Dichotomiini Pereira, 1954

Montoya-Molina, Santiago & Vaz-De, Fernando Z., 2021, Taxonomic review of the Dichotomius (Luederwaldtinia) agenor species group (Coleoptera: Scarabaeidae: Scarabaeinae), European Journal of Taxonomy 734, pp. 1-64 : 4-5

Tribe Dichotomiini Pereira, 1954

Diagnosis of the Dichotomius (Luederwaldtinia) agenor species group

Within the subgenus Luederwaldtinia Martínez, 1951 , the Dichotomius agenor species group defined by Nunes & Vaz-de-Mello (2013) can easily be separated from other species groups by the following morphological characters: head of males bearing a transverse trituberculate carina, medial tubercle higher than lateral ones; in females head carina generally bituberculate or quadrituberculate, except in two species ( D. fornicatus and Dichotomius rafanunezi sp. nov.) where they are trituberculate; pronotum without ornamentation, displaying at most a truncate declivity or knob; pronotum convex in females.

Redescription

Large to medium-sized species (length: 11–28 mm). Body in most cases shiny black to brownish, rarely copper coloured (as in D. subaeneus ), dark blue (as in D. fornicatus ) or dull green (as in Dichotomius rafanunezi sp. nov.).

HEAD. Wider than long, anterior clypeal margin emarginate (V-shaped when seen from above), producing short, rounded, subtriangular clypeal teeth, in some species clypeal teeth acute (as in D. inachoides ) or reduced (as in D. belus ). Male head process (over the front-clypeal suture) consisting of transverse trituberculate carina (here referred to as the cephalic carina), medial tubercle clearly higher than lateral ones ( Fig. 1 A–D) or very slightly higher (as in D. subaeneus ). Clypeo-genal suture distinct and clypeogenal junction feebly emarginate. Genal border roundly expanded or even lobed posterior to clypeogenal suture.

PRONOTUM. Generally presenting a truncate slope or declivity on anterior portion, except for D. subaeneus which is convex. Hypomeral medial disc smooth ( Fig. 2E as in amplicollis ) or punctate ( Fig. 2F as in D. tristis ), lateral margins displaying single or multiple rows of long setae.

ABDOMEN. Metepisternum covered by ocellate setigerous punctures, upper posterior margin with subtriangular projection reaching the pseudoepipleuron. Metasternal medial disc smooth, lateral edges with dense pilosity (as in D. inachoides , D. deyrollei , D. validipilosus and D. simplicicornis ) or dispersed pilosity (as in D. belus and D. subaeneus ). Anterior portion near meso- and metasternal suture punctate, covered by long setae or not. Medial edges of sternites shiny, smooth or with single row of punctures; lateral portions exhibiting dense ocellate punctures. Male sixth sternite narrowed medially.

LEGS. Metacoxa displaying single (as in D. agenor ) or two rows of setae. Protibia calcar generally spiniform except apically bifurcate in D. belus and D. subaeneus .

SEXUAL DIMORPHISM. Smaller or less developed males of D. agenor species group have cephalic carina less developed or, as in females, bearing two tubercles. Females have larger clypeal teeth with deeper emargination, denser and longer pilosity, pronotal disc bearing deeper and denser punctures. Female

cephalic carina bi- or quadrituberculate ( Fig. 1 E–F), except for D. fornicatus and D. rafanunezi sp. nov., in which is trituberculate. Female sixth abdominal sternite twice as wide in the middle as in males and not narrowed medially.

Distribution

The distribution of the Dichotomius (L.) agenor species group is broad, from the north Pacific coast of Mexico (Sonora desert) to the central region of South America ( Argentina: Santiago del Estero, Brazil: Mato Grosso state). Altitudinal range is variable, from nearly 3000 metres in the Andes mountain range to sea-level at the Atlantic or Pacific coast.

Figures

Fig. 1. Diagnostic characters of the Dichotomius (Luederwaldtinia) agenor species group. A–D. Male diverse trituberculate fronto-clypeal carina shapes. A. D. tristis (Luederwaldt, 1923). B. D. amplicollis (Harold, 1869). C. D. belus (Harold, 1880). D. D. validipilosus (Luederwaldt, 1931). E–F. Female fronto-clypeal carina. E. Bituberculate carina typical of D. tristis. F. Quadrituberculate carina typical of D. amplicollis.

Fig. 2. General characters that help differentiate the species of the Dichotomius (Luederwaldtinia) agenor species group. A–D. Ventral clypeal process. A. Cordate as in D. agenor (Harold, 1869). B. Truncate as in D. sagittarius (Harold, 1869) stat. rev. C. Bifurcate as in D. belus (Harold, 1880). D. Cylindrical as in D. henripittieri sp. nov. E–F. Hypomeral characters. E. Medial disc smooth, lateral margin with multiple rows of setae as in D. amplicollis (Harold, 1869). F. Medial disc punctate, lateral margin with single row of setae as in D. tristis (Luederwaldt, 1923). G–H. Metasternum characters. G. Setigerous punctures from the medial and lateral edges joining throughout the margin of the mesocaxa as in D. enioi sp. nov. H. Setigerous punctures from the medial and lateral edges not joining throughout the margin of the mesocaxa as in D. centralis (Harold, 1869). I–J. Elytra interstriae. I. Smooth as in D. amplicollis. J. Shagreened as in D. agenor.