Dineutus robertsi Leng, 1911

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 : 62-66

Dineutus robertsi Leng, 1911 Figures 35, 36, 53

Dineutes robertsi Leng 1911: 11, Dineutus (Dineutus) robertsi : Ochs 1926: 138, Dineutus robertsi : Leech 1938: 61, Dineutus (Protodineutus) robertsi : Guignot 1950: 126, Dineutus (Cyclinus) robertsi : Brinck 1955: 106, Dineutus robertsi : Sanderson 1982: 10.30.

Type locality.

U.S.A., Georgia: "West Branch War Woman Creek, Rabun Co., Ga., in the mountains, at an elevation of about 2,000 feet.".

Specimens examined.

59

Type material examined.

Not examined, but specimens collected from the type locality.

Material examined.

U.S.A.: Georgia: Clayton Co., Warwoman Wldf Mgmt A, Tuckaluge Cr., 34.90155°N 83.30015°W, 533 m, 11.vii.2012, leg. K.B. Miller, KBM11071201 (31 ex. MSBA); Warwoman Cr., 34.89843°N 83.27512°W, 11.vii.2012, leg. K.B. Miller, KBM11071202 (8 ex. MSBA); Cleveland Co., Chattahoochee R., 34.72111°N, 83.74807°W, 12.vii.2012, leg. K.B. Miller, KBM12071202 (11 ex. MSBA); South Carolina: Moutain Rest Co., Sumter Ntl. For., 34.85292°N 83.14336°W, 12.vii.2012, leg. K.B. Miller, KBM11071203 (9 ex. MSBA).

Diagnosis.

Male (Fig. 35C-D): Size: 12.1-15.5 mm. Body form elongate broadly oval; antennal flagellum narrow and parallel sided, ultimate segment elongate and pointed apically; elytral apices regularly rounded, serration absent, elytra entirely bronzy, elytral striae faint but fairly distinct, 8th elytral stria with large shallow punctures present; profemora without sub-apicoventral tooth; protibiae club-shaped; anterior mesotarsal claw (Fig. 36C) with strong denticle; venter lightly colored yellow to light orange in coloration; Aedeagus (Fig. 36A, B, D) medial lobe in dorsal view flatly rounded apically, in ventral view sperm-groove triangular, narrowed posteriorly and anteriorly, in lateral view median lobe thick and flat, parameres strongly arced in apical 1/3.

Female (Fig. 35A-B): Size: 13.6-15.1 mm. Body form elongate broadly oval; antennal club narrow and parallel sided, ultimate segment elongate and pointed apically; elytral apices regularly rounded, serration absent, elytra entirely bronzy, elytral striae faint but fairly distinct, 8th elytral stria with punctures present; profemora without sub-apicoventral tooth; protibiae club-shaped; venter pale yellow in coloration.

Differential diagnosis.

This species is easily distinguished from all other North American species of Dineutus by its large size, profemora lacking a sub-apicoventral tooth, entirely bronzy elytra, and broadly oval body shape with a pale yellow venter. Other North American species with pale venters are much more attenuated in body shape (e.g. Dineutus discolor , Dineutus longimanus ).

The species most similar to Dineutus robertsi is Dineutus ciliatus . Dineutus robertsi differs from Dineutus ciliatus in having the antennal club narrow and parallel sided, with the ultimate segment elongate and pointed apically, as opposed to having the flagellum being thicker and rounder with the ultimate segment rounded. Dineutus robertsi also has the 8th elytral stria with punctures evident laterally as opposed to having them absent or indistinct as in Dineutus ciliatus . The males of Dineutus robertsi can further be distinguished from Dineutus ciliatus in having the anterior mesotarsal claw (Fig. 36C) with a strong denticle. The aedeagus of Dineutus robertsi (Fig. 36A) has the median lobe in dorsal view flatly rounded apically with the apex lacking an apicomedial papilla, as compared to Dineutus ciliatus (Fig. 13A) in which an apicomedial papilla is present. In ventral view (Fig. 36B), the sperm-groove of the median lob is triangular, narrowed posteriorly and anteriorly, as opposed to that of Dineutus ciliatus (13B) which is broader and more parallel sided. In lateral view the median lobe of Dineutus robertsi (Fig. 36D) is thick and flat, not dorsally curved as is the case in Dineutus ciliatus (Fig. 13D). The parameres also differ in being strongly arced in apical 1/3, those of Dineutus ciliatus are weakly arced.

Distribution

(Fig. 53B). Known from the Appalachian mountains of northeastern Georgia, and southwestern North and South Carolina in the United States ( Leng 1911; Sanderson 1982; Wood 1962).

Habitat.

Lotic species, frequenting mountainous streams with rocky bottoms. The second author collected many specimens from moderately high gradient, rocky streams in higher elevation mountainous regions in the southern Appalachians. Specimens were common in pools and margins of the streams. They were not found at lower elevations or on larger rivers where they were replaced by Dineutus discolor and Dineutus ciliatus .

Discussion.

Dineutus robertsi is highly endemic to the Appalachians of northeastern Georgia and southwestertn North and South Carolina (Fig. 53B). For this reason Dineutus robertsi has been infrequently collected and is poorly represented in collections. Once in the range of this species however, it can be regularly collected on mountain streams, and in large numbers. The full extent of the range of Dineutus robertsi is still in question. Further sampling of the Appalachians would be greatly beneficial for determining the extent of the range of this highly endemic species.