Deuterodiscoelius Dalla Torre and Pachycoelius Giordani Soika are two small genera of Australian vespid wasps. While the first came from the splitting of Discoelius, the latter was created to accommodate species with a few distinct traits, some of which were not observable due to the absence of male specimens of two out of the three species designated to the genus. This already blurry delimitation of the genera was heightened when specimens of an unknown species presented a combination of characters from both genera. Hence, to properly assign this species to a genus, a phylogenetic study based on morphology was carried out before the species description. The analysis recovered both genera as unnatural, resulting in the synonymy of Pachycoelius under Deuterodiscoelius, and the new species, namely, Deuterodiscoelius delator Lopes and Carpenter, new species, was subsequently described.