Pachystethus Blanchard 1851
Creators: name: Ramírez-Ponce, Andrés
name: Morón, Miguel Angel
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Rutelidae
Pachystethus

description: Genus Pachystethus Blanchard, 1851
(Figs. 1–54)
Type species. Popillia vidua Newman, 1838 by monotypy.
Gender. Masculine.
Description. Total body length 7–12 mm, humeral width 4.0– 4.5 mm. Body robust, slightly depressed, dorsal surface shiny and glabrous. Head: clypeus subtrapezoidal or subrectangular, borders slightly upturned, disc surface rugopunctate, coarse and dense punctures. Frons with weak, wide central protuberance and small lateral depressions between extremes of frontoclypeal suture and the base of ocular canthus; frontoclypeal suture straight (best seen in species with contrasting coloration, but hidden under irregular texture and dark color in other species). Eyes small, ovate, circumocular depression accentuated. Ocular canthus wide and glabrous. Mouthparts (Figs. 32–35): fully developed; mandibles with three teeth, wide molar area; maxilla with six teeth, long, straight, sharply pointed, not fused. Antennal club long (as long as the length of all preceding antennomeres combined) with lamella straight or distally curved inward. Pronotum subtrapezoidal, weakly convex; one small, lateral pit at each side; lateral borders slightly angled or rounded; posterior border without margin; posterior angles straight; anterior border with membranous rim, anterior angles rounded; basal section wider than mesial, as wide as elytral base; disc surface with scattered minute punctures or with irregular, large, deep punctures. Distance between mesocoxae wide, meso-metasternal process well developed, wide, rounded at apex, directed forward or slightly directed downward; overhanging the bases of mesofemora; meso-metasternal suture not evident. Elytral surface weakly marked by discontinuous, small punctures or deeply marked by striae; elytral suture flattened or partially raised, spine-like apex; preapical slope shortened; humeral and apical calli well developed; epipleural border as long as 2/ 3 of total length of elytral border (epipleural border in females thickened and expanded laterally). Scutellum flattened, glabrous, acute apex. Abdomen depressed, anal plate in males with apical margin entire. Propygidium striate, completely covered with elytra. Pygidium uniformly convex, surface striate, partially covered by apex of elytra, apical border acute, with long setae. Protibiae bidentate in both sexes. Protarsomeres 1–4 shortened; protarsomere 5 with ventral denticle not evident; protarsomeres 3–5 with ventrolateral longitudinal keels; protarsal empodia with two long setae, onychium partially hidden; apex of protarsal inner claw deeply cleft, lower denticle more than two times wider than upper denticle; apex of protarsal outer claw entire, sharply acute but with basal part swollen. Mesotibiae and metatibiae slightly swollen at middle. Apex of mesotarsal outer claw narrowly cleft, apex of mesotarsal inner claw entire. Apex of both metatarsal claws entire. Male genitalia: parameres much shorter than basal piece, sagitally separated and each one divided in an upper part more or less upturned apically; lower part fused with ventral plate. Tectum with prominent basal calli. Spiculum gastrale “Y” shaped, basal part straight and shorter than lateral sclerites; associated plates proportionally larger. Sexual dimorphism: males with protarsomere 1 reduced, as long as the length of protarsomeres 2–4 combined. Protibia widened with lateroapical denticle shortened. Antennal club longer than length of all other antennomeres combined. Females: protarsomere 1 long, longer than the length of protarsomeres 2–4 combined. Protibia not widened with lateroapical denticle enlarged. Antennal club as long as length of the preceding five antennomeres combined. Frequently each sex displays different color patterns.
Diagnosis. Anomalini with body robust, slightly depressed, dorsal surface shiny and glabrous; protarsus shortened and swollen; protarsomere 5 without or with very reduced ventral denticle; meso-metasternal intercoxal region wide and increased projection; male antennal club as long as the length of all preceding antennomeres combined; epipleural border widened; and parameres sagittally separated. Species of Pachystethus are separated from species of Callistethus based on the meso-metasternal process that does not reach the procoxae and its apex is not acute and frequently directed upwards. Species of Pachystethus are separated from species of Paranomala based on the absence of posterior pronotal margin (present in Paranomala), protarsomeres shortened and widened, the length of first to fourth protarsomeres is similar to fifth (protarsomeres not shortened nor widened in Paranomala, the length of the first to fourth protarsomere clearly longer than fifth), apex of elitral suture spiniform (apex of elitral suture rouded in Paranomala), flattened body (body not flattened in Paranomala) and male genital capsule markedly angled (male genital capsule not markedly angled in Paranomala).
Distribution. Eastern and southeastern Mexico to central Guatemala.
Remarks. The unusual and complicated history of these species and genera is mainly derived from the misidentification of sexes that exhibit a marked dimorphism in coloration, which caused nomenclatural complications as stated by Arrow (1899) and that will be discussed and resolved in next sections. Besides being synonymized with Paranomala (Lacordaire 1856, Bates 1888, Ohaus 1918, Blackwelder 1944, Machatschke 1972, Potts 1974) and Callistethus (Machatschke 1957, Morón 1997, Micó et al. 2003), the genus Pachystethus has also been synonymized with Spilota (Casey 1915), placed as a subgenus of Anomala (Frey 1968), or synonymized with Callistethus (Machatschke 1957, Morón 1997, Micó et al. 2003). Among Callistethus and some species considered as Spilota (as well as with other genera like Strigoderma, Epectinaspis, or Callirhinus), morphological characters that Pachystethus shares with these genera are the prominent and wide meso-metasternal process, depressed and robust body, elytra reduced towards apex, apex of elytral suture spiniform, pronotum without posterior margin, and evident sexual dimorphism. Therefore, it might be more appropriate to assume that Pachystethus would have closer affinity with some of the latter genera than with Paranomala.
Larvae. According to the description provided by Micó et al. (2003) the diagnostic characters for the larva of Pachystethus nectoctenus (cited as Callistethus vidua) are: head with two posterior frontal setae on each side; dorsa of abdominal segments VII–IX each with poorly-defined transverse rows of slender long setae, alternated with medium-sized setae; semicircular furrow on dorsum of last abdominal segment nearly absent; lower anal lip with 20–21 setae; raster with 9–12 acute, slender pali on each palidium, palidia diverging posteriorly, and with 25 preseptular hamate setae. It is possible that the development of semicircular furrow on abdominal segment X may be an important generic character for Anomalini. Main differences with larvae of Paranomala, Anomala, and Strigoderma are in the distribution of setae on the dorsa of abdominal segments VII–IX, the presence of dorsal furrow on last abdominal segment, and composition and form of palidia. But larval descriptions of additional species of Pachystethus, Strigoderma, Callistethus, and Paranomala are required before precise larval diagnosis may be completed.
description: Published as part of Ramírez-Ponce, Andrés & Morón, Miguel Angel, 2012, Revision of the genus Pachystethus Blanchard with description of three new species from Mexico (Coleoptera: Scarabaeidae: Rutelinae: Anomalini), pp. 1-24 in Zootaxa 3394 on pages 2-4, DOI: 10.5281/zenodo.210542