Integrative taxonomy of Diamesus Hope, 1840 (Coleoptera: Silphinae) is presented. Adults of D. bimaculatus Portevin, 1914 (endemic to Taiwan) and D. osculans (Vigors, 1825) (widely distributed from northern India to Australia) are redescribed, keyed and figured, including characters of the male and female genitalia of both species. Variation in elytral maculation in D. osculans is discussed and illustrated. The absence of diagnostic differences of D. osculans var. reductus Pic, 1917 from D. osculans is discussed, and the former name is confirmed as a junior subjective synonym of D. osculans. Types of all three names available were studied; a lectotype and paralectotypes are designated for the name D. osculans var. bimaculatus Portevin, