Specimen and species history of Mesitius ghilianii Spinola (Hymenoptera, Bethylidae)

The flat wasps subfamily Mesitiinae (Hymenoptera, Bethylidae) are rarely collected using standard entomological sampling methods, resulting in a marked scarcity of specimens in natural history collections and persistent taxonomic uncertainty within the group. Mesitius ghilianii Spinola, 1853, which is the first species historically associated with what is now recognized as Mesitiinae, has a particularly complex nomenclatural history and is known from a single surviving historical specimen, designated as lectotype. Here, we report the restoration, redescription, and historical reassessment of this specimen, preserved in the Museo Regionale di Scienze Naturali, Turin, Italy. We document an inexpensive, non-toxic restoration protocol based on ammonia cleaning, mechanical debris removal with clinical needle, and controlled rehydration, which allowed the stabilization and partial repositioning of a nearly two-century-old point-mounted specimen. Following restoration, we provide a detailed modern redescription of the female, including diagnostic morphological characters of the head, mesosoma, wings, legs, and metasoma, supported by high-resolution imaging. In addition, we reconstruct the provenance and curatorial history of the specimen, tracing its collection by Vittore Ghiliani in Sicily and its subsequent study by Massimiliano Spinola, and we review the long and often contradictory taxonomic history of M. ghilianii and related taxa. This study underscores the irreplaceable scientific value of historical museum specimens for resolving longstanding taxonomic problems in poorly collected groups and highlights the importance of affordable restoration techniques for safeguarding type-level material. Our results provide a robust morphological baseline and historical framework for future integrative revisions of Mesitius and particularly M. ghilianii , which represent the genus-type of Mesitiinae and the type-species of Mesitius respectively.