Homalochilus Blanchard 1851
Creators: name: Cherman, Mariana A.
name: Basílio, Daniel S.
name: Clarkson, Bruno
name: Agostinis, André O.
name: Smith, Andrew B. T.
name: Vaz-De-Mello, Fernando Z.
name: Almeida, Lúcia M.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Scarabaeidae
Homalochilus

description: Genus Homalochilus Blanchard, 1851
(FIG. 4A–H)
Homalochilus Blanchard 1851: 172 (original description); Lacordaire 1855: 270 (redescription); Harold 1869: 1141 (catalogue); Bruch 1911: 201 (catalogue); Dalla Torre 1913: 319 (catalogue); Blackwelder 1944: 228 (catalogue); Gutiérrez 1952: 211–212, 213 (redescription, key); Smith 1987: 62 (catalogue); Evans 2003: 11, 206 (systematics, catalogue); Evans and Smith 2005: 170 (catalogue); Evans and Smith 2009: 174 (catalogue); Katovich 2008: 7 (systematics); Krajčík 2012: 128 (catalogue); Cherman et al. 2016: 765 (systematics); Cherman et al. 2017:18 (systematics).
Type species: Homalochilus punctatostriatus Blanchard, 1851 (here designated) [using Article 70.3.2 of the International Code on Zoological Nomenclature, 1999 to correct the misidentification of that species as Homalochilus niger by both Gutiérrez (1952: 213) and Evans (2003: 11)]. See details on Homalochilus monophyly, composition, and remarks in the systematics’ section (Discussion).
Taxonomic history of Homalochilus
Blanchard (1851) described Homalochilus based on two species: H. niger and H. punctatostriatus, both collected by M. d’Orbigny at the Patagonian Baie San-Blas (Bahia San Blas, southern Buenos Aires, Argentina). The author allied this genus mainly with Diplotaxis, with differences in the labium and the shorter body length. Some features mentioned by Blanchard (1851) present in both species of Homalochilus are: body coarsely punctate; clypeus broad, lamina-shaped; distal palpomere of maxilla oval; labium wide, enlarged laterally and truncate on apex, palpi inserted ventrally; prothorax wide; and elytra with apex rounded. The generic description (Blanchard 1851) stated other features found only in H. punctatostriatus: antennae with nine antennomeres; scutellum triangular; maxilla with two teeth on galea (H. niger has four); and the elytral apex rounded. This author also mentioned that the tarsi are cylindrical, not enlarged. This feature is controversial, as he used female syntypes (Figs 5B, C, 7B, F) to describe each species, and enlarged tarsi is a dimorphic character in males of several species among Melolonthinae.
Lacordaire (1855) allied Homalochilus almost entirely with Liogenys except that the maxillary palpi are shorter and wider, distal palpomere thick, oval, acuminate, and without fovea; head short, frons swollen and sloping on vertex; and in the clypeus rounded and weakly flanged. Different from what was stated by Lacordaire (1855), Homalochilus species do have fovea on the maxillar distal palpomere. Lacordaire (1855) mentioned proand mesotarsi weakly enlarged with pads in males, so we infer that he was referring to a series of H. niger with males and females.
Ohaus (1911) described Astaena bicolor from a series of seven specimens collected in Córdoba (Argentina). Some of these specimens had been already identified as A. discoidalis Burmeister by both Burmeister and Stempelmann, and others as ‘ A. bicolor Burm. ’, the latter specimens belonged to W. Günther. Based on the identification label of these specimens bearing ‘ A. bicolor ’, Ohaus described this species, and stated his doubt about the generic position due to the toothed mandible, which does not match with those of Astaena. According to Ohaus (1911), the diagnostic features of A. bicolor are: body convex, black, weakly shiny, elytra red with margins black; clypeus large and trapezoidal, frons and vertex coarsely punctate and opaque; antenna with nine antennomeres; prothorax narrowed along its anterior margin; pronotal anterior corners projected; scales intercalated with bristles all along the pronotal margin; scutellum flat or depressed, smooth; elytra with sutural ridge bearing scattered, microscopic, yellow bristles, and apex bearing four-to-five brown, erect bristles; mesosternum reduced; propygidium very long, longer than pygidium, both equally punctate and covered with white, thick scales on the anterior margin, as well as the thorax and ventrites ventrally; tarsi cylindrical, slender; first tarsi with simple claws; mesotarsi and metatarsi with bifid claws.
Bruch (1911) reported H. niger and H. punctatostriatus from ‘Patagonia’ and expanded the distribution of Astaena bicolor Ohaus to Tucumán (Argentina).
The Blackwelder (1944) catalogue stated ‘Patagonia’ as the locality for both species of Homalochilus.
