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

## TL;DR

This study uses multiple methods to clarify the species boundaries between two similar wasps, Pachymenes ater and Pachymenes ghilianii, improving their classification and understanding.

## Contribution

The study introduces an integrative approach combining morphology, genetics, and geography to resolve species limits in a morphologically similar wasp group.

## Key findings

- Traditional morphological traits are unreliable for distinguishing Pachymenes ater and P. ghilianii.
- New morphological features and genetic data support their classification as separate species.
- An integrative method improves species delimitation in morphologically conserved wasp groups.

## Abstract

Telling closely related species apart can be difficult when they look very similar on the outside. This problem occurs in a group of solitary wasps found in Central and South America, where two suspected sister species have long been hard to separate because they share many body features and often live in the same regions. In this study, we investigated whether these two wasps truly represent separate species by examining them in several ways. We looked closely at body structures, including some features that had not been considered before, and compared them with modern genetic information and data on where each form is found. We discovered that some of the traits traditionally used to identify the species are not reliable, but other, previously overlooked features help distinguish them more clearly. The genetic evidence also supports the idea that they are two separate species and reveals how they are related to each other. By bringing together different types of information, our study shows a more accurate way to define species in groups that appear very uniform. This approach can improve the classification of solitary wasps and help guide future research on their diversity and conservation.

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.