Dineutus truncatus Sharp, 1873

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 : 83-87

Dineutus truncatus Sharp, 1873 Figures 30, 47, 48, 54

Dineutes truncatus Sharp 1873: 54, Dineutus truncatus : Ochs 1924: 1, Dineutus (Dineutus) truncatus : Ochs 1926a: 138, Dineutus truncatus : Blackwelder 1944: 81, Dineutus (Dineutus) truncatus : Ochs 1949: 288, Dineutus (Cyclinus) truncatus : Brinck 1955: 106, Dineutus truncatus : Arce-Pérez and Roughley 1999: 84.

Type locality.

Chontales, Nicaragua, BMNH

Specimens examined.

34

Type material.

Not examined.

Material examined.

COSTA RICA: Alajuela: Zapote Upala, nr. Bijaqua, 20.x.1973, leg. F. Cordera EMEC 204671 (1 ex. EMEC); same as previous except: 10.ix.1973, leg. R. Ortiz, EMEC 204908 (1 ex. EMEC); Guanacaste: Rincon de la Vieja N.P., Quebrada Cataracta, 15.vi.2003, leg. W.D. Shepard, EMEC 204646-204667 (22 ex. EMEC); Puntarenas: Las Cruces Bio. Station, water tank, 1158 m, 19.vi.2003, leg. A.E.Z. Short, (2 ex. KSEM); Monte Verde, Rio Guacimal, 1420 m, 15.v.1989, leg. J. Ashe, R. Leschen, R. Brooks, Snow Entomol. Mus. Costa Rica Exped. #198 (1 ex. KSEM); 6 km S Sta. Elena, 6-7.vi.1983, leg. J.E. Wappes (1 ex. FSCA). PANAMA: Ngäbe-Buglé: nr. Soloy, 8°36.554'N, 82°07.814'W, 7.vi.2009, leg. Nearns, Lord, small stream (6 ex. MSBA).

Diagnosis.

Male (Fig. 47C-D): Size: 13.5-15.4 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, fine serration present apically, apicolateral margin without sinuation, elytral striae primarily indistinct, dense microreticulation covering entirety of elytra and pronotum, producing a polished metal feel, elytra often with violet iridescence; ulimate protarsus (Fig. 30C) ca. 2 × as long as wide; protibiae club-shaped; profemora with small acute sub-apicoventral tooth; mesotarsal claws (Fig. 48C) without ventral margin expanded into weak denticle; venter darkly colored, usually black to dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen; Aedeagus (Fig. 48A, B, D) median lobe in dorsal view nearly evenly attenuated basally to apically, more strongly narrowed in apical 1/3, apex very shortly rounded, not acuminate, in lateral view median lobe ventrally weakly sinuate in apical 1/3, noticeably dorsally curved, ventrally median lobe with parallel sided sperm-groove, parameres as wide as base of median lobe apically, weakly laterally expanded in apical 1/3.

Female (Fig. 47A-B): Size: 13.3-15.1 mm. Body form regularly oval; elytral apices truncate, lateral corner of truncation roundly angled, fine serration present apically, apicolateral margin without sinuation, elytral striae primarily indistinct, visible upon close examination, dense microreticulation covering entirety of elytra and pronotum, producing a polished metal feel, elytra often with violet iridescence; ulimate protarsus ca. 2 × as long as wide; protibiae club-shaped; profemora without sub-apicoventral tooth; venter darkly colored, usually black to dark reddish brown, mesothoracic and metathoracic legs usually lighter in coloration, as well as apex of abdomen.

Differential diagnosis.

Dineutus truncatus is unique among all other New World Dineutus in having the elytral apices truncate, with fine serration present apically, males with the ultimate protarsomeres (Fig. 30C) ca. 2 × as long as wide, profemora with a small sub-apicoventral tooth present, mesotarsal claws with ventral margins not expanded into a weak denticle (Fig. 48C), and in the form of the male aedeagus (Fig. 48A). The species most similar to Dineutus truncatus is Dineutus mexicanus (originally described as a subspecies of Dineutus truncatus by Ochs [1925a]). Both species have their elytral apices truncate, however only Dineutus truncatus has the elytral apices with fine serration present, those of Dineutus mexicanus have the serration much more blunt and thick and/or reduced, in some specimens down to only irregularities of the elytral apices. There is a general difference between the species in the dorsoventral convexity of the body form in lateral view. In general, Dineutus truncatus tends to be noticeably more humped in the scutellar region with the posterior length of the elytra more dorsoventral depressed, while in Dineutus mexicanus the posterior length of the elytra is less dorsoventrally depressed, giving Dineutus mexicanus a generally less dorsoventrally convex lateral profile, without as much of a pronounced hump in the scutellar region.

