Abstract
Darwin wasps represent the most species-rich family of parasitoid wasps but remain strongly understudied, with many species yet to be formally described. This is especially the case for the subfamily Campopleginae, a group of koinobiont endoparasitoids of various holometabolan insect orders. We studied most Campopleginae specimens housed at three major Swiss natural history collections, including 1,046 specimens of Hyposoter . We identified 53 of the 71 Western Palaearctic Hyposoter species in Switzerland, including 46 first records, one of which we describe as a new species. Using abundance-based coverage estimators, we estimate 54–61 Hyposoter species in the country. We show that the genus is more species-rich at low altitude and that only three species can be considered as high-altitude specialists, as many show broad altitudinal ranges. We describe Hyposoter beaumonti sp. nov. from Western Switzerland and establish three new synonyms: Hyposoter monensis Galsworthy & Shaw, 2023 of Phobocampe nigra Sedivy, 2004 ( syn. nov. ), the former becoming the valid name because the latter becomes a secondary homonym of Hyposoter niger (Brullé, 1846), Hyposoter castaneus Galsworthy & Shaw, 2023 of Lemophagus curtus Townes, 1965 ( syn. nov. ), and Hyposoter caedator corsicator Aubert, 1960 of Hyposoter caedator (Gravenhorst, 1829) ( syn. nov. ). Our findings underscore the critical role of diversified sampling strategies—including along altitudinal gradients—and up-to-date taxonomic revisions. They also highlight the importance of digitizing and publishing collection data after accurate identification, thereby enhancing the accessibility of ecological and biological information stored in natural history collections for future research.