Potter wasps (Hymenoptera, Vespidae, Eumeninae) adopt different substrates for nesting, including other wasp nests. Nevertheless, such behavior rarely occurs with abandoned nests of the paper wasps (Hymenoptera, Vespidae, Polistinae). In this study, we report the occurrence involving the nesting of a potter wasp on a paper wasp’s nest. Such a record occurred in November 2021 in a segment of a deciduous forest, at Mata Seca State Park, Southeast Brazil. An abandoned Polistinae nest was found, with 14 cells sealed with mud, from which four male Pachodynerus nasidens individuals emerged. This record of P. nasidens reusing a Polistinae’s nest increases our knowledge of Eumeninae nesting strategies and on possible associations between different groups of vespid wasps.

A new Neotropical species of Pirhosigma Giordani Soika, 1978 is described, Pirhosigma transfluvium Ferreira & Oliveira. The male of Pirhosigma limpidum Giordani Soika, 1978 is reported for the first time. An illustrated identification key is presented for all currently recognized species of Pirhosigma.

A new species, Pirhosigma sulcata Ferreira & Hermes, sp. nov. is described from the Brazilian Amazon; the male of Pararhaphidoglossa gibbiventris Giordani Soika, 1978 is described for the first time. Pseudodynerus carpenteri Hermes & Melo, 2008 is newly recorded from Brazil. New collecting data are reported for Pseudodynerus griseus (Fox, 1902) and P. subapicalis (Fox, 1902).

The Neotropical eumenine wasp genus Stenosigma Giordani Soika, 1978 is revised. Stenosigma mariae Ferreira & Hermes sp. nov. and S. panamensis Ferreira & Hermes sp. nov. are proposed as new. An updated identification key for species, new distributional records, and additional information on the species currently recognized within the genus are presented.

Two new species of eumenine wasps were described from Panama and Peru, namely Pirhosigma abregoi Garcete-Barrett & Hermes sp. nov. and P. cambrai Garcete-Barrett & Ferreira sp. nov. Lectotypes are designated for Eumenes deformata barberoi Bertoni and Eumenes superficialis mondaiensis Bertoni. Pirhosigma mearimense putumayense Giordani Soika stat. nov. is treated as a color variation of the typical P. mearimense (Zavattari). Additions to the key by Ferreira et al. (2017) are made and an updated catalog for species included in the genus is provided.