Males of Dineutus truncatus can further be separated from males of Dineutus mexicanus by several characters. In Dineutus truncatus the elytral striae, while present, are nearly indistinct and are weakly impressed, while in Dineutus mexicanus the striae are evident just posterior to the middle of the elytra, disappearing laterally and before the elytral apices. The protarsi (Fig. 30) have several characters separating Dineutus truncatus from Dineutus mexicanus . The size of the ultimate protarsomere in Dineutus truncatus (Fig. 30C) is ca. 2 × as long as wide, while in Dineutus mexicanus (Fig. 30A) the ulimate protarsomere is less than 2 × as long as wide. The shape of the lateral margins of the protarsal tarsomeres 2-5 also differs among the species. In Dineutus truncatus , in anterior view, the tarsomeres are laterally flatly rounded (Fig. 30C), this differs strongly from a specimen of uncertain species assignment from Oaxaca (see specimens of uncertain placement below) in which the lateral margins of the protarsi in anterior view are roundly angled (Fig. 30B), but are similar to those of Dineutus mexicanus (Fig. 30A). The mesotarsal claws can also assist in separating the males of Dineutus truncatus (Fig. 48C) from Dineutus mexicanus (Fig. 29C), in that the ventral-margins lack an expansion forming a weak denticle. By far the most reliable way to separate the males of these species is by the form of the aedeagus. In Dineutus truncatus (Fig. 48A) the median lobe of the aedeagus is nearly evenly tapered basally to apically, with the apex narrowly rounded and appearing highly pointed, as opposed to the being acuminate as in Dineutus mexicanus (Fig. 29A).

Females of the species are primarily separated by the general differences listed between the species for elytral differences and body form differences. The size of the ultimate protarsomere in females shows similar ratios to the males being ca. 2 × as long as wide in Dineutus truncatus , while in Dineutus mexicanus the ulimate protarsomere is less than 2 × as long as wide.

Distribution

(Fig. 54D). Known only from Central America from Nicaragua to western Panama ( Ochs 1949; Sharp 1882).

Habitat.

Lotic and lentic ( Ochs 1949). The authors have collected this species from a medium sized stream with clear water, running through a small agrarian valley in Chiriquí, Panama. In the stream Dineutus truncatus was found in areas outside of the rapids where the water slowed and pooled, such as the stream margins or behind large rocks in the stream.

Discussion.

This species has the most southern range of any New World Dineutus being found only in Central America, as far south as Panama. It is unclear however, the true extent of the range of Dineutus truncatus . In Panama, all specimens observed in this study were from the western half of the country near Soloy and Chiriquí, with most references in the literature for the distribution of Dineutus truncatus in Panama only mentioning the latter locality ( Sharp 1882; Ochs 1949). The north and western limits of this species’ range is even less clear. The type locality is Chontales, Nicaragua, and the species is readily found in Costa Rica, but literature references also suggest the limits may be as far northwest as Guatemala and Mexico ( Sharp 1873, 1882; Ochs 1949). It is likely as previously suggest by Ochs (1949) that these data refer to Dineutus mexicanus . Dineutus mexicanus is superficially very similar to Dineutus truncatus in habitus and specimens determined to be Dineutus mexicanus in this study included a female specimen from Guatemala, and others from as far southeast as El Salvador. As is often becoming the case in Dineutus , some very similar species have overlapping ranges with one having a very limited range of endemism relative to a another more widely ranging species. Dineutus truncatus follows this pattern in relation to Dineutus mexicanus , seemingly only definitely being found in Nicaragua, Costa Rica, and western Panama. As is the case with other species with narrow ranges Dineutus truncatus specimens were relatively few in number, and it is not well represented in many museums.

The authors have collected this species from mountainous Chiriquí, in western Panama, the place where numerous historical references record specimens ( Ochs 1949; Sharp 1873). The species is quite common through Costa Rica, which is dominated by central mountain ranges, and its type locality is Western Nicaragua, the mountain ous region of the country. These records appear to suggest that Dineutus truncatus may be restricted to mountainous regions, and may be a mountain endemic, similar to the situation possibly seen in Dineutus mexicanus . It may be that the most southeastern extent of Dineutus mexicanus ' range is the Cordillera de Talamanca in Panama, and the northwestern most portion of its range may reflect Nicaraguan mountain ranges.

In Costa Rica where Dineutus truncatus is very common it has been given the common name of “mamatetas” ( Ochs 1949; Hogue 1993). The literal translation from Spanish appears to mean nipple sucker or nipple suckling. Ochs (1949) translated this name to “dug-sucker” which the second meaning for dug is nipple, in agreement with the translation. The reason for this common name does not appear to be known. Ochs (1949) says that Nevermann believed it to come from superstitious ideas, but does not elaborate, nor does Ochs (1949) provide a citation for Nevermann’s interpretation, for further investigation. An interesting connection to the name mamatetas and the literal translation of nipple sucker, is the practice of some young girls in East Africa to use gyrinids to stimulate breast growth ( Kutalek and Kassa 2005). Young girls allow gyrinids to bite their nipples in hopes of stimulating the breasts to grow larger, and interestingly, among the gyrinids in use are common African species of Dineutus ( Kutalek and Kassa 2005). It is unclear, if there is any similar practice present in Costa Rica, thus resulting in the common name referring to breast suckling.