From Southeast Asia to global: phylogeny, biogeography and character evolution of the thread-legged bug tribe Leistarchini (Hemiptera: Reduviidae: Emesinae)

The thread-legged bug tribe Leistarchini (Hemiptera: Reduviidae: Emesinae) is a cosmopolitan and diverse group characterized by a highly disproportionate spatial distribution across zoogeographic regions. Due to a historical lack of phylogenetic focus, the internal relationships and evolutionary history of the tribe remain poorly understood. In this study, we provide the first robust phylogenetic framework for Leistarchini by integrating molecular data from mitochondrial genomes and nuclear rDNA (88 taxa, 19 937 bp) with universal single-copy orthologs (24 taxa, 667 loci). Our results support the monophyly of Leistarchini and identify five major clades, including a newly described genus Calliemesa gen. n. Our findings further reveal that the five most species-rich genera (Nesita, Orthunga, Pleias, Ploiaria and Tinna) are either paraphyletic or polyphyletic as currently circumscribed. Molecular dating and biogeographic reconstructions suggest a Southeast Asian origin for the Leistarchini crown group during the late Palaeocene (ca. 57 Ma). Early diversification appears to have been driven by Paleogene geological and climatic shifts in Southeast Asia, while multiple intercontinental dispersals since the middle Eocene into the Afrotropics, Madagascar and the New World shaped the current global distribution. Ancestral state reconstructions indicate that the Leistarchini ancestor possessed a well-developed posterior pronotal lobe and a three-segmented protarsus. Subsequent evolutionary trajectories involved four independent transitions toward a shortened posterior pronotal lobe, and four separate reductions in protarsal segmentation.