Dineutus nigrior 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 : 57-60

Dineutus nigrior Roberts, 1895 Figures 31, 32, 52

Dineutes nigrior Roberts 1895: 280, Dineutus (Cyclinus) nigrior : Hatch 1926 a: 311, Dineutus (Cyclous) nigrior : Hatch 1927: 28, Dineutus (Cyclinus) nigrior : Hatch 1930: 20. Dineutes nigrior : Brimley 1938: 132, Dineutus (Cyclinus) nigrior : Guignot 1950: 126, Dineutus nigrior : Ferkinhoff and Gunderson 1983: 19.

Type locality.

USA, Vermont.

Specimens examined.

34

Type material examined.

Syntype (♂ pinned, aedeagus extruded) "Bengtn. Co., Vt./Acc.4858/ LECTOTYPE/ nigrior ♂ type # 1 C.H.R./LECTOTYPE Dineutus nigrior Desig: R.P. Withington III 1998/ Dineutus nigrior Roberts 1895 Det: L. Cook 2005" AMNH type catalogue no. 498.

Material examined.

U.S.A.: Delaware: Sussex Co., Milsboro, 13.v.1973, leg. T.E. Rogers (1 ex. FSCA); Florida: Alachua Co., Gainesville, 27.vi.1961, leg. R.F. Bussey (1 ex. FSCA); Liberty Co., Torreya State Park, 25.v.1981, leg. J.R. Watts, at U.V. (1 ex. FSCA); Indiana: Crawford Co., Grantsburg, 18.vii.1965, leg. D. Eckert, Blacklight trap (1 ex. FSCA); Maryland: Prince George’s Co., College Park, 16.vi.1948, leg. B.K. Detler, in pond (1 ex. FSCA); Prince George’s CO., Blue Pond, 29.ix.1949, leg. H.L. Dozier, (1 ex. FSCA); Massachusetts: Suffolk Co, Forest Hills, 18.iv.1919 (1 ex. FSCA); Michigan: Allegan Co., State Game Area, 17.vii.1986, leg. J.A. Shuey (1 ex. MTEC); Cheboygan Co., Douglas Lake, 30.vii.1927, leg. H.B. Hungerford (1 ex. KSEM); same as previous except: "Mud L", 31.vii.1923 (1 ex. KSEM); Washtenaw Co., "118 8h", 24.iv.1921, leg. M.H. Hatch (1 ex. FSCA); Minnesota: Clearwater Co., Elk Springs, Itasca State Park, 12.viii.1965, leg. J.S. Nordin, attracted to U.V. (2 ex. FSCA); same as previous except: 7.vii.1965 (1 ex. FSCA); Morner Co., nr. Grand Meadow, roadside park, 18.viii.1965, leg. R.H. Arnett, in dammed pond (2 ex. FSCA); Missouri: Wayne Co., 3.2 mi WSW of Patterson Co. Rd. 332, deciduous Ozark forest and old field flora, 4.vii.1988, leg. H.M. Webber, at U.V. light (1 ex. FSCA); New Jersey: Cumberland Co., "Dividing Ck. Hansey Creek Rd.", edge of salt marshes, 30.ix.1989, leg. D. Schloeitzer, at UV light (1 ex. FSCA); New York: Schuyler Co., Texas Hollow State Wildlife Area, 1.ix.1999, leg. K.B. Miller (1 ex. MSBA); Westchester Co., White Plains, 5.ix.1922, leg. E.H.P. Squire (1 ex. FSCA); same as previous except: 3.viii.1923 (2 ex. FSCA); same as previous except: 19.v.1923 (1 ex. FSCA); same as previous except: 30.v.1923 (1 ex. FSCA); same as previous except: 10.iii.1923 (1 ex. FSCA); same as previous except: 18.x.1924 (2 ex. FSCA); same as previous except: 12.iv.1925 (1 ex. FSCA); same as previous except: 19.v.1925 (1 ex. FSCA); Westchester Co., Montrose, 4.vii.1932, leg. C.L. Ragot (1 ex. FSCA); Pennsylvania: Sullivan Co., Picketts Glen St. Pk., 5.vii.1960, leg. G.W. Byers (2 ex. KSEM); Virginia: Giles Co., Mt. Lake Biol. Stat., 30.vi.1968, leg. H. Greenbaum (1 ex. FSCA); Wisconsin: Douglas Co., State Hunting Grounds, “T44N.R12W.Sec.11”, 23.vi.1999, leg. A Ramsdale, black light in barrens (1 ex. MTEC).

Diagnosis.

Male (Fig. 31C-D): Size: 11.1-11.7 mm. Body form narrowly oval; elytral apices with sutural angle produced into a point, elytral striae faint basally becoming more evident apically and laterally; profemora without a sub-apicoventral tooth; protibiae wedge-shaped, with distolateral margin produced; mesotarsal claws markedly asymmetrical (Fig. 32C), anterior mesotarsal claw larger than posterior claw, venter darkly colored, reddish brown to black with mesothoracic and metathoracic legs lighter in color; Aedeagus (Fig. 32A, B, D) median lobe in dorsal view narrowed in api cal 1/4, shortly rounded apically, in lateral view apex of median lobe strongly curved dorsally, parameres strongly curved in lateral view after basal 1/3.

Female (Fig. 31A-B): Size: 11.6-11.7 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 weakly expanded; venter darkly colored, reddish brown to black venter darkly colored, reddish brown to black with mesothoracic and metathoracic legs lighter in color.

Differential diagnosis.

This species is unique among all other species of North American Dineutus in the extremely large size and assymetrical nature of the male mesotarsal claws (Fig. 32C) and the form of male aedeagus (Fig. 32A, B, D). The species most similar to Dineutus nigrior are Dineutus assimilis and Dineutus hornii , of the two the former most closely resembles Dineutus nigrior especially the female members of the species. Females of all three species very closely resemble one another and require careful consideration for identification. Males of the species can be fairly readily distinguished externally, and aedeagal dissections can indisputably separate males of the species.

In general males of Dineutus nigrior can be distinguished from members of Dineutus assimilis and Dineutus hornii by size. Dineutus nigrior males are larger (Size: 11.1-11.7 mm) than males of both Dineutus assimilis and Dineutus hornii . Dineutus nigrior males differ from males of Dineutus hornii in having the sutural angle of the elytral apices produced into a point, and the venter of Dineutus nigrior is much more darkly colored than that of Dineutus hornii , with the epipleura being similarly colored as the thoracic ventrites. Males of Dineutus nigrior can be distinguished from both Dineutus assimilis and Dineutus hornii in having the mesotarsal claws markedly asymmetrical (Fig. 32C) with the anterior tarsal claw being larger than the posterior claw, while in both Dineutus assimilis (Fig. 9C) and in Dineutus hornii (Fig. 19C) the mesotarsal claws are similar in size. The distolateral margin of the protibiae in Dineutus nigrior is produced while in Dineutus assimilis and Dineutus hornii the margin is straight or nearly so. The aedeagus of Dineutus nigrior (Fig. 32A) is most similar to Dineutus hornii (Fig. 19A) but can be distinguished from Dineutus hornii in having the apex of the median lobe strongly curved dorsally in lateral view (Fig. 32D).

The females of Dineutus nigrior are also generally larger (Size: 11.6-11.7 mm) than those of Dineutus assimilis and Dineutus hornii , but unlike the case in the males, females of each of these three species have the sutural angles of the elytra produced into a point. However, the shape of the apices differs between them. In females of Dineutus nigrior the apices of the elytra are regularly rounded, and this situation is most different from Dineutus hornii where the apices are generally angled towards the sutural production. Dineutus nigrior females can be separated from both Dineutus assimilis and from Dineutus hornii in having the distolateral protibial margin produced, similar to the condition in males, but more weakly expanded.

Distribution

(Fig. 52C). Extreme southeastern Canada from Manitoba to Nova Scotia ( Majka 2008; Majka and Kenner 2009; Roughley 1991) and most of the eastern half of the United States as far south as northern Florida ( Epler 2010; Folkerts 1978; Gordon and Post 1965; Hilsenhoff 1990; Malcolm 1971; Régimbart 1907; Roberts 1895; Sanderson 1982; Whiteman and Sites 2003; Wood 1962).

Habitat.

Primarily lentic species, found only infrequently in streams ( Roberts 1895; Hilsenhoff 1990). In Canada, Dineutus nigrior prefers semi-boggy lakes ( Morrissette 1979). In the Missouri Prairie Region, Whiteman and Sites (2003) found this species associated with the plant taxa Brasneia and Lespedeza .

Discussion.

Fitzgerald (1987) described the social system of Dineutus nigrior in detail and Fairn et al. (2008) studied the effects of parasitism by larval water mites of the genus Eylais Latreille, 1796 on adults of Dineutus nigrior . Evidence for sexual selection within this species has also been investigated ( Fairn et al. 2007a; Fairn et al. 2007b). Brief life history information is available in Istock (1966; 1967).

Key to the larvae of Dineutus nigrior provided by Hatch (1927).