Ana Helena Cruciol, Fernando Barbosa Noll, Rogério Botion Lopes
Zethus Fabricius is the largest genus of vespid wasps with over 300 species worldwide that are divided into subgenera and further into species groups. Recent phylogenetic studies raised the number of subgenera from four to nine, six of which are in the Neotropics. However, three Neotropical species groups were not assigned to any subgenus due to lack of node support. The Zethus spinosus species group is such a case and, while previously inserted in the nominotypical subgenus, it was recovered closer to Zethus (Zethusculus), but with no support. Thus, a phylogenetic parsimony analysis of morphological data of the group was carried out with better ingroup and outgroup sampling for testing to find a more robust resolution for the group's placement. We recovered the Zethus spinosus group as monophyletic and as a sister group of Zethus (Zethusculus). In both cases, it was not only unique synapomorphies that supported the clades, but symmetric resampling also recovered significantly better values. Therefore, to maintain all taxa monophyletic, a new subgenus, "Zethus (Zethittus)" Cruciol & Lopes, subg. n., is described to accommodate the Zethus spinosus group. Additionally, a new species, Zethus (Zethittus) ramphoceros Cruciol & Lopes, sp. nov. from Brazil is described herein. The present study also provides a new record of Zethus semiplanus Cruciol et al. (2026).