Dineutus hornii Roberts, 1895

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 : 43-47

Dineutus hornii Roberts, 1895 Figures 18, 19, 52

Dineutes hornii Roberts 1895: 282, Dineutes horni : Régimbart 1907: 147, Dineutus (Cyclinus) horni : Ochs 1926a: 136, Dineutus (Cyclous) hornii : Hatch 1927: 28, Dineutes horni : Leonard 1928: 263, Dineutus (Cyclinus) hornii : Hatch 1930: 20, Dineutus hornii : Ferkinhoff and Gunderson 1983: 16.

Type localty.

New York.

Specimens examined.

45

Type material examined.

Syntype (♂ pinned, aedeagus extruded) "N.Y./Acc. 4858/Lectotype/ hornii ♂type # 4 C.H.R./LECTOTYPE Dineutus horni Desig: R.P. Withington III 1998/ Dineutus hornii Roberts 1895 Det. L. Cook 2005" AMNH catalog no. 497.

Material examined.

U.S.A.: Iowa: Boone Co., Ledges State Park, 2.v.1955, leg. M.D. Hoffman (2 ex. FSCA); Indiana: Brown Co., nr. Crooked Creek, 1.x.1977, leg. F.N. Young (1 ex. FSCA); Posey Co., Hovey Lake, 17.viii.1965, leg. C.E. White, Blacklight trap (1 ex. FSCA); Massachusetts: Middlesex Co., Hopkinton, 9.v.1915 (1 ex. FSCA); Michigan: Berrien Co., Harbert Dunes, 17.vii.1956, leg. G.H. Nelson, under washup (1 ex. FSCA); Cheboygan Co., 29.vii.1928, leg. F.G. Batcher, (1 ex. KSEM); same as previous except: 25.vii1931, leg. H.B. Hungerford (1 ex. KSEM); Cheboygan Co., Douglas Lake, 29.vii.1927, leg. H.B. Hungerford (1 ex. KSEM); Cheboygan Co., Douglas Lake, Bessey Cr., 30.vi.1925, leg. H.B. Hungerford (1 ex. KSEM); New Hampshire: Carroll Co., “Summer” 1934, leg. N.H. Preble (4 ex. KSEM); New York: Broome Co., nr. Binghamton, 10.vii.1997, leg. K.B. Miller (8 ex. MSBA); Schuyler Co., Texas Hollow State Wildlife Area, 1.ix.1999, leg. K.B. Miller (2 ex. MSBA); Tompkins Co., Ringwood, 42°26'33"N, 76°21'47"W, 20.v.2000, leg. K.B. Miller (7 ex. MSBA); Saint Lawrence Co., Black Lake, 27.vii.1941, leg. E.J. Gerberg (1 ex. FSCA); Westchester Co., White Plains, 14.v.1922, leg. E.H.P. Squire (1 ex. FSCA); same as previous except: 30.v.1923 (1 ex. FSCA);

Putnam Co., Carmel, 2.viii.1923, leg. E.H.P. Squire (2 ex. FSCA); Pennsylvania: Sussex Co., Peck’s Pond, 41°16'55.4"N, 75°15'18"W, 414 m, 29.v.2007, leg. P.A. Lenhart, swimming in pond (2 ex. MSBA); South Carolina: Aiken Co., Jackson, 4 mi NW at hwy 125 bridge, Holley Creek, 25.iii.1980, leg. D. Huggins, S. Hamilton, SEMC 1054964 (1 ex. KSEM); Wisconsin: Richland Co., lower WI River, State Wildlife Area, 2 mi W of Lone Rock, 4.x.1997, leg. A. Ramsdale, on surface of lentic pond, near margin, day (6 ex. MTEC).

Diagnosis.

Male (Fig. 18C-D): Size: 9.9-10.9 mm. Body form narrowly oval; antennal flagellum short and thick, ultimate segment broad and round; elytral apices rounded, rarely angled toward suture, elytral striae faintly; profemora without sub-apicoventral tooth; protibiae wedge-shaped, with distolateral margin straight; mesotarsal claws (Fig. 19C) similar in size, venter darkly colored reddish brown to black, except epipleura lighter in color, yellow to orange; Aedeagus (Fig. 19A, B, D) median lobe in dorsal view mostly parallel sided, evenly narrowed in apical 1/3, apex strongly narrowed, flatly rounded, in lateral view apex of median lobe weakly curved dorsally; parameres in dorsal view laterally expanded in apical 1/4, nearly evenly rounded apically, in ventral view sperm grove narrow and parallel sided for most its length.

