Onthophagus mirabilis Bates, 1887

Génier, François & Medina U, Claudia A., 2004, Onthophagus mirabilis Bates, Description of the Newly Discovered Female (Coleoptera: Scarabaeidae, Scarabaeinae), The Coleopterists Bulletin 58 (4), pp. 610-612 : 610-612

Onthophagus mirabilis Bates, 1887

Description. Female. Length 8.3–12.1 mm, greatest width 4.4–6.3 mm. Color. Dark reddish brown except for light reddish brown femora. Head. Anterior edge of clypeus ( Fig. 1 ) distinctly bidentate, median emargination broadly V-shaped; teeth reflexed, lateral edges of teeth nearly parallel in larger individuals; clypeal edge, on each side, slightly outwardly arcuate, sharp, lacking distinct marginal bead; clypeal surface flat, rather coarsely punctate, punctures dense and forming more or less distinct transverse wrinkles laterally in some individuals, surface shiny between punctures; clypeal carina wide, sharp and slightly tri-sinuate, reaching clypeogenal suture laterally. Gena with surface flat and shiny, punctures smaller and ill-defined throughout, with lateral edge narrowly rounded posterior to clypeogenal suture, straight medially, widest portion forming blunt angle. Vertex ( Fig. 1 ) with surface variably punctate throughout, punctures varying from coarse to ill-defined, surface slightly convex, with high transverse carina medially, lateral extremities of carina produced into conical horn, each horn pointing slightly laterally and in line with median portion of eye, lateral edges of carina on each side approximately on lateral third of distance between eyes, frontal carina reduced in height and lacking lateral horns in feebly developed individuals. Pronotum ( Fig. 1 ). Anterior marginal bead unmodified. Anterior portion medially with a strong projecting transverse tubercle, tubercle reduced in feebly developed individuals; disc longitudinally concave at midline on anterior half, concavity bordered by projecting triangular

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carinae laterally, concavity barely indicated and carinae reduced to small tubercles in most feebly developed individuals, concavity never bordered by a tubercle posteriorly; pronotal surface coarsely and densely punctate except in median concave area of large individuals. Elytra. Striae clearly defined throughout, punctures of striae well impressed and encroaching on intervals; surface of intervals with punctures deep and confluent, producing a more or less irregular pattern.

Legs. Fore tibia not elongate, lacking tooth and tuft of setae apically; femur with ventral surface minutely punctate, surface between punctures with feeble microsculpture. Metasternum. Median lobe with accessorial long and erect setae anterolaterally.

Material Studied. 3 ##, 8 $$ (Canadian Museum of Nature, Claudia Medina collection) Colombia: Valle del Cauca: R[eserva]. F[orestal]. Bosque de Yotoco, 1,600 m, Junio 19 1999, Claudia A. Medina, fruto ficus (1 #, 3 $$); same data except: Mayo 25 1997, T[rampa]. Fruta (1 $); Junio 1999, T[rampa]. caida (1 #, 1 $); Junio 9 1999, T[rampa]. Interc[eption]. (1 #); 1,575 m, 23.VI.1999, William P. Mackay, pitfall trap (3 $$).

Remarks. The strongly concave pronotum with a strong median projection anteriorly (in larger individuals) suggest that this species is most closely related to O. orphnoides Bates. The females belonging to other species of the group have either a simply convex, or slightly depressed pronotum anteriorly ( O. solisi Howden and Gill ), a simply convex pronotum with a transverse carina ( O. barretti Génier and Howden ), or the anterior portion is flat and bordered posteriorly by a tubercle ( O. breviconus Génier and Howden , O. neomirabilis Howden ).

Female specimens will key out as O. orphnoides Bates (couplet 7(1 9 )) in Génier and Howden (1999). However, specimens can easily be separated from O. orphnoides by the presence of a strong and laterally tuberculate transverse carina on the vertex and coarse and sharply defined pronotal punctures.

To determine if characters of the female O. mirabilis agreed with the phylogenetic hypothesis presented in Génier and Howden 1999, the data matrix was analyzed again with the previously unknown characters included. The addition of the female of O. mirabilis did not change the most parsimonious tree previously obtained.

Biology. Onthophagus mirabilis is now known from one locality in Ecuador and one locality in Colombia ( Valle del Cauca ). The site in Colombia is located in a humid 612 tropical montane forests, at an elevation between 1,575–1,600 m. Colombian specimens were almost exclusively caught using unbaited or rotten fruit baited pitfall traps. Only one specimen each was collected by using flight intercept, human dung baited pitfall, or rotten egg baited pitfall traps. We suspect that these instances were essentially random, equivalent to un-baited pitfall traps. In the Reserva Forestal de Yotoco, rotten fruit traps (a mix of banana, orange, guava, and mango) were set in June 1999. Other traps were baited with rotten fruits found locally on the forest floor, and others with fungi. However, no specimens of O. mirabilis were attracted to traps baited with fungi. Onthophagus mirabilis was collected with only one other species of Scarabaeinae (Ateuchus sp.) in traps with mixed fruit, and in traps baited with figs (Ficus sp., Moraceae).

The Reserva Forestal de Yotoco consists of 559 hectares of forest surrounded by a mosaic of pastures and plantations, mainly coffee and green bananas (platano). It is located 50 km northwest of Cali on the East slope of the Cordillera Occidental of the Colombian Andes. Although traps were also set in plantations and pastures around the forest, the species was not caught there (C.A. Medina, unpubl. data). The reproductive behavior of Onthophagus mirabilis remains unknown, but their unambiguous preference for fruit baited traps suggest that, as with other species in the group, they utilize fruit as a food source as adults and possibly for their larval development. Unfortunately, we believe that O. mirabilis is at risk in Colombia as its distribution seems restricted to mid-elevation undisturbed forest, a habitat that is greatly threatened in the region.

Figures

Fig. 1. Habitus, Onthophagus mirabilis Bates, well-developed female (note: front tarsi missing). Total length ¼ 12.1 mm.