A morphological and molecular analysis of Gryon Haliday (Platygastroidea, Scelionidae) was conducted to provide a taxonomic and phylogenetic context for a species under evaluation as a biological control agent of Bagrada hilaris (Burmeister) (Hemiptera, Pentatomidae). Our analysis revealed that Gryon is polyphyletic and that the biological control agent is not G. gonikopalense, a name that was tentatively applied to this species in 2019. We here describe this species as new, Gryon aetherium Talamas sp. nov., and resurrect the generic name Hadronotus Förster. Morphological characters that delimit our concepts of Gryon and Hadronotus are presented. Based on morphological characters and multilocus phylogenies, we determined that five presently valid scelionid genera belong within Gryon. In total, 15 species are transferred into Gryon from these genera, 215 species are transferred from Gryon to Hadronotus, and 6 species are transferred from Gryon to Dyscritobaeus Perkins. Specimens collected during field studies in California and reevaluation of specimens determined as G. myrmecophilum in Mexico reveal that G. aetherium is adventive in North America.