Female (Fig. 18A-B): Size: 10.3-11.3 mm. Body form narrowly oval; antennal flagellum short and thick, ultimate segment broad and round; elytral apices produced, angled towards sutural production, sutural angle produced into a point, apicolateral sinuation present, elytral striae faint basally and laterally, mainly evident apicomedially, becoming more evident apically and laterally; profemora without sub-apicoventral tooth; protibiae laterally weakly curved, distolateral margin weakly expanded; venter darkly colored, reddish brown to black, except epipleura lighter in color, yellow to orange.

Differential diagnosis.

Dineutus hornii can be distinguished from all other North American species of Dineutus in having the epipleura light yellow to orange, while still having a darkly colored venter (as opposed to similarly lightly colored as in Dineutus discolor ) (Fig. 18B, D), and the males by the form of the aedeagus (Fig. 19A). The species most similar to Dineutus hornii are Dineutus assimilis and Dineutus nigrior especially the female forms. But both sexes differ from the following two species in having the epipleura (Fig. 19B, D) lightly colored yellow to orange relative to their darker venters, as well as having antennal flagella that are short and thick with the ultimate segment appearing broad and round. In both Dineutus assimilis and Dineutus nigrior the epipleura is similarly darkly colored like the rest of the venter, and in Dineutus assimilis often accompanied with a metallic sheen. The ultimate segment of the antennal flagellum in both species differs in being angled as opposed to rounded as in Dineutus hornii .

Males of Dineutus hornii can be readily distinguished from both Dineutus assimilis and Dineutus nigrior in having the elytral apices rounded (rarely angled towards the suture) and without the sutural angle produced to a point (Fig. 18C). The aedeagus (Fig. 19A) of Dineutus hornii is more similar to Dineutus nigrior (Fig. 32A), but can distinguished by the median lobe in dorsal view being more parallel sided, being evenly narrowed in the apical 1/3 (as opposed to apical 1/4), and having the apex of the median lobe flatly rounded at the tip. The median lobe also differs from Dineutus nigrior in having the apex weakly curved dorsally in lateral view (Fig. 19D) as opposed to strongly curved in Dineutus nigrior (Fig. 32D). The pararmeres of Dineutus hornii differ from those of Dineutus nigrior in being expanded laterally in the apical 1/4, and evenly rounded apically, and in lateral view being obtusely angled after the basal 1/3 as opposed to strongly angled.

Females of Dineutus hornii can be somewhat fairly easily distinguished from those of Dineutus assimilis and Dineutus nigrior in that the apices of the elytra are angled towards the suture (Fig. 18A) as opposed to being rounded towards the produced sutural angle. This character combined with the epipleural color and the antennal flagellum shape should readily distinguish females of Dineutus hornii from both Dineutus assimilis and Dineutus nigrior .

Distribution

(Fig. 52B). Extreme southeastern Canada from Saskatchewan to Nova Scotia ( Majka 2008; Majka and Kenner 2009; Roughley 1991) and the eastern half of the United States as far south as Texas and northern Florida ( Epler 2010; Ferkinhoff and Gunderson 1983; Folkerts 1978; Hilsenhoff 1990; Malcolm 1971; Roberts 1895; Sanderson 1982; Whiteman and Sites 2003; Wood 1962).

Habitat.

This species is primarily lentic and occasionally found in streams ( Hilsenhoff 1990; Whiteman and Sites 2003). In Canada Dineutus hornii inhabits boggy and semi-boggy lakes ( Morrissette 1979). In the Missouri Prairie Region, Whiteman and Sites (2003) record this species in ponds with Brasneia .

Discussion.

The spelling of the specific epithet hornii is in some places spelled horni, but the discrepancy in spelling was clarified by Majka (2008), finding " horni " to be an incorrect subsequent spelling of hornii. The unambiguously correct spelling is Dineutus hornii (Majka, 2008).

Dineutus hornii forms rafts during the daytime consisting of hundreds to thousands of individuals, which may be composed of multiple species ( Heinrich and Vogt 1980). At night some individuals disperse to forage, returning to larger rafts of beetles just before dawn, while others do not leave the larger rafts formed during the day ( Heinrich and Vogt 1980), unlike the behavior observed by Fitzgerald (1987) for Dineutus nigrior where the diurnal rafts of this species appeared to totally disperse by night. Heinrich and Vogt (1980) suggest that Dineutus hornii is nocturnal as foraging behavior occurs at night, with the diurnal period spent quiescently in rafts. Brief life history is available in Istock (1966; 1967).

The larva of Dineutus hornii was included in a key to gyrinid larvae by Hatch (1927) and the structure of the egg has been describe by Baker and Wai (1987).