. FSCA); Ocean Co., Lakehurst, 1.viii.1960, leg. H.L. Dozier (1 ex. FSCA); New York: Schuyler Co., Texas Hollow State Wildlife Area, 1.ix.1999, leg. K.B. Miller (5 ex. MSBA); Westchester Co., White Plains, 14.v.1922, leg. E.H.P. Squire, (1 ex. FSCA); same as previous except: 20.v.1923 (1 ex. FSCA); same as previous except: 31.v.1923 (3 ex. FSCA); 10.vi.1923 (4 ex. FSCA); North Carolina: Jackson Co., Balsam, 6.v.1965, leg. W. Rosenberg (1 ex. FSCA); Macon Co., Watuaga Valley, 28.viii.1987, leg. F.N. Young, #3247A (1 ex. FSCA); Wake Co., Raleigh, Yates Pond, 12.ix.1970, leg. L.L. Lampert (8 ex. FSCA); North Dakota: Ransom Co., McLeod, 25.vii.1960, leg. J. Onsager (1 ex. MTEC); Ohio: Delaware Co., 4.x.1958, leg. E.I. Hazard (2 ex. FSCA) Franklin Co., Columbus, 20.v.1984, leg. M.A. Ivie (1 ex. MTEC); same as previous except: 1.viii.1985, leg. R.S. Miller (9 ex. MTEC); same as previous except: 7.viii.1985 (18 ex. MTEC); Columbus, Mere Pond, 23.viii.1985, leg. R.S. Miller (32 ex. MTEC); Lucas Co., nr West Toledo, Schwamberger Prarie, 10.vi.1984, leg. J.B. Stribling, UV light (1 ex. MTEC); Williams Co., Mudlake, 18.vii.1984, leg. J.A. Shuey (1 ex. MTEC); Muskingum Co., Zanesville, 2.v.1920, leg. A.E. Miller (3 ex. FSCA); Ross Co., Chillicothe, 1.viii.1992, leg. A.E. Miller (3 ex. FSCA); Oklahoma: Catoosa, 26.iv.1938, leg. E.K. Waering (1 ex. FSCA); same as previous except: 26.iv.1939 (1 ex. FSCA); same as previous except: 27.iii.1939 (1 ex. FSCA); Comanche Co., Ft. Still, 20.vi.1974, leg. T.E. Rogers (2 ex. FSCA); Latimer Co., 5 mi W Red Oak, v.1980, leg. K.H. Stephan (1 ex. FSCA); Latimer Co., 5 mi W Red Oak, ix.1980, leg. K.H. Stephan (10 ex. FSCA); Payne Co., Stillwater, 14.vii.1976 (1 ex. FSCA); nr Lake Carl Blackwell, 16.viii.1976 (1 ex. FSCA); South Carolina: Greenville Co., Greenville, 9.ix.1954, leg. H.L. Dozier (1 ex. FSCA); Newberry Co., 12.v.1968, leg. L.L. Lampert (1 ex. FSCA); Newberry Co., Jalapa, 24.iv.1973, leg. L.L. Lampert, light (1 ex. FSCA); Tennessee: Cuba, 25.v.1964, leg. K. Stephan (1 ex. FSCA); Obion Co., Reelfoot Lake S. P., 1/2 mi SE of Samburg, 4.vii.1983, leg. C.P. Withrow (2 ex. MTEC); Texas: Crosby Co., White River Lake, SW Area, 24.ix.1997, leg. Wappes & Huether (1 ex. FSCA); Runnels Co., Miles, 28.vi.1939, leg. H. Wilee Jr. (1 ex. FSCA); Waxahachie Co., Atlanta, 26.v.1964, leg. K. Stephan (1 ex. FSCA); Virginia: Rockingham Co., Craney Island, 7.x.1984, leg. C.L. Staines Jr. (1 ex. FSCA); West Virginia: Pocahontas Co., Cranberry Glades, 1213-1219 m, 27.vi.1967, leg. H.V. Weems, blacklight (1 ex. FSCA); Wisconsin: Dane Co., 18.v.1952, leg. D.H. Habeck (1 ex. FSCA).

No locality information: “Station.”, 8.v.1901, "Hatch Ex." (1 ex. MTEC); “E-2” (1 ex. FSCA).

Diagnosis.

Male (Fig. 8C-D): Size: 9.93-11.1 mm. Body form narrowly oval; elytral apices with sutural angle produced into a point, rarely with point reduced and elytra appearing completely rounded, elytral striae faint basally becoming more evident apically and laterally; profemora without sub-apicoventral tooth; protibia wedgeshaped, without distolateral margin produced; mesotarsal claws similar in size, with ventral margin straight; venter darkly colored, reddish brown to black often with a metallic shine present, epipleura similarly colored as thorax and abdomen; Aedeagus (Fig. 9A, B, D) median lobe in dorsal view acuminate in apical 1/5, apex narrowed and shortly rounded, in lateral view apex of median lobe barely curved dorsally, in ventral view sperm-groove parallel sided for near entirety of length, apex flatly rounded, parameres very weakly rounded laterally in apical 1/3.

Female (Fig. 8A-B): Size: 10-11.3 mm. Body form narrowly oval; elytral apices produced and rounded, with sutural angle produced into a point, apicolateral sinuation strong, elytral striae faint basally, becoming more evident apically and laterally; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, distolateral margin not expanded; venter darkly colored, reddish brown to black, often with metallic luster, epipleura similarly colored as thorax and abdomen.

Differential diagnosis.

