Microplinthus Zherichin, 1987

Meregalli, Massimo, 2020, Revision of the Nepalese genus Microplinthus Zherichin, 1987 (Coleoptera: Curculionidae: Molytinae), with description of 25 new species, Zootaxa 4794 (1), pp. 1-63 : 7-9

Microplinthus Zherichin, 1987

Microplinthus Zherichin, 1987: 37 . Type species: Microplinthus morimotoi Zherichin, 1987: 38 . Gender masculine. Alonso- Zarazaga & Lyal, 1999: 196. Meregalli, 2004: 609–627. Alonso-Zarazaga & al., 2017: 468.

Falsanchonus Zherichin, 1987: 28 . New synonymy. Type species: Falsanchonus ausobskyi Zherichin, 1987: 29 . Gender masculine. Alonso-Zarazaga & Lyal, 1999: 197. Meregalli, 2003: 323–335. Meregalli, 2004: 622. Alonso-Zarazaga & al., 2017: 468.

Microniphades Zherichin, 1987: 5 . New synonymy. Type species Microniphades schawalleri Zherichin, 1987: 5 . Gender masculine. Alonso-Zarazaga & Lyal, 1999: 197. Meregalli, 2004: 622. Alonso-Zarazaga & al., 2017: 468.

Redescription. Curculionidae : Molytinae : Euderini (formerly Aminyopini , as in Meregalli 2003) of small size (2.8–6.2 mm, the majority of species 3.3–4.5 mm), wingless.

Body ovate to elliptical to almost cylindrical; integument moderately glossy to matt, microsculpture very shallow to deepened, usually dark brownish, seldom reddish, in several species dark ferruginous. Vestiture consisting of scattered setae, seldom hair-like, usually slightly thickened towards apex, in some species spatulate, recumbent against integument or erect, from short to 3x as long as wide and longer than one elytral interval width, irregularly inserted on elytral intervals, usually longer and more closely placed on odd intervals, in some species thickened in tuft on elytral tubercles or humps; shorter scale-like setae usually also present on elytra.

Rostrum short and stout to moderately elongate, as long as pronotum or slightly longer, from moderately to strongly curved, in lateral view of equal thickness from base to apex, or, in some species with rostrum strongly curved, very distinctly thickened basad and slightly tapering apicad; base of rostrum in some species sinuate with respect to head; dorsum seldom almost smooth, usually more or less deeply and densely sculptured, with punctures and 3 or 5 longitudinal lines, sharp or barely visible, seldom absent; apex usually smooth and glossy, in many species reddish, often minutely punctate.

Head with underside linear in lateral view, median suture generally raised below gula. Epistoma flat, slightly sinuate inwardly at middle. Scrobes glossy, narrow, oblique; upper margin quite sharply delimited, reaching eye at middle of its anterior side; lower margin parallel to upper one, reaching underside of rostrum near base. Prementum moderately narrowed basad, its minimum width at least as wide as the basal part of the scrobes. Antennae sub-apical; scape clavate, often abruptly thickened at apex, usually with some erect setae on anterior side near apex; funicle 7-segmented, antennomeres 1–2 short or moderately elongate, 3–7 smaller, isodiametric or transverse; club ovate to elliptical, tomentose, 3-segmented, club antennomere 1 shorter than 2–3 together, annulus distinct but all sutures on club scarcely visible. One seta at apex of rostrum, lateral to epistoma; one seta at apex of pregenae; one seta at middle of mandible, basal, and one at apex of labium. Head short, globose, more or less punctured, moderately to deeply inserted into pronotum; vertex usually broader than base of rostrum; eyes lateral, ovate to elliptical, flat or weakly convex, small, with about 30 to more than 50 ommatidia.

Pronotum approximately as long as wide or slightly longer than wide, weakly convex on dorsum, base nearly straight or weakly curved towards elytra, sides weakly and regularly curvilinear, with maximum width at midlength or sublinearly broadened from base to apical third and sharply converging apicad; apical margin subtruncate, usually not or moderately protruded above head, in some species strongly prominent, often slightly emarginate inward at middle; in lateral view apical margin sub-truncate or with moderately developed post-ocular lobes, lobes distinctly developed in species with apex strongly protruding above head; dorsum and sides with variable sculpture, usually with punctures, large or small to very small, dense or spaced, regularly impressed or partly merged and with interspaces narrowly and irregularly raised; median line, if present, usually narrow, irregular, often only raised in anterior half. Scutellum not visible or minute.

