Contribution to the knowledge of the Neotropical canopy dwelling genus Onorius

Frolov A. V., Akhmetova L. A., Vaz-de-Mello F. Z. 2019. Contribution to the knowledge of the Neotropical canopy dwelling genus Onorius (Coleoptera, Scarabaeidae, Orphninae): another species from southern Ecuador and notes on the hind gut morphology in the Orphninae. Journal of Natural History. 53 (17–18): 1071–1077.

DOI: 10.1080/00222933.2019.1632952


Contribution to the knowledge of the Neotropical canopy dwelling genus Onorius (Coleoptera, Scarabaeidae, Orphninae): another species from southern Ecuador and notes on the hind gut morphology in the Orphninae


Frolov, A.V.1,2, L.A. Akhmetovaand Fernando Z. Vaz-de-Mello2

1Laboratory of Insect Systematics, Zoological Institute, Russian Academy of Sciences, Universitetskaya nab., 1, St.-Petersburg, 199034 Russia. Email:

2Universidade Federal de Mato Grosso, Instituto de Biociências, Departamento de Biologia e Zoologia, Av. Fernando Corrêa da Costa, 2367, Boa Esperança, 78060-900 Cuiabá, MT, Brazil.


The generic status of Neotropical Orphninae genus Onorius Frolov et Vaz-de-Mello is supported by the discovery of another species in south-eastern Ecuador. The new species differs from O. inexpectatus Frolov et Vaz-de-Mello in the body sculpture and colouration. Both species have two large diverticula in the proximal part of the ileum; such structures are not found in the other members of the Aegidiini and are supposedly autapomorphic for Onorius.


The New World scarab beetles of the subfamily Orphninae (Coleoptera: Scarabaeidae) were separated in the tribe Aegidiini by Paulian (1984). Originally the tribe comprised four genera, Aegidium Westwood, 1845, Aegidiellus Paulian, 1984, Aegidinus Arrow, 1904, and Paraegidium Vulcano, Pereira et Martínez, 1966. Recently, a fifth genus, Onorius Frolov et Vaz-de-Mello, 2015, was described from O. inexpectatus Frolov & Vaz-de-Mello (2015). Although definitely a member of the Aegidiini, Onorius shows some unique characters not found in the other orphnine taxa: less prominent mandibles (weakly visible or invisible in dorsal view), labrum hidden under the clypeus, and the more robust and densely punctate tarsi with tarsomere 1 being relatively short (subequal in length to tarsomere 5), and tarsomere 5 relatively robust and wider in lateral view than the other tarsomeres.

Onorius was described as monotypic with the only species, O. inexpectatus, found in the cloud forests in Cotopaxi Province, central Ecuador. Now we have examined a female from south-eastern Ecuador, a locality on the border with Peru. The specimen shares all the taxonomic characters of the genus Onorius yet has a strikingly different body sculpture and coloration, showing clearly that it is non-conspecific with the type species of the genus. Examination of the hind gut of the two species revealed additional character supporting generic rank of Onorius. The goal of the present contribution is to complete the diagnosis of the genus with the characters of the hind gut morphology and describe and illustrate the new species. However, we do not give the new species a formal name (see Discussion below).

Material and methods

The material used in this work is housed in the collection of Biosciences Institute, Federal University of Mato Grosso, Cuiabá, Brazil (CEMT, curator F.Z. Vaz-de-Mello). Morphological terminology follows Frolov et al. (2016). Specimens, digital images and locality maps preparation follow Frolov et al. (2017a).


Onorius Frolov & Vaz-de-Mello, 2015

Type species. Onorius inexpectatus Frolov & Vaz-de-Mello, 2015, by original designation.


Onorius sp.


Material examined. Female: “Zamora Chinchipe Paquisha Alto Marzo 2008 Col. V. Carvajal” (CEMT).


This species differs from O. inexpectatus in the sculpture of the body (Fig. 1 A): head is punctate with transversely elongate, sometimes adjoining punctures (punctures are round and relatively sparse in O. inexpectatus); pronotum with coarser ocellate punctures (punctures are smaller and not ocellate in O. inexpectatus); elytra with characteristic U- to V-shaped punctures each bearing a distinct yellowish seta posteriorly (punctures are round in O. inexpectatus; setae in the punctures are smaller, barely visible at the same magnification); proximal ileum has two large, symmetrical diverticula (Fig. 2 B).