Gutiérrez (1952) revised Homalochilus due to the ‘insufficient diagnoses of Blanchard (1851) ’, and redescribed it based on the original descriptions and non-type specimens from Bruch’s collection housed at MACN. Gutiérrez (1952) suggested that the mandibles in A. bicolor are more alike to macrodactylines than those of sericines, as stated early by Ohaus (1911). Gutiérrez (1952) synonymized A. bicolor with H. punctatostriatus and justified this nomenclatural act stating that specimens of A. bicolor are the males of H. punctatostriatus females, which was confirmed by Juan B. Bosq from the MACN. With this matching, Gutiérrez confirmed that, contrary to what was stated by Lacordaire (1855), males of H. punctatostriatus do not have enlarged tarsi. Gutiérrez (1952) suggested that Lacordaire (1855) had been referring to males of a Catamarquian series of Liogenys morio Burmeister instead of H. punctatostriatus (see Liogenys niger comb. nov. further in this text). Gutiérrez (1952) presented a key to genera of ‘Liogenyina’ (Homoliogenys Gutiérrez, Manonychus Moser, Homalochilus, Liogenys, and Pacuvia) and redefined Homalochilus. In his diagnosis, Gutiérrez (1952) added new features and corrected others, as follows: frontoclypeal suture absent (considered present in the present work); inferior portion of eyes much larger than the upper; club as long as the funicle, shorter in females; short maxilla, galea bearing two teeth, distal palpomere fusiform (no mention about the fovea, which is present); pronotal anterior corners acute and projected, posterior corners rounded, scutellum 1.5 times longer than the width, apex acute; elytra short, enlarged on posterior third; subapical callus weakly marked; apical margin of each elytron rounded; fifth ventrite slightly longer than the others; propygidium very large and exposed, fused with tergite; mesotibia and metatibia with transverse carina complete, stronger in females; tarsi slender, cylindrical in both sexes; two metatibial spurs strongly uneven, the longest twice the length of the tibial diameter; claws bifid; in males the protarsal claws simple. Gutiérrez (1952) also expanded the geographic distribution of Homalochilus within Argentina, until then known only from Buenos Aires and ‘Patagonia’, to Jujuy, Catamarca, Santiago del Estero, La Rioja, Mendoza, and Cordoba provinces. Gutiérrez (1952) based the redescription of H. niger on a population from Jujuy composed of entirely black specimens similar to H. punctatostriatus (for more details see description of H. nigripennis). According to this author, the main features to distinguish H. niger (sensu Gutiérrez in this paragraph) from H. punctatostriatus are the size, the former being slightly larger; the elytra in colour, entirely black (H. niger) or red with margins black (H. punctatostriatus); and the ventral pubescence, bristled in thorax, lateral and disc of ventrites (H. niger) or scaly at these points, mainly on anterior margins of each ventrite (H. punctatostriatus).
Evans (2003) designated H. niger as the type species of Homalochilus, which had been previously done by Gutiérrez (1952), but neither of them examined the primary types.
Cherman et al. (2016) tested the phylogenetic relationships among the Diplotaxini, and Homalochilus was recovered as monophyletic, supported by the following characters: elytral disc without pubescence (character 63); pygidial disc without bristles (character 129), and antennal club shorter than funicle. Though, in that analysis the characters were coded with the syntypes, which are females and are in poor conditions of conservation. Hence, the monophyly of Homalochilus obtained in that work is not reliable enough due to the number of missing states.
Etymology
From Ancient Greek ὁμαλός (homalós, ‘even, level’); χείλoς (keilos, ‘lip’) = labrum (Harold 1869); masculine in gender.
Diagnosis
Homalochilus is distinguished from other Neotropical Diplotaxini by the following combination of characters: body short, sides parallel; black in colour, unicolorous or bicoloured (Figs 5A, 6A); frons very wide, eyes barely seen dorsally, most surface ventrally (Fig. 4A, B); labrum with medial emargination deep in frontal view, (37:1) (Fig. 4C); maxilla curved (14:1), galea with two teeth (Fig. 4D); labium quadrangular, ligula and mentum fused (30:1), angles of ligula laterally projected behind the palp (29:0) (Fig. 4E); antennae uniformly black, with nine antennomeres (40:1), club as long as the funicle or shorter (128:1); pronotal anterior corners fused with hypomeron (Fig. 4B); mesocoxae slightly separated (81:0) (Fig. 4H); elytra flattened, short, leaving the propygidium exposed (Fig. 5E); long, four to five erect setae on each inner margin on apex of elytra (Fig. 4F); ventrite V longer than ventrite IV (105:0) (Fig. 4H); in males tarsomeres cylindrical (77:1) and ventral pads absent (78:1) in all legs (Fig. 4G); parameres with split beyond the midline (153:2).
