Morphological diversity of the stridulatory plectrum in assassin bugs (Insecta: Heteroptera: Reduviidae)

The stridulatory apparatus of assassin bugs (Reduviidae) is formed by structures located on the prosternum and the apical part of the labium, yet the morphology of the plectrum has remained poorly characterized. Using scanning electron microscopy (SEM), we documented the morphology of the plectrum and propose a preliminary classification of its diversity. Four main plectrum types were recognized: standard, nodular, plate-like, and visor-like; standard and nodular types were further divided into subtypes. The standard type was the most widespread and occurred in most examined subfamilies, whereas the nodular type predominated in Harpactorinae and was also found in the examined representative of Phimophorinae. The plate-like type was restricted to Salyavatini, while the visor-like type characterized representatives of the Phymatinae complex and occurred in several higher reduviid lineages. We also recorded exceptional cases, including ambiguous specimens, apparent intraspecific variation, and one species lacking a discernible plectrum despite the presence of a stridulatory furrow. These results indicate that plectrum morphology is more diverse than previously recognized and may provide useful characters for comparative morphology and future taxonomic and phylogenetic studies of Reduviidae.