Description. Female (Fig. 1, 2). Body length 9.0 mm, width of elytra 4.6 mm, width of pronotum 3.5 mm. Color uniform brown with pronounced bronze tint.

Head densely punctate with transversely elongate punctures; some punctures fused near anterior margin of clypeus. Head without traces of medial horn or tubercle. Left mandible slightly protruding past clypeus in dorsal view; labrum not protruding past clypeus. Clypeus rounded anteriorly.

Pronotum 1.5 times wider than long, widest at basal 0.3 of its length. Anterior margin without border, basal and lateral margins bordered. Disc with shallow impression anteriorly and near base, without tubercles or deep fossae. Surface punctate with round ocellate punctures separated by 1–3 puncture diameters.

Scutellum triangular, narrowly rounded apically, about 1/15 length of elytra, coarsely punctate.

Aegidiini. Onorius sp.¸ Ecuador, Zamora-Chinchipe, Paquisha, Alto Marzo
Figure 1. Aegidiini. Onorius sp.¸ Ecuador, Zamora-Chinchipe, Paquisha, Alto Marzo (A–C, F), O. inexpectatus (D, F), Aegidium onorei (E). Habitus in dorsal (A) and ventral (B) view, external female genitalia in ventral view (C–E), locality map (F; dot — O. inexpectatus, triangle — O. sp.).

Elytra convex, with marked humeral and apical humps, without ridges or other elevated areas. Maximum width approximately at the middle. Striae indistinct. Elytra punctate with U- or V-shaped punctures; each puncture bears a short, yellow seta posteriorly. Base of elytra not bordered.

Wings fully developed.

Protibiae with 3 outer teeth, without smaller inner tooth. Lateral margin basad of outer teeth not crenulate. Apex and internal margin of tibia with a few slender setae. Protarsi well developed, about 2/3 length of protibiae. Claws 1/3 length of tarsomere 5. Tarsomere 5 as long as tarsomeres 2–4 combined. Tarsomere 1 as long as tarsomeres 2–4.

Hind and middle legs similar in shape; metafemora and metatibiae about 1.2 times longer than mesofemora and mesotibiae. Femora sparsely punctate with elongate punctures. Tibiae somewhat triangular, with 2 apical spurs. Upper tibial spur as long as tarsomeres 1–3; lower spur as long as or slightly longer than tarsomere 1. Claws 1/3 length of tarsomere 5. Tarsomere 5 relatively robust, as wide as the other tarsomeres, as long as tarsomeres 2–4 combined and as long as tarsomere 1.

Abdominal sternites punctate with elongate punctures. Sternite 8 about 2 times wider than sternites 4–7 medially.

Pygidium transverse, irregularly punctate, partly hidden under elytra.

Male unknown.

Distribution and habitat. The new species is known from only one locality, Alto Marzo in Zamora-Chinchipe province of Ecuador (Fig. 1 F), a place on the western side of the Cordillera del Cóndor, an elevated (over 2000m) enclave in the Amazonian hylaea that appears to present high endemicity. The exact habitat and collecting circumstances of the specimen are unknown. Considering the characters of the genus and complete absence of the soil contamination, normally found in all Aegidiini taxa except Onorius, we think that the new species is a canopy dweller similar to O. inexpectatus.


Although the species from Alto Marzo differs strikingly from O. inexpectatus and there is no doubt that it is new to science we do not give it a formal name. We cannot exclude the possibility that in the future, another or other closely related Onorius species will be discovered in Alto Marzo area and, in contrast to O. inexpectatus, these species may be indistinguishable by females. The characters of the females do not allow distinguishing closely related species in most Orphninae taxa (Paulian 1948, Frolov 2010, Frolov, Montreuil and Akhmetova 2016). The notable exception is Aegidinus Arrow which shows a large variation of the shape of the gonocoxites (Colby 2009, Frolov Akhmetova and Vaz-de-Mello 2019). However, in all other Aegidiini genera, females of the closely related species are difficult to impossible to distinguish (Frolov et al. 2017b, Frolov et al. 2017c, Frolov, Akhmetova and Vaz-de-Mello 2017a). Females of congeners may differ externally (but not necessarily in the shape of the genitalia; e.g. both known Onorius species have similar female genitalia [Figs. 1 C, D] similar also to Aegidium [Fig. 1 E]) as in some Orphnus, Aegidium and other genera but these differences are normally associated with much higher differences in the male characters and indicate that the species belong to different species-groups or subgenera.

Every reasonable attempt was made to obtain additional specimens, including males, to complete the formal description of the species from Alto Marzo. All available collections were checked and we specifically asked the colleagues from Ecuador and Peru for additional material. A dedicated expedition to the area is difficult logistically and would require a work in the canopy that further complicates the sampling of Onorius and makes it practically unfeasible for the authors. However, we hope that this publication will attract the attention of the scientists and collectors working in the area and eventually the additional material will be collected to allow to complete the description of the species.

Unfortunately the specimen we examined was treated with KOH making extraction of DNA for further association with males by the molecular methods (e.g. DNA barcode) likely impossible. However, despite the DNA barcode would contribute to the diagnosis of the species, we think that it would not make the naming more appropriate in this case because the DNA barcode method has limitations and is not 100 per cent accurate.

Both known species of Onorius were found to have two characteristic, symmetrical ileum diverticula (Figs. 2 A, B, arrowed). Comparative study of the hind gut morphology of all Orphninae taxa is outside the scope of the present contribution, but in the course of our revision of the Orphninae the hind gut was studied in a number of taxa. This study showed that the Onorius type of ileum is not found in the other orphnines. In the Aegidiini genera Aegidium and Paraegidium, the proximal ileum is similar and has a few subsymmetrically situated protuberances rather than longer diverticula (Fig. 2 E–G). The exact number of the protuberances is difficult to estimate, at least in the dry collection material available to us. In the Madagascan genus Triodontus, the shape of the ileum varies between the two species examined from four well-developed, rather long diverticula in T. nitidulus (Fig. 2 D) to the complete absence of diverticula and protuberances in T. itremoi (Fig. 2 C). The development of the ileum diverticula most probably reflects the feeding habits of the taxa, and yet data about the later in orphnines is mostly absent.

Morphology of the digestive system in general and hind gut in particular is poorly studied in the Scarabaeoidea. Few papers deal with comparative morphology of the alimentary channel and its phylogenetic implementation (Umeya 1960, Umeya 1974, Lopez-Guerrero 2002, da Fonseca et al. 2011), yet these studies show a reasonable diversity of the morphological structures and the possibility to address both physiological and evolutionary questions in scarabs. Feeding habits are practically unknown in the Orphninae, but the well-developed ileum diverticula, similar to the Passalidae genera Aulacocyclus Kaup and Ceracupes Kaup (da Fonseca, Fernandez and Barbosa 2011), may suggest xylophagy in adult Onorius, which requires large fermentation chambers.

Figure 2. Orphninae, hind gut. Onorius inexpectatus Triodontus itremoi Paraegidium howdeni Aegidium asperatum Paraegidium pokornyi Ileum diverticula and protuberances


Figure 2. Orphninae, hind gut. Onorius inexpectatus (A), O. sp., Ecuador, Zamora-Chinchipe, Paquisha, Alto Marzo (B), Triodontus itremoi (C), T. nitidulus (D), Paraegidium howdeni (E), Aegidium asperatum (F), Paraegidium pokornyi (G). Ileum diverticula and protuberances in the Onorius are arrowed.


Lic. Vladimir Carvajal (Escuela Politécnica Nacional, Quito, Ecuador) very kindly presented the examined specimen to FVM. We are thankful to Frank Krell (Denver Museum of Nature & Science, Denver, U.S.A.) and three anonymous reviewers for the comments on the early version of the manuscript. This work was supported by the National Council for Scientific and Technological Development of the Ministry of Science, Technology, and Innovation of Brazil, CNPq (405697/2013-9, 440604/2015-0, 400681/2014-5, 306745/2016-0) and partly by the Russian Foundation for Basic Research (grant number 16-04-00412-a). The study was completed in the framework of the Russian state research project АААА-А19-119020690101-6.



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