Metallactus sekerkai, Sassi, 2015

Sassi, Davide, 2015, Two new species of Metallactus from Bolivia and Brazil (Coleoptera: Chrysomelidae: Cryptocephalinae), Acta Entomologica Musei Nationalis Pragae 55 (2), pp. 703-712 : 704-707

Metallactus sekerkai sp. nov.

( Figs 1–3, 7 , 9–11, 15–16 , 18–19, 22 )

Type locality. Bolivia, Department of Santa Cruz, Florida Province, Refugio Los Volcanes (5 km NW of Bermejo), 18°06.3′S, 63°26.0′W, 1050–1150 m a.s.l.

Type material. HOLOTYPE: J, ‘ Bolivia Santa Cruz dpt. Florida pr. 1050-1150 m Refugio Los Volcanes 18°06.3’S, 63°26.0’W beating of vegetation L. Sekerka lgt. 10.-14.xii.2011 ’ [white label, printed] // ‘ Metallactus sekerkai sp. nov . Holotypus D. Sassi des.’ [red, printed] ( NMPC). PARATYPES: 2 JJ 2 ♀♀, same data as the holotype ( NMPC, LSPC, DSCI) ; 1 J 1 ♀, ‘ Bolivia, Santa Cruz Above Achira Rd to Floripondo 1900 m 10 December, 2011’ [white label, printed] // ‘ 18°09‘ S 63°47‘ W Bonaso, Morris & Wappes’ [white, printed] ( JWAT, MNKM). All paratypes provided with additional label: ‘ Metallactus sekerkai sp. nov . Paratypus D. Sassi des.’ [red, printed].

Description of male. Habitus in Figs 1–3, 7 . Body length: 5.50–5.75 mm; interocular distance equals to 9.2 % of total body length (measures are average values taken on three specimens). Body cylindrical, slender, elongate. Head, yellow, with reddish patches on vertex, insertion of antennae and lower part of clypeus; vertex sparsely and minutely punctate; interocular median longitudinal line very distinctly impressed; frontoclypeal suture sometimes marked by two distinct, oblique rows of punctures, frontoclypeal punctures coarse and generally gathered along inner ocular rim; ocular lines long and coarsely punctate; eyes moderately prominent when observed from above; antennae black, only apex of antennomeres I–IV yellowish; length ratio of antennomeres: 100: 60: 100: 140: 170: 180: 180: 180: 170: 170: 170. Pronotum yellow with two longitudinal reddish bands, slightly angulate on inner rim, extending from apical to basal margin; sides only slightly arcuate and thus lateral margins completely visible from above; punctation coarse and sparse, almost absent on median area of disk; barely perceptible transverse impression along each sides of median line, close to posterior margin.

Scutellum dark yellow to red towards apex, quite stout, sides barely convergent so the surface is almost equal in width, apex regularly rounded.

Elytra parallel-sided, distinctly wider than pronotum, yellow, two large longitudinal reddish bands extended from base toward apex, in continuity with those on pronotum, bands are slightly concave on outer sides, tapered posteriorly and not reaching apex; postscutellar area regularly even, not forming tubercle ( Fig. 7 ), elytral punctation fairly impressed, punctures similar in size and shape to that of pronotum, arranged in quite regular rows, slightly less impressed towards apex, rows barely recognizable on periscutellar area and behind humeri; interstices flat and lustrous.

Legs normally shaped, reddish, apex of tibiae and tarsi black; tibiae sparsely covered with whitish setae; tarsi not particularly enlarged. Ventrites reddish with large marginal band on abdominal ventrites and pygidium yellow; whole ventrites and pygidium with sparse, whitish setae. Prosternal process ( Fig. 16 ) broad, surface strongly and densely punctate, covered by long and whitish setae, deeply impressed in middle, with sides abruptly rising, and strong acute denticle in middle of apical margin. Fifth abdominal ventrite with shallow but distinct bare oval and lustrous depression, posterior margin fairly notched.

Median lobe of aedeagus ( Figs 9–11 ) widened towards apex, marginal apex evenly curved, setose on sides, devoid of apical tooth, ventral surface with couple of barely perceptible shallow depressions on apical half, delimiting faint and short median carina; ostium basally delimited by couple of slender frenula, separated apart by membranous area; in lateral view apical half bulging and apex fairly bent ventrally.

Females differ from males in stouter body, body length 6.50–6.75 mm, interocular distance equals to 12.7 % of total body length (measures are average values taken on two specimens), shorter antennae, prosternal process more robust and wide, its median tooth more prominent beyond posterior margin ( Fig. 15 ). Anal ventrite with small, deep, slightly transverse pit, reaching posterior margin of anal ventrite.