Dineutus assimilis is unique among all North American species of Dineutus in the narrowly elongate oval body form, both sexes with the elytral apices more or less regularly rounded with the sutural angles produced, males with the profemora without a sub-apicoventral tooth, a wedge shaped protibia, mesotarsal claws that are similar in shape with their ventral margins straight, and the form of the aedeagus. The species most similar to Dineutus assimilis are Dineutus hornii and Dineutus nigrior , especially in the form of the females. Males of Dineutus assimilis can be separated from Dineutus hornii by the sutural angle of the elytra being regularly produced to a point, although rarely some individuals have the point reduced giving the elytra a regularly rounded look similar to those of Dineutus hornii . In such cases, specimens of Dineutus assimilis can be distinguished by the elytral epipleura being colored similarly to the adjacent thoracic and anterior abdominal ventrites (Fig. 8D), in contrast with Dineutus hornii in which the epipleura is different in color (much lighter) from the rest of the venter (Fig. 18D). The mesotarsal claws can also be used to separate males of Dineutus assimilis (Fig. 9C) from Dineutus hornii (Fig. 19C). In Dineutus assimilis the ventral margins of the claws are straight, whereas in Dineutus hornii they are very shallowly curved. Dineutus assimilis also have the ultimate antennomere angled, whereas in Dineutus hornii the antennal flagellum is short and thick, with the ultimate antennomere rounded. Males of Dineutus assimilis can be separated from Dineutus nigrior in their smaller size (9.9-11.3 mm), more narrow body form, and, most readily, by the mesotarsal claws which are similar in size with straight ventral margins, whereas in Dineutus nigrior the mesotarsal claws are distinctly asymmetrical with the anterior claw larger than the posterior and both having the ventral margins shallowly curved. The most reliable way to distinguish between Dineutus assimilis , Dineutus hornii and Dineutus nigrior is the aedeagus. The median lobe of the aedeagus of Dineutus assimilis (Fig. 9A) is acuminate in the apical 1/5. The aedeagi of both Dineutus hornii and Dineutus nigrior are more elongate and parallel sided with the median lobe apically narrowed but not acuminate.

Females of Dineutus assimilis are more difficult to differentiate from Dineutus hornii and Dineutus nigrior . Females of Dineutus assimilis differ from those of Dineutus hornii in the epipleura color being similar to the adjacent thoracic anterior abdominal ventrites, whereas in Dineutus hornii the epipleura are lighter in color than the surfaces of the thorax and abdomen (Fig. 18B). The elytral apices of the females of Dineutus assimilis are more similar to those of Dineutus nigrior . In general Dineutus assimilis is smaller (10-11.3 mm) than Dineutus nigrior , and also more narrowed in body form. The most reliable way to separate Dineutus assimilis from Dineutus nigrior is the distal lateral margin of the protibiae. In Dineutus assimilis the distal lateral margin is not produced laterally (Fig. 8B), but continuously weakly curved, whereas in Dineutus nigrior the margin is laterally weakly expanded (Fig. 31B).

Distribution

(Fig. 52A). Southern Canada from British Columbia to Nova Scotia ( Majka 2008; Roughley 1991; Webster and DeMerchant 2012), and east of the Rocky Mountains in the U.S.A. as far south as Texas and Northern Florida ( Epler 2010; Ferkinhoff and Gunderson 1983; Folkerts 1978; Gordon and Post 1965; Hilsenhoff 1990; Malcolm 1971; Régimbart 1907; Roberts 1895; Sanderson 1982; Whiteman and Sites 2003; Wood 1962).

Habitat.

This is most widespread and commonly encountered species of Dineutus in North America, occupying both lotic and lentic habitats ( Woods 1962; Hilsenhoff 1990; Whiteman and Sites 2003). The first author has collected this species in a secondary growth deciduous forest, Baldwin Woods, near Baldwin, Kansas, in a large forest pond with a muddy bottom, with plenty of leaf detritus and several fallen emergent trees. Here Dineutus assimilis was found in large numbers near the shore, with others often exploring deeper regions of the pond. In New Brunswick, Canada, Dineutus assimilis was collected in similar habitats, the margins of ponds with emergent vegetation within forests composed of red oak and red maple ( Webster and DeMerchant 2012). Webster and DeMerchant (2012) also found Dineutus assimilis in black spruce and tamarack bogs. This species has also been collected in other lentic situations from the Prairie Region of Missouri, where Whiteman and Sites (2003) found specimens associated with the following plant taxa: Brasneia , Ceratophyllum , Juncus , Lespedeza , Ludwigia , Polygonum , Potamogeton , Sagittaria , Typha , Cyperaceae , and Poaceae . This species also comes to ultraviolet light ( Webster and DeMerchant 2012).

Discussion.

Dineutus assimilis is the most commonly encountered species of Dineutus in North America, and has one of the largest ranges of any North American species (Fig. 52A), often erroneously listed under the name Dineutus americanus , even recently (e.g. Ciegler et al. 2003). As early as 1927, Ochs (1927b) had the types of Dineutus americanus examined by an associate in London, and determined unambiguously that Dineutus americanus is the Caribbean species, with Dineutus assimilis found in mainland North America. We have again confirmed, after examination of the syntype of Dineutus americanus , that Dineutus assimilis is not Dineutus americanus of Linnaeus. It is likely all records of Dineutus americanus from areas not in the Caribbean or the Florida Keys actually represent Dineutus assimilis . An example of references clearly referring to Dineutus assimilis is Zuellig et al. (2002), who recorded " Dineutus americanus " from Wyoming. Hatch’s (1927) key to the larvae of " Dineutus americanus " most likely refers to Dineutus assimilis as well.

The juvenile stages have been formally described and illustrated by Wilson (1923) and sparse life history information is available in Smith (1926) and Istock (1966; 1967).