Delimitation of the widely distributed Palearctic Stenodema species (Hemiptera, Heteroptera, Miridae): insights from molecular and morphological data

Species delimitation presents a significant challenge in biology, particularly in systematics. Here, an integrative approach is employed to assess the species boundaries of widely distributed Palearctic Stenodema species. Due to their diversity, wide distribution, and the absence of comprehensive morphological and molecular data for most species, revising Stenodema is both daunting and time-consuming. Our study focuses on detailed examinations of male and female genitalia, coupled with phylogenetic analyses based on two mitochondrial markers (cytochrome c oxidase subunit I and 16S rRNA) and species delimitation analyses. Eight species with wide distributions are reviewed, Stenodema trispinosa Reuter, 1904 is synonymized with S. pilosa (Jakovlev, 1889), and a lectotype for Stenodema turanica Reuter, 1904 is designated. Morphological and molecular data effectively distinguish all species, revealing distinct clades and relationships. Notably, S. calcarata and S. pilosa form a well-supported clade, while S. virens and S. turanica share a lineage with Nearctic species. Stenodema rubrinervis and S. sibirica are morphologically similar and form a distinct clade in all phylogenies. Species delimitation analyses confirm the separation of all studied species, and genetic distances suggest the potential existence of cryptic species within S. calcarata and S. pilosa. This study highlights the advantages of integrative taxonomy in delimiting species with intricate and relatively recent phylogeographic histories.