Balgus schnusei
Creators: name: Barbosa, Felipe Francisco
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Eucnemidae
Balgus
Balgus schnusei

description: Balgus schnusei (Heller, 1914)
(Figure 8)
Pterotarsus schnusei Heller, 1914: 73, 74 (original description).
Balgus Schnusei Fleutiaux, 1920: 98 (new combination); Schenkling, 1928: 7 (catalogue).
Balgus schnusei Blackwelder, 1944: 275 (catalogue, correction of the specific epithet under the article 32.5.2.5 of ICZN, Schnusei to schnusei); Costa, 1984: 397, 398 (new distribution register, bioluminescence note); Chassain & Touroult, 2010: 21 (catalogue); Chassain & Touroult, 2013: 78, 79, 81 (redescription).
Balgus schnusei cayennensis Chassain, 2003: 81 –84 (original description); Chassain & Touroult, 2010: 21 (catalogue); Chassain & Touroult, 2013: 77, 78, 79, 81 (redescription, aedeagus described) syn. nov.
Diagnosis. Subcylindrical body (Figures 8A, B, C, F); finely and sparsely punctated; posterior half of pronotum with rounded lateral posterior tubercle (tubercle bioluminescent); dorsal and ventral regions covered with very short yellow or golden setae; elytra provided with several oblong tubercles, more or less longitudinally aligned.
Redescription. Subcylindrical body, attenuate narrowing on the posterior fourth. Elytra about three times as long as pronotum. Finely and sparsely punctated. Dorsal and ventral region covered with very short yellow or golden setae.
Color: Antennae light brown; antennal rami brown, yellow apically. Pronotum and elytra light brown. Some regions between darker tubercles dark brown. Rounded lateral posterior tubercle (tubercle bioluminescent) yellow. Ventral region dark brown; tarsi light brown or yellow.
Head (Figure 8D): Finely punctate, with deep longitudinal median anterior depression, continues posteriorly on longitudinal groove, vertex not V-shaped. Eye with dorsal margin sinuous with corrugated surface in lateral view.
Thorax: Subcylindrical prothorax (Figures 8A, B, C, F), almost as long as wide; margins sinuous; tubercles prominent; posterior half of pronotum with posterolateral oblong tubercle, posterolateral rounded tubercle (tubercle bioluminescent) and posteromedian rounded tubercle; anterior half of pronotum with anterolateral oblong tubercle, anterolateral rounded tubercle and anteromedian rounded tubercle. Pronotal sculpture consisting of fine punctations, almost imperceptible. Scutellum pentagonal; truncated at base; apical and lateral margin rounded; little longer than wide; margins subparallel; not carinate. Sclerites partially visible on lateral side of body. Antennal acetabulum shallow next to prosternal process. Prosternal process gradually attenuate towards posterior margin; margin more or less rounded. Elytra (Figures 8A, C, F) finely and sparsely punctated; margins parallel; apex acuminate; with several oblong tubercles, more or less longitudinally aligned; humeral tubercles more elevated; smaller and inconspicuous tubercles distributed on surface of the elytra.
Abdominal ventrites: Finely and sparsely punctated; ventrite 5 (Figure 8E) triangular, with longitudinal median carina, toothless; gradually narrowed from base to apex, which is truncated, not curved.
Female genitalia (Figure 8G): Baculum about 4 times as long as coxite; baculi separated by about three times width of baculum, at least in apical third. Coxites with setae present on lateral side.
Aedeagus: Paramere tapering as it approximates apex; acuminate at apex and with many setae. Penis tapering to apex; acuminate at apex, slightly curved ventrally in lateral view. Phallobasis about twice as long as paramere; about twice the paramere’s width. Concavity of phallobasis in dorsal view limited to base of phallobasis (based on Chassain & Touroult, 2013).
Sexual dimorphism: Males have: slightly more robust body; larger pronotal tubercles, more rounded and more well-defined margins; and more acuminate apically (Chassain & Touroult, 2013).
Intraspecific variation: Size variation (N = 1): length 25.60 mm; umeral width 7.70 mm.
Remarks. The punctuations of B. rugosus and B. schnusei are the finest and least dense into the genus: evident in the first and almost imperceptible in the latter. Balgus schnusei is the only species of the genus with setae on female coxites.
Balgus schnusei and Balgus schnusei cayennensis Chassain, 2003 can be differentiated by the combination of the following characteristics: B. schnusei has a slightly narrower body, the pronotum is only slightly wider than long, in B. schnusei cayennensis the pronotum is significantly wider than longer at the base; the dark triangular band near the elytra’s apex of B. schnusei is not present in B. schnusei cayennensis whose elytra are unicolor or with a slightly darkened apex; and the abdominal punctations is stronger in B. schnusei cayennensis (Chassain, 2003).
For Chassain (2003) these characteristics would be sufficient to delimit B. schnusei cayennensis as an independent species. However, the author had no male specimens analyzed, so the comparison of genitalia was not possible. Therefore, he did not risk creating a new species but rather a subspecies. Later Chassain & Touroult (2013) had access to B. schnusei cayennensis males, describing aedeagus, but did not raise this subspecies to a species level.
Chassain (2003) argues that the geographical distance between the sites of the original records of B. schnusei (Peru) and B. schnusei cayennensis (French Guiana) would be a support for the maintenance of the subspecies. However, B. schnusei is recorded for Brazil but without more precise information about the collection site (Vahtera et al., 2009). Lastly, B. schnusei was later recorded for Bolivia and this specimen corresponds morphologically to Peru’s holotype (Chassain & Touroult, 2013).
I believe that the characters listed by Chassain (2003) are not sufficient to create a subspecies, as well as the uncertainty about the extent of the geographical distribution of B. schnusei and B. schnusei cayennensis. We propose that B. schnusei cayennensis syn. nov. as a new junior synonym of B. schnusei.
Etymology. [Schnuse declined in dative mode]. In honor of entomologist von C. W. Schnuse.
Material examined. 1 ex., female, French Guiana, Saül, G. L. Tavakilian col., 21/VII/1982, C. Costa det., 1982, black light trap, MZUSP.
Distribution. Brazil, Bolivia, Peru and French Guiana (Figure 15).
Type locality. Peru, Meshahua, Valle Fluminis Urabamba, W.. Schuse col., 9/10/1903.
description: Published as part of Barbosa, Felipe Francisco, 2016, Revision and phylogeny of the genus Balgus Fleutiaux, 1920 (Coleoptera, Elateridae, Thylacosterninae), pp. 451-482 in Zootaxa 4083 (4) on pages 466-467, DOI: 10.11646/zootaxa.4083.4.1, http://zenodo.org/record/1050907