Redescription
Length: 7.6–9.8 mm; width: 4.0– 5.2 mm. Body short, semiopaque, sides parallel, body, head, and pronotum black, elytra red on disc and black on margins (H. punctatostriatus) or entirely black (H. nigripennis). Head: frons almost as wide as the anterior margin of pronotum; eyes almost entirely placed laterally, ventral portion larger than dorsal portion (Fig. 4A, B); frons and clypeus coplanar; clypeus truncate (H. punctatostriatus) or rounded, subemarginate (H. nigripennis); galea of maxilla curved with two teeth, the apical the strongest (Fig. 4D); distal maxillary palpomere acuminate, fovea deep, almost sulcate, extending reaching the midline of the palpomere or extending past (Fig. 4C); labium widened at the transverse midline, slightly wider than it is long; sloped from the transverse carina towards apex (Fig. 4E); apical emargination wide and rounded; two labial palpomeres, the basal longer; antenna with nine antennomeres; black in colour; club as long as or shorter than the funicle. Prothorax: pronotal anterior corners scaly, fused with hypomeron; pronotal disc coarsely punctate, simple punctures sparsely disposed; posterior corners subangulate to sharp, obtuse angulate. Pterothorax: scutellum triangular, long; metacoxae equal in length or slightly shorter than the distance between mesocoxae and metacoxae. Elytra: flattened, glabrous, or with scattered bristles, length from 1.5 times up to two times that of the pronotum; four elytral ridges, the one or two outermost less noticeable; subapical callus strong, at the same level of the posterior inner corner of the sutural ridge; four to five erect setae on each inner margin on apex of elytra. Legs: three protibial teeth, the basal shorter than the other two, the apical obtuse in relation to longitudinal axis (Fig. 4G); mesotibia cylindrical, two transverse carinae, the apical complete in both sexes; all tarsi simple, protarsomere I slightly shorter than protarsomere II in both sexes. Abdomen: propygidium exposed, scaly in basal region, mostly glabrous; pygidium flat, as wide as it is long; subquadrate or subtrapezoidal; pygidial disc glabrous, scaly basally.
Dimorphism
Male: metatibial spurs strongly uneven, the longest almost twice as long as the diameter of the tibial apex (Figs 5F, 6E); protarsal claws simple (Fig. 4G), mesotarsal and metatarsal claws bifid, parameres with basal region strongly sulcate, basally widened and slightly inflated, parameres abruptly narrowed and dorsoventrally bent after the midline, width uniform towards the apex, apex curved downwards (Figs 5G, H, 6F, G).
Female: metatibial spurs uneven, the length of longer spur almost 1.5 the diameter of the tibial apex; all claws bifid.
Composition
Homalochilus punctatostriatus and Homalochilus nigripennis.
Geographical distribution
ARGENTINA (Salta, Jujuy, Tucumán? [according to Gutiérrez (1952)], Catamarca, Santiago del Estero, La Rioja, Santiago del Estero, Córdoba, San Luis, Mendoza, and Buenos Aires).
Remarks on Homalochilus phylogenetic relationships Homalochilus is the sister-clade of almost all Neotropical Diplotaxini, except for Pacuvia. It differs from (Pachrodema + (Careocallus) + Liogenys )) in the frontoclypeal division complete (5:0), labium fused with ligula (30:1), apex never wider than the base (22:1); mentum without well-defined concavity on disc (32:1); and apex of metatibia not projected in males (142:1). At least nine of the diagnostic features of Homalochilus support the branch of the genus (Figs 1–3; Table 1). Characters that it has in common with other Neotropical Diplotaxini are: clypeus subemarginate (Pachrodema); frontoclypeal suture present, barely distinguishable (Pachrodema); nine antennomeres (a few Liogenys); base of sutural ridge of elytra along the entire scutellar margin (65:0) and first gap of elytral ridges less than two times the width of one ridge (66:1) (both latter characters shared only with Careocallus); mesotibia and metatibia with transverse carina complete in both sexes (some Liogenys and some Pachrodema); Character 84:1 (Table 1), was exclusive to Liogenys until the present analysis, and it is now shared with Homalochilus.
IDENTIFICATION KEY TO HOMALOCHILUS SPECIES [MODIFIED FROM GUTIÉRREZ (1952)]
1. Anterior margin of clypeus widely truncate (Fig. 5B); elytra red on disc and black on outer margins, less than twice the length of pronotum (Fig. 5A); anterior margin of ventrites covered with scales (Fig. 5D) .............................................................. ........................................................................................................................................................................ Homalochilus punctatostriatus
-. Anterior margin of clypeus medially subemarginate (Fig. 6B); elytra entirely black, slightly more than twice the length of pronotum (Fig. 6A); anterior margin of ventrites glabrous or with bristles (Fig. 6C) .......................... Homalochilus nigripennis
description: Published as part of Cherman, Mariana A., Basílio, Daniel S., Clarkson, Bruno, Agostinis, André O., Smith, Andrew B. T., Vaz-De-Mello, Fernando Z. & Almeida, Lúcia M., 2024, New and revised taxa of Neotropical Diplotaxini (Coleoptera: Melolonthidae): do they change the existing relationships? Revisiting systematics with morphological and molecular data, pp. 98-135 in Zoological Journal of the Linnean Society 201 (1) on pages 109-112, DOI: 10.1093/zoolinnean/zlad115, http://zenodo.org/record/11241094