Revisão taxonômica do subgênero Dichotomius (Dichotomius) Hope, 1838 (Coleoptera : Scarabaeidae : Scarabaeinae)

Abstract

Dichotomius Hope, 1838 is one of the most diverse and abundant genera of dung beetles (Scarabaeidae: Scarabaeinae) in the New World, with more of 200 species distributed from the northeastern United States to central Argentina. It has been divided into four subgenera: Dichotomius sensu stricto, Cephagonus Luederwaldt, 1929, Homocanthonides Luederwaldt, 1929 and Selenocopris Burmeister, 1846. The nominotypic subgenus showed the least progress in its taxonomy, with only 15% of the species having information in a recent revision. The objective of this work was to perform a taxonomic revision of Dichotomius s. str. using a traditional taxonomic revision protocol based on external and male genitalia morphology, with the review of the type material and more than 12,000 specimens from 32 entomological collections. In Chapter 1, we split the subgenus into two, creating the new subgenus Dichotomius (Luederwaldtius), which includes the smallest species (less than 20 mm), 13 species previously included in Dichotomius s. str., four species of Dichotomius (Selenocopris), and several undescribed species. Dichotomius triangulariceps (Blanchard, 1846) was transferred to the subgenera Selenocopris. The subgenus Dichotomius s. str. in its new, narrower sense, is delimited to include about 73 species, organized in 12 groups, and two incertae sedis species. For each species group, we present its definition, species composition, and geographic distribution. The species incertae sedis, D. agesilaus (Waterhouse, 1891) and D. compressicollis (Luederwaldt, 1929) are reviewed. In following chapters, taxonomic revisions of some of the delimited groups are made. In chapter 2, the Dichotomius cotopaxi (Guérin-Méneville, 1855) species group has been revised, with five species belonging to this group, including two new species, one from Colombia and the other from Ecuador. In chapter 3, the Dichotomius mormon (Ljungh, 1799) species group has been revised, with five species included, one of which is a new species from Bolivia. In chapter 4, the Dichotomius bitiensis (Gillet, 1911) species group was revised, with six species included, one of which is new from Colombia. Finally, in chapter 5, a taxonomic revision of the Dichotomius depressicollis (Harold, 1867) species group was performed, including eight species, five of which are new, one from Bolivia, three from Brazil and one from Peru. With the results presented here, the revision of the subgenus reaches 50% progress, and the remaining groups and the new subgenus already under review.