Elytra oval or elongate; humeri not broadened; suture locked; base weakly arched, usually slightly broader than base of pronotum, seldom distinctly broader or narrower, as broad as base of pronotum; elytral sides subparallel or more or less curved, more curved in species with shortly oval elytra, maximum width at midlength or near base; dorsum flattened or weakly convex; declivity, in lateral view, regularly curving from dorsum, not sharply vertical. Striae 10, 1–9 complete from base to apex or at least to declivity, stria 10 very narrow, incomplete. Punctures in striae round or subquadrate, in many species dense and regularly aligned, as wide as or wider than intervals on dorsum, usually narrowed and shallower on declivity, in some species more spaced, shallow and irregularly delimited; interspaced between two punctures flat or in a few species with a small granule. Intervals flat or weakly convex, smooth or rugose, often with low elongate humps or high oblong tubercles; interval 5 interrupted at beginning of declivity, not or weakly raised at this point.

Prosternum more or less deeply incised, channel limited to anterior half; base before coxae often slightly swollen; intercoxal process acute, not developed. Mesosternum short, punctured, intercoxal process rounded apicad. Metasternum shorter than the width of middle coxae, punctured. Fore coxae round, contiguous; middle coxae round, barely separate; hind coxae transverse, separate. Trochanters with one seta. Ventrites 1 and 2 fused, 1 as long as 2, suture between 1 and 2 often slightly deepened on sides, scarcely distinct at middle; ventrite 2 longer than 3 and 4 together; these short, isomorphic; ventrite 5 approximately as long or slightly longer than 3 and 4 together, semicircular or more elongate, apex with two groups of setae at posterior-lateral margin, each group consisting of 2–3 setae, one of which often longer. Ventrites curvilinearly narrowed from 1 to 5 or almost subparallel from 1 to 3 and more narrowed between 4 and 5; 1, 2 and 5 variably punctured, punctures scattered or denser, generally interspaces among punctures at least almost as wide as punctures, in a few species with two very large pits on median part of ventrite 1, near apex; ventrites 3 and 4 nearly smooth; intercoxal process of ventrite 1 broad, subtruncate or subacutely produced.

Legs with femora densely punctured or wrinkled, weakly or moderately clavate, with a more or less distinct tooth at middle of inner side, seldom indistinct. Tibiae short, straight; fore tibiae with oblique or slightly sinuate or rounded apical fringe of setae; subapical fringe absent, inner premucro absent in both sexes, inner margin smooth or in some species denticulate towards apex. Middle and hind tibiae with ascending, sinuate fringe. Tarsi short, tarsomere 1 conical, 2 as long as wide, 3 bilobate, lobes scarcely to moderately developed; underside with incomplete whitish hairy pads and usually long marginal setae; onychium slender; claws free, narrow, widely divergent, inner teeth variable, from not present to microscopic, barely visible to strong, almost as long as half claws length.

Body of penis from flattened to strongly curved, in two species sinuate, dorsal side membranous, apex simple, rounded-ogival or elongate, in some species acutely tapering; endophallus minutely denticulate, lacking large sclerites; apodemes approximately as long as body of penis, flattened and slightly broadened in apical part; tegmen oval, with narrow strut and relatively well developed parameroid lobes.

Hemisternites cylindrical, styli slender; sternum VIII of female from weakly transverse to subquadrate to slightly elongate, arms fused for a short distance, seldom slightly longer, or completely independent, branches of apodeme always present, narrow or slightly thickened, from short to as long as arms, perpendicular to apodeme or curved downwards or X-shaped in continuity with arms.

Secondary sexual characters. Males and females are very similar. The only distinct secondary characters concern the shape of the ventrites: male ventrites 1 and 2 are generally flat or very weakly impressed medially, and ventrite 5 is subtruncate at apex; female ventrites 1 and 2 are slightly convex, anyway never impressed, and ventrite 5 is more regularly rounded at apex. There is no other sex-associated variation in the shape of other structures, such as rostrum, antennal insertion, or legs.

Distribution: The genus includes 42 species so far known, distributed in Nepal and northern India, with two species present on Mount Emei, in China: Sichuan. Detailed data on the distribution of the genus in the various regions of Nepal are given after the key.

Natural History: The majority of the specimens were collected in forest habitat, on the southern slopes of the Himalayan chain, at elevations between 2000 and 4000 m. Collecting methods were not usually detailed, but it seems likely that the beetles were found by litter sifting in forests or below Rhododendron shrubs. No information is available regarding the life cycle and the host plants of the larval stages.