Integrative Taxonomy Clarifies Species Limits in Two Closely Related Solitary Wasps: Pachymenes ater and Pachymenes ghilianii (Hymenoptera: Vespidae: Eumeninae)

Species delimitation in morphologically conserved groups poses a significant challenge for traditional taxonomy. In the Neotropical wasp genus Pachymenes (Hymenoptera: Vespidae: Eumeninae), two putative sister species—Pachymenes ater and P. ghilianii—have historically been distinguished by a limited set of ambiguous morphological characters, often complicated by intraspecific variation and overlapping geographic distributions. Here, we apply an integrative taxonomic framework combining morphological, molecular, and geographic evidence to test species limits between these two taxa. We reassess previously proposed diagnostic traits and explore the utility of additional characters across multiple lines of evidence. Our results indicate that some morphological characters traditionally used for identification are insufficient for clear separation of species, while other, previously overlooked traits offer improved resolution. Molecular data further support species distinction and provide new insights into the evolutionary relationship between P. ater and P. ghilianii. This study highlights the importance of combining diverse data sources for robust species delimitation in solitary wasps and contributes to a better understanding of species boundaries within Eumeninae.