Onthophagus brevifrons Horn, 1881

Edmonds, W. D., 2018, The dung beetle fauna of the Big Bend region of Texas (Coleoptera: Scarabaeidae: Scarabaeinae), Insecta Mundi 642, pp. 1-30 : 12

Onthophagus brevifrons Horn

Fig. 36–40

Diagnosis. Weakly shining black, often with bluish or greenish reflections. Length 7–10 mm. Pronotum ( Fig. 40 ) bearing sharply defined, sometimes setose, deep punctures interspersed with much smaller, shallower punctures, puncturing densest on anterior face and disk. Front legs similar in both sexes, not elongate in male ( Fig. 39 ). Elytral interstriae tuberculate. Male ( Fig. 36–37 ) – Clypeus reflexed, anterior edge truncate, transverse carina absent or only weakly indicated; frontal carina with median tubercle; pronotum strongly humped anteriorly, hump rounded (seen from above), presenting a near-vertical, bilaterally weakly concave anterior surface. Female ( Fig. 38 ) – Clypeus rounded, scarcely reflexed, clypeal carina strong, raised medially; frontal carina strongly developed, extending between eyes; pronotum convex, broadly tumid anteriorly, but never as strongly as in male. This species was re-described by Howden and Cartwright (1963).

Big Bend collection sites (altitudinal range: 1410–1785 m).

Presidio Co.: [1] Pinto Canyon Ranch (~ 58 km SSW Marfa on FM 2810), 30°01′18″N 104°27′42″W (headquarters area), 1475 m (Aug) ; [2] C.E. Miller Ranch (~ 16 km W Valentine), 30°32′50″N 104°39′40″W ( Camp Holland) 1410 m (Aug) .

Jeff Davis Co.: [1] * Davis Mountains Preserve, 31°37′42″N 104°05′01″W, 1785 m (May) .

Collection method(s). a) baited pitfall trap (human feces); b) direct capture on ground surface; (c) soil beneath Neotoma nest.

Surface activity. Presumed nocturnal.

Habitat. All zones in association with wood rats ( Neotoma ).

Comments. Onthophagus brevifrons is the scarcest and largest species of Big Bend Onthophagus , always collected in low numbers (one to four individuals in lethal pitfalls) in creek beds and arroyos where wood rats are known to occur. The low numbers undoubtedly reflect a strong preference for wood rat feces such that significant numbers are more likely to result by excavating the soil beneath the rodent′ s nest quarters. It is similar to O. coproides Horn , an inquiline in pocket gopher nests in Arizona, New Mexico and northern Mexico and to other species of mountainous Mexico with broadly humped male pronotum (the chevrolati group), many of which are associated with mammal nests. This species is one of a triplet of closely related US species, all with specialized microhabitats: O. brevifrons in wood rat nests; O. subtropicus Howden and Cartwright in wood rat nests of east Texas; and O. cavernicollis Howden and Cartwright with cave-dwelling bats in Arkansas ( Halffter and Matthews 1966). Slay et al. (2012) speculate that this latter species, while collected in bat guano, actually utilizes wood rat dung in the caves for breeding. Small males of O. brevifrons can closely resemble the female, from which they can be distinguished by having a medially emarginate last abdominal sternum (as in Fig. 27 ). Riley and Wolfe (2003) reported O. brevifrons also from south Texas and the Panhandle plains regions of the state. Cokendolpher and Polyak (1996) collected a specimen from Milliped Cave, Sinkhole Flat, Eddy Co., NM (~ 35 km NW Carlsbad ~ 3700 ft). Howden and Cartwright (1963) report collecting it along with O. browni from a single Neotoma nest in Portal, Arizona.

Figures

Figures 36–48. Onthophagus. 36) O. brevifrons, dorsal view, male. 37) Same, oblique frontal view. 38) Same, dorsal view of forebody, female. 39) Same, prolegs (A, female; B, male. 40) Same, pronotal sculpturing. 41) O. browni, dorsal view, male. 42) Same, oblique frontal view. 43) Same, oblique frontal view, female. 44) O. velutinus, dorsal view, male. 45) Same, oblique frontal view. 46) Same, dorsal view of female forebody. 47) Same, oblique frontal view. 48) Same, pronotal sculpturing.

Figures 26–35. Canthon. 26) C. imitator, dorsal view, male. 27) Same, ventral view of abdomen. 28) Same, ventral view of female abdomen. 29) C. blumei, dorsal view, female. 30) Same, oblique dorsal view of forebody. 31) Same, ventral view of right propleuron (arrow marks transverse carina). 32) C. imitator, ventral view of right propleuron. 33) C. mixtus, dorsal view, male. 34) C. praticola, dorsal view, female. 35) Same, oblique view.