Rectal apparatus ( Figs 18–19 ) with two dorsal and one ventral sclerites; dorsal sclerites narrow, tapered towards median line, apodemes quite large but hyaline, bent upwards and leaning against rectum, thus barely visible from above, transverse connection across dorsal fold sinuate in middle; ventral sclerite large, ribbon-like, slightly tapered on sides, more pigmented in middle, with rounded apodemes wider than rectum; lateral fold barely pigmented, devoid of sclerotizations.

Spermatheca ( Fig. 22 ) U-shaped, slightly pigmented; basal part not swollen; base not reflexed, gland and duct insertions not sclerotized; ductus long, slender and coiled, its insertion on bursa copulatrix slightly enlarged and clearly pigmented.

Differential diagnosis. The new taxon in terms of size and shape of the body approaches some species of the first group of SUFFRIANʼs (1866) system, and in particular M. minax Suffrian, 1866 is similar. However, the latter species is fairly differently coloured and has weaker pronotal and elytral punctation. The median lobe of the aedeagus is also completely different in M. minax , having a massive bulge on its ventral side. With regards to the chromatic pattern, some specimens resemble M. abbreviatulus Suffrian, 1866 , which is stockier, with pronotal punctation almost obliterated on the shiny surface and elytral punctures finer and denser. Metallactus abbreviatulus also differs in the shape of the prosternal process, and absence of the denticle in the middle of the apical margin. Metallactus albivittis Suffrian, 1866 has a similar colouration too, but is slender and more coarsely punctate, especially on the pronotum and the frons. Besides, the interocular distance is greater in males of M. albivittis .

Etymology. The species is dedicated to Lukáš Sekerka, specialist in Coleoptera , particularly Chrysomelidae , and collector of most of the specimens.

Biology. The type locality, situated on the slopes of the so-called ‘Elbow of the Andes’, is a unique place where several ecoregions meet and result in high biological diversity.According to recent collecting efforts, the locality contains numerous undescribed leaf beetles whose distribution seems to be limited; a few of them have been recently described, along with detailed characterization of the locality ( SEKERKA & WINDSOR 2012, SEKERKA et al. 2014). All specimens from Refugio Los Volcanes were collected by beating of flowers of a small tree, supposedly belonging to the Euphorbiaceae , growing on the edge of evergreen premontane forest situated at the bottom of valley near the river at 1050 m a.s.l. (L. Sekerka, pers. comm.). The two specimens from Achira were collected by beating of vegetation along the road. The locality is situated approximately 20 km (air) west of Refugio los Volcanes and is formed by patches of forest scattered among pastures and crop fields.

Distribution. Bolivia (Santa Cruz).

Taxonomic remarks. The shape of the prosternal process ( Figs 15–16 ), posteriorly terminating in a well marked tooth, is unusual in the genus Metallactus and is reminiscent of some species currently included in the genera Sternoglossus Suffrian, 1866 * and Mastacanthus Suffrian, 1852 . SUFFRIAN (1852, 1866) attributed great importance to the shape of the prosternum in establishing new genera in Neotropical Pachybrachina . In fact, the division into groups on the basis of this criterion has never been tackled by any subsequent authors (e.g. CHAPUIS 1874, JACOBY 1888 –1892, RILEY et al. 2002, CHAMORRO- LACAYO & KONSTANTINOV 2004, CHAMOR- RO- LACAYO 2013, BARNEY et al. 2013). After comparing this character among several dozen species of Pachybrachina from the Neotropical Region, I noticed a high degree of variability in the shape of the prosternum. Presently, I do not think that the sharing alone of single similarities in the morphology of the prosternal process could yield a correct taxonomical setting based on solid phylogenetic criteria.

Figures

Figs 1–8. 1–3, 7 – Metallactus sekerkai sp. nov.: 1 – holotype; 2 – female, typical chromatic form; 3 – female, chromatic variation; 7 – holotype, lateral view. 4–6, 8 – M. quadriophthalmus sp. nov.: 4 – holotype; 5 – male, chromatic variation; 6 – female; 8 – holotype, lateral view. Abbreviation: psa = postscutellar area. All the figured specimens come from their respective type localities. Specimens are not figured to the same scale.

Figs 9–17. 9–11, 15–16 – Metallactus sekerkai sp. nov. 12–14, 17 – M. quadriophthalmus sp. nov. 9–14 – apex of median lobe of aedeagus (9, 12 – ventral, 10, 13 – dorsal, 11, 14 – lateral views); 15–17 – prosternal process: (15 – female; 16–17 – male).

Figs 18–23. 18–19, 22 – Metallactus sekerkai sp. nov. 20–21, 23 – M. quadriophthalmus sp. nov. 18–21 – female rectal apparatus (18, 20 – dorsal, 19, 21 – ventral views); 22–23 – spermatheca.