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Two New Species of the Onthophagus clypeatus Species Group (Coleoptera: Scarabaeidae: Scarabaeinae)

Abstract Two new species of Onthophagus from Oaxaca, Mexico, are described and illustrated: Onthophagus istmenus new species, and Onthophagus santamariensis new species. Keys for separating major males of the new and allied species are presented. Taxonomic remarks are commented for the new and closely related species.

New World Onthophagus Latreille are divided into supraspecific units, considered as species groups and complexes. Howden & Gill (1993) defined the Onthophagus dicranius and the Onthophagus mirabilis (both Coleoptera: Scarabaeidae) species groups to include some Mesoamerican species. Zunino & Halffter (1997) proposed the Onthophagus clypeatus (Coleoptera: Scarabaeidae) species group, with 28 species distributed from Mexico to South America, including those of the species groups defined by Howden & Gill (1993). Génier & Howden (1999) redefined the O. mirabilis and O. dicranius species groups, but Kohlmann & Solís (2001) merged the species of both groups into the O. dicranius species group. The structure of the O. dicranius species group was redefined by Génier (2017), who split it into the O. dicranius and O. mirabilis species complexes. In this context, we accept the grouping of the O. clypeatus and the O. dicranius species groups. This study aims to describe 2 new species of the O. clypeatus species group. Keys for separating the major males of the new and closely related species are presented. We also comment upon the relevance for systematics of the discovery of these new species.

Material and Methods
Abbreviations for collections cited in this work are as follows: CEMT (2000), which defines the species as the smallest aggregation of populations or lineages that is diagnosable by a unique combination of character states. Type specimens bear determination labels printed on red acid-free paper, indicating specimen sex, and which one is holotype and which are paratypes. A second label printed on white acid-free paper contains the collection data. Label data is given verbatim. Genital structures were prepared with a 10% KOH solution, soaked 24 h at room temperature, rinsed with 96% ethanol, then with water, and stored in microvials (BioQuip Products, Inc., Rancho Dominguez, California, USA) with glycerol. These microvials were pinned under the dissected specimens. Measurements and pictures were taken with a Leica Z16APOA stereomicroscope (Leica Microsystems, Wetzlar, Germany) using the manufacturer's software (z-stack image capture method). Climate data was taken from INEGI (2019).

ETYMOLOGY
The specific epithet derives from "Istmeño," the demonym for inhabitants of the Tehuantepec Isthmus, Oaxaca, Mexico.

MALE
Holotype major male (Fig. 1a). Length 8.5 mm, pronotal width 4.3 mm, elytral width 4.6 mm. Dorsal surface dark-metallic green in color with a reddish cast, glabrous, reticulate microsculpture. Head: hexagonal shape. Clypeal projection trapezoidal and bent upwards in frontal view, broadly bifurcate and u-shaped in dorsal view. Clypeal punctures weakly marked. Frons concave with weakly marked and irregularly sized punctures. Clypeal and frontal carinae lacking. Clypeogenal sutures well marked. Genae obtusely oval with large, coarse punctures. Two strongly elongate, inwardly curved, slender cephalic horns behind the eyes. Pronotum: lacking projections. Anterior midline not marked. Anterior half of pronotum with 2 concavities. Weakly marked, minute, sparse punctures in the anterior-central portion of the pronotal disc; becoming ocellate, large and dense in the rest of the pronotum. Lateral fovea inconspicuous, irregular in shape. Elytra: dark matte-green in color. Elytral striae well marked, with well defined, variably sized and regularly spaced punctures. Interstriae with minute punctures. Pygidium: coarse, confluent, dense punctures, becoming smaller and less dense towards the apex. Setae sparse. Protibia: quadridentate on external border, lacking projections on internal border and apex. Apex with a long setal brush (some setae are lost by abrasion). Parameres: apical teeth acute, well developed (Fig. 1c). Lamella copulatrix: inferior right lobe much longer than the left lobe (Fig. 1d).

MINOR MALE
Differs from the major male by the parabolic clypeal apex, cephalic horns reduced to small conical tubercles, pronotum with 2 small pro-tuberances on the anterior half, pronotal punctures uniform in shape and size, and widened protibia. FEMALE Differs from the male by the head pentagonal in shape, bidentate clypeus, well-marked clypeal carina, small, straight cephalic horns, projected upwards and placed in the center of the frons, 2 small tubercles in the anterior half of the pronotum (Fig. 1b). The ventral portion of the vagina is well sclerotized (Fig. 1e).

DISTRIBUTION AND ECOLOGY
Onthophagus istmenus was collected in the Mountain Cloud Forest and the Tropical Rainforest between an elevation range of 150 to 1,700 m, a mean temperature of 16 to 26 °C, and an annual rainfall of 1,500 to 3,000 mm, from the Tehuantepec Isthmus, eastern Oaxaca, Mexico (Fig. 2). The new species follows the Typical Neotropical distributional pattern (Halffter & Morrone 2017), and may occur in Veracruz and Chiapas. Onthophagus istmenus was attracted to and captured with pitfall traps baited with human dung. Pereira & Halffter (1961) collected this species on horse dung. Species in the Onthophagus belorhinus Bates (Coleoptera: Scarabaeidae) species complex are frequently attracted to dung, carrion, and rotten fruits (Howden & Young 1981;Kohlmann & Solís 2001;Halffter & Halffter 2009).

DIAGNOSIS
Onthophagus belorhinus and O. istmenus seem to be closely related species. The major males of the new species can be distinguished easily by the obsolete anterior midline of the pronotum, whereas the midline in O. belorhinus is strongly impressed. The minor males and females can be confused, but both species differ in dorsal coloring (dark metallic green with a reddish cast or dark metallic red in O. istmenus; dark brown, brownish black, glossy with a cupreous cast in O. belorhinus) and elytral interstrial punctures (coarsely marked in O. istmenus, obsolete in O. belorhinus).

REMARKS
The O. belorhinus species complex was defined by Howden & Gill (1987) Kohlmann & Solís (Coleoptera: Scarabaeidae) are proposed by us in a preliminary manner to conform the O. belorhinus species complex. The major males of these species share the trapezoidal clypeal horn that is bent upwards in frontal view, with a u-shaped apical bifurcation; elongate, inwardly curved, slender cephalic horns rising behind the eyes; clypeal and frontal carinas absent; pronotum lacking well developed tubercles and projections, and occasionally with the midline strongly impressed in the frontal portion. Pereira & Halffter (1961)

ETYMOLOGY
The specific epithet derives from Santa María Chimalapa, the municipality where the type series was collected.

FEMALE
Differs from male by the head pentagonal in shape, clypeus reflexed and weakly sinuate, clypeal carina well marked, frons with 2 rounded transversal tubercles, pronotum uniformly punctate with coarse and ocellate punctures, anterior margin of pronotum with 2 almost indistinct concavities, and last abdominal sternite widened (Fig. 3b). The ventral portion of the vagina is well sclerotized (Fig. 3e).

DISTRIBUTION AND ECOLOGY
Onthophagus santamariensis was collected in Subtropical Oak Forest fragments surrounded by pastures, and Tropical and Subtropical Rainforests between an elevation range of 100 to 400 m, a mean temperature of 22 to 24 °C, and an annual rainfall of 1,500 to 3,000 mm, from Los Chimalapas region, eastern Oaxaca, Mexico (Fig. 2). The new species follows a Typical Neotropical distributional pattern (Halffter & Morrone 2017), and may occur in Veracruz and Chiapas. Onthophagus santamariensis was collected with pitfall traps baited with human dung. Species in the Onthophagus luismargaritorum Delgado (Coleoptera: Scarabaeidae) species complex are frequently attracted to dung and carrion (Delgado 1995;Delgado et al. 2006).

DIAGNOSIS
Onthophagus santamariensis and O. luismargaritorum seem to be closely related species. The new species may be distinguished easily by the acute longitudinal tubercles of the pronotum, separated by a shallow concavity in major males (rounded longitudinal tubercles, separated by a deep longitudinal concavity in major males of O. luismargaritorum), and the apex of parameres strongly projected anteriorly and obtusely triangular (dorsally concave, not strongly projected anteriorly, irregular in shape in O. luismargaritorum).

REMARKS
Onthophagus luismargaritorum, O. santamariensis, and Onthophagus yucatanus Delgado, Peraza & Deloya (Coleoptera: Scarabaeidae) share several characters that distinguish them from the remaining taxa of the O. clypeatus species group: the reduced size; clypeus obliquely reflexed and narrowly rounded; not strongly elongate, cephalic horns rising between the eyes; protibia short and wide; and female pronotum without tubercles (Delgado et al. 2006). These 3 species are proposed by us in a preliminary manner to conform to the O. luismargaritorum species complex.
Key to the species of the Onthophagus luismargaritorum species complex, based on major males