Taxonomic revision of boreus species group of Dichotomius Hope, 1838 (Coleoptera: Scarabaeidae: Scarabaeinae: Dichotomiini), with a description of two new species from western Amazon

Dung beetles play a crucial role in ecosystem functioning, particularly in the Neotropical regions. The boreus species group of the genus Dichotomius includes typical large tunneler species that often possess complex armatures on the head and pronotum. In this study, we recognize seven species within this group, mostly recorded in the Amazon region: Dichotomius boreus (Olivier, 1789), Dichotomius pelamon (Harold, 1869), Dichotomius podalirius (Felsche, 1901), Dichotomius prietoi (Martinez and Martinez, 1981), Dichotomius quadrilobatus (Chamorro, Lopera-Toro & Rossini, 2021), Dichotomius uacari sp. n., and Dichotomius divisor sp. n. Lectotypes are designated for D. boreus, D. pelamon, D. podalirius, and Dichotomius carinatus. A new subjective synonymy is established D. carinatus = D. pelamon. This work provides a detailed literature review, an updated identification key, descriptions, diagnoses, a list of examined material, and geographic data for each species.