Orizabus ligyroides Horn, 1885

Warner, William B., 2011, Review of the genus Orizabus Fairmaire in the United States of America (Coleoptera: Scarabaeidae: Dynastinae), Insecta Mundi 2011 (174), pp. 1-42 : 6-7

Orizabus ligyroides Horn

Fig. 3, 4 , 27, 29 , 38 ; Map 2

Orizabus ligyroides Horn 1885:125 , Ratcliffe and Cave 2010:1. Type. Holotype female (MCZC #3705); type locality: “...collected by Mr. Morrison in Arizona ”.

Diagnosis. Length 19.0 to 27.5 mm, width at humeri 9.0 to 12.5 mm, widest width 11.0 to 16.0 mm. Large for genus, parallel sided to wider behind but not distinctly pyriform. Clypeus subtriangular, with apex narrowly rounded; clypeal carina apparently apical, distinctly bidentate, teeth rounded, contiguous such that carina appears medially cleft ( Fig. 3 , 38 ). Maximum dorsal eye width usually between 1/3 and 1/4 of minimum dorsal interocular width. Pronotum with posterior marginal bead distinct (in all US specimens examined). Male with dorsal margin of protibia edentate, bladelike; pronotum anteromedially with perceptible to large depressed area, anterior marginal bead posterodorsally prolonged at midline into conical tubercle; paramera without apical incisure, essentially identical to those of O. clunalis , but with lateral subapical “tooth” (a short carina) usually less evident, and apex usually more oblique ( Fig. 27, 29 ).

Female with dorsal margin of protibia tridentate, its apex oblique; pronotum with posterior margin of anterior marginal bead subangularly broadened or forming tubercle as in male, disc without or with weak anteromedial depressed area.

US Distribution. AZ, NM, southwestern KS, western TX. The New Mexico, Texas, and Kansas localities are all new state records.

Specimens Examined. 1135; see appendix for locality data.

Remarks. Bates (1888) apparently synonymized O. ligyroides as the female of O. clunalis , a status that has been carried on by all subsequent authors until Ratcliffe and Cave (2010) recently resurrected O. ligyroides without comment. In fact, the type specimens of both species are females. Orizabus ligyroides inhabits desert grassland, prairie, and oak and juniper woodland habitats at elevations between about 1000 and 1800 m. In intermediate elevations (oak and juniper woodland) it may be taken at light along with O. clunalis which it resembles in size and genital form. It may immediately be differentiated from that species, however, by its thicker (in lateral Table 1. Habitat preferences of O. ligyroides and O. view), subtriangular (in dorsal view) clypeus and clunalis illustrated by comparing locality records from apparently apical clypeal carina with contiguous the Cave Creek drainage in the Chiricahua Mountains, teeth (compare Fig. 1-4 , 36-38 ). Arizona.

The different habitat preferences of O.

ligyroides and O. clunalis are illustrated by com-

paring locality records for both species from the

Cave Creek drainage in the Chiricahua Mountains,

Arizona. The proportion of specimens collected from

the vicinity of Portal at the canyon’s mouth, ver-

sus the proportion of specimens collected near or above the AMNH Southwestern Research Station five miles up the canyon, is essentially reversed for the two species (Table 1). Collecting bias between the species is not a factor as the adults are of similar size and color, and had not been recognized as distinct since Bates’ (1888) synonymy. Portal is at the ecotone between mesquite-creosote bush grassland that surrounds the mountains and oak-juniper woodland which begins at the mountain base and is replaced by pine forest at higher elevations. The Southwestern Research Station is located in mixed juniper-oakpine association. Orizabus ligyroides also occurs in the desert grasslands below Portal; however, the grasslands are relatively poorly collected. Portal O. clunalis records may result from beetles flying downhill from more montane locations; high elevation habitats are only a short distance “as the crow flies” from lowland habitats because of the mountain’s steep grade. Or, these records may represent O. clunalis following the cooler riparian habitat of Cave Creek to a lower elevation; Portal is also essentially the end of the dense broadleaf canopy that occurs along the more montane portions of the creek.

Given the differences in clypeal shape and habitat type from that of O. clunalis , O. ligyroides adults probably do not feed on coniferous plants. Common plants where most O. ligyroides have been found include grasses, mesquite ( Prosopis sp. ), juniper ( Juniperus sp. ) and oaks ( Quercus sp. ).

Interestingly, the O. pyriformis-O. mcclevei pair is analogous to the O. ligyroides-O. clunalis pair, with the grassland species ( O. pyriformis ) having a more angular clypeus with apical carina, and the more montane O. mcclevei having a parabolic clypeus with subapical carina. Perhaps the narrowed clypeus and apparently apical carina is an adaptation for feeding on grasses.

Figures

Figure 36. Orizabus clunalis: Anterolateral view of male (Texas) head and pronotum.

Figures 37-38. Dorsal view of female head and anterior pronotum: 37) O. clunalis (Arizona), 38) O. ligyroides.

Figures 1-4. Dorsal and right lateral views of head and anterior third of pronotum: 1-2) O. clunalis. 3-4) O. ligyroides.

Figures 26-31. Dorsal and lateral views of paramera: 26, 28) O. clunalis. 27, 29) O. ligyroides. 30) O. pinalicus holotype. 31) O. rubricollis.