Phylogenetic analysis of the genera of endemic Hawaiian sap beetles (Coleoptera: Nitidulidae) based on morphology with redescription and key to the genera of endemic Hawaiian Nitidulidae
The endemic Hawaiian sap beetles were originally placed in 13 genera in 1908; Apetasimus, Apetinus, Cillaeopeplus, Cyrtostolus, Eunitidula, Eupetinus, Gonioryctus, Goniothorax, Nesapterus, Nesopeplus, Nesopetinus, Notopeplus, and Orthostolus. Apetasimus, Cyrtostolus, Eunitidula, and Notopeplus were described for single species, with additional species later described for Apetasimus and three undescribed species known for Eunitidula from Oahu, Molokai, and West Maui. Nesopeplus and Nesopetinus have been previously shown to be junior synonyms of Prosopeus. The monophyly of the genera is tested using morphological characters, primarily of the male copulatory sac, in a parsimony framework. The results provide the rationale for reducing the number of endemic genera to six; Apetasimus (= Cyrtostolus + Orthostolus in part), Cillaeopeplus (= Notopeplus), Eupetinus (= Apetinus), Gonioryctus (= Eunitidula + Goniothorax + Nesapterus), Orthostolus s.s., and Prosopeus. Brachypeplus (= Cillaeopeplus) gracilis, a species endemic to Guam, was placed in the formerly Hawaiian endemic Cillaeopeplus in 1962. Examination of the types of all species of Cillaeopeplus shows no direct connection between B. gracilis and the Hawaiian taxa comprising the remainder of Cillaeopeplus. Brachypeplus gracilis is placed incertae sedis in Brachypeplus herein. The position of the endemic Hawaiian sap beetles within the nit idulid subfamily Cillaeinae is surveyed using exemplar species from 22 of 27 genera placed in Cillaeinae. Undescribed species from eastern Polynesia allied with Brachypeplus subgenus Selis are proposed as the closest relatives of the Hawaiian endemic sap beetles based on internal and external morphology.