Plastocerus thoracicus Fleutiaux, 1918

Hájek, Jiří, Ivie, Michael A. & Lawrence, John F., 2020, Binhon atrum Pic - a junior synonym of Plastocerus thoracicus, with nomenclatural notes on Plastocerus (Coleoptera: Elateridae: Plastocerinae), Acta Entomologica Musei Nationalis Pragae 60 (2), pp. 391-396 : 393-395

Plastocerus thoracicus Fleutiaux, 1918

( Figs 1–10 )

Plastocerus thoracicus Fleutiaux, 1918: 236 (original description).

Type locality:‘Environs de Tuyen-Quan’ [ Vietnam, Tuyên Quang Province, Tuyên Quang city, ca. 21°49′N 105°13′E].

Binhon atrum Pic, 1922: 29 (original description).

Type locality: Not specified in the description; ‘ Tonkin, Hoa Binh’ [ Vietnam, Hoa Binh Province, Hòa Bình, ca. 20°48′N 105°20′E] based on labels under the type specimen); syn. nov.

Type material. Plastocerus thoracicus : HOĿOŦΥΡΕ: ♂, not located in MNHN (A. Mantilleri, pers. comm. 2019). Binhon atrum : HOĿOŦΥΡΕ: ♀ ( Figs 1, 3 ), labelled: ‘Hoa Binh / Tonkin [hw Pic] // type [hw Pic] // TYPE [p, red label] // Binhon / ng. / atrum Pic [hw Pic]’ ( MNHN).

Additional material studied. CHINA: GUΑΝǤXι: 1♂, ‘China:Kwangsi [Guangxi], Hsiangshien 1935, G. Liu.’ ( ANIC; completely dissected); 1 ♀. YUΝΝΑΝ: ‘ China, Prov. / Yunnan,Gbg./ b. Mengtze .[= mountains near Mengzi]’ ( NHMB). VIETNAM: 8 ♂♂, ‘Hoa / Binh [hw Pic] // ♂ de / Binhon [hw Pic]’ ( MNHN); 1 ♂, ‘ Vietnam N / Tam dao 26.5.- 3.6.1986 / Vinh phu prov. / Strnad Jan lgt. [p]’ ( NMPC).

Diagnosis. Body elongate; total length:♂♂ 7–9 mm, ♀♀ 10– 12 mm. Colouration pitchy brownish-black; surface shiny with sparse greyish setation ( Figs 1, 3 ). Head coarsely and irregularly punctured, distance between punctures slightly greater than puncture diameter in depression between eyes, but much less than puncture diameter in other parts of head; eyes large, hemisphaerical; antennae with 11 antennomeres: scape large, pedicel ring-shaped, antennomeres 3–10 elongate with distinct rami, antennomere 11 long and slender; male with antennomeres 3–11 increasing in length (length ratios as follows: 4.0–1.0–2.0–3.0–3.3–3.5–3.9–4.4–4.5– 5.0–12.0), rami more than twice as long as length of respective antennomere; female with antennomere 3 longer than antennomeres 4–11 which are of same length (length ratios as follows: 3.5–1.0–2.7–2.3–2.3–2.3–2.3–2.3–2.3–2.3–2.3), rami of similar length to length of respective antennomere; mandibles slender, sickle-shaped, without additional teeth. Pronotum transverse, widest at anterior third; sides distinctly sinuate and explanate, posterior angles weakly produced; posterior edge with narrow median incision; disc convex, entire surface irregularly punctate, punctures finer and sparser medially on disc, becoming coarser and denser laterally ( Fig. 4 ). Prosternum transverse; prosternal process slender, apically slightly broadened ( Fig. 5 ); promesothoracic interlocking mechanism weakly developed. Elytra slightly broadened in apical fourth of its length, then attenuated to rounded apex; lateral margin visible except in anterior third; surface of elytra with more or less serial, irregular shallow depressions; punctation consisting of fine setigerous punctures placed both in depressions and on raised surface between them, punctures often clustered and confluent in depression, but sparse on other surfaces with distances between punctures much greater than puncture diameter. Metathoracic wing with venation as in Fig. 6 (female from China displaying remarkable aberration in one wing with bifurcation of vein MP 4, see Fig. 7 ; the other wing conforms with the male illustration). All legs slender; tarsi longer than tibiae, tarsomeres 1–4 decreasing in length, tarsomere 5 longest; claws simple. Male with seven ventrites (sternites III–IX), female with six ventrites; however, exposition of apical ventrite varying in both sexes. Male genitalia: aedeagus trilobate, penis narrowly acute at apex, parameres hooked subapically ( Fig. 8 ). Female genitalia: female abdominal sternite VIII as in Fig. 9 ; ovipositor long, slender, barely sclerotized; paraprocts about 4.5 times as long as gonocoxites, gonostyli present ( Fig. 10 ).

The two species of Plastocerus are similar morphologically, but differ in body colouration (uniformly blackish in P. thoracicus ; ochreous elytra with distinctly darker head and pronotum in P. angulosus ), shape of pronotum (widest anteriorly, with explanate sides, weakly produced posterior angles and posterior median incision in P. thoracicus ; widest posteriorly, with straight, converging, non-explanate sides, strongly produced posterior angles and weak posterior emargination in P. angulosus ), and differences in male genitalia (apex of penis subacute with finely rounded tip, parameres broad with ventral side almost straight, apex of paramere broadly obtuse in P. thoracicus ; apex of penis narrowly acute, laterally somewhat compressed, parameres slender with ventral side sinuate, apex of paramere narrowly obtuse in P. angulosus ).

Variability. Both the Vietnamese and Chinese specimens show slight variability in the shape of the explanate lateral part of pronotum, and in the punctation of the dorsal surface. However, with the limited material available, we consider the differences as intraspecific variability.

Comments to classification. FĿΕUŦıΑUΧ (1918) described Plastocerus thoracicus based on a single male from ‘Tonkin’ (northern Vietnam), without any mention of its relationships with either the Mediterranean or American taxa. However, FĿΕUŦıΑUΧ (1940) mentioned the species in combination with Ceroplastus , linking it with the Mediterranean Plastocerus angulosus . The species is well characterised by its blackish colouration and especially the explanate medial parts of the sides of pronotum (cf. Figs 1 and 3 ). Unfortunately, the type specimen could not be located in the collection of MNHN (A. Mantilleri, pers. comm. 2019) thus the direct comparison of both holotypes is not possible. Nevertheless, as Binhon atrum fits completely with current concept of Plastocerus Schaum and to the description of P. thoracicus , and no other Plastocerus species is known from North Vietnam or neighbouring countries, there is little doubt that Plastocerus thoracicus and Binhon atrum are conspecific. Therefore, we establish the following new synonymies: Plastocerus Schaum, 1852 = Binhon Pic, 1922 , syn. nov., and Plastocerus thoracicus Fleutiaux, 1918 = Binhon atrum Pic, 1922 , syn. nov.

Distribution. Plastocerus thoracicus is so far known only from northern Vietnam (provinces of Hoa Binh, Tuyên Quang and Vính Phúc), and here it is recorded for the first time from southern China (Yunnan and Guangxi).

Figures

Figs 1–3. Plastocerus thoracicus Fleutiaux, 1918. 1 – female holotype of Binhon atrum Pic, 1922; 2 – labels of the type specimen; 3 – males of Binhon (Vietnam, Hoa Binh).

Figs 4–10. Plastocerus thoracicus Fleutiaux, 1918. 4 – detail of male head and pronotum (Vietnam, Tam Dao); 5 – prosternum (China, Yunnan); 6 – metathoracic wing (Vietnam, Tam Dao); 7 – metathoracic wing (China, Yunnan); 8 – aedeagus (Vietnam, Tam Dao); 9 – female abdominal sternite VIII (China, Yunnan); 10 – ovipositor (China, Yunnan). Scale bars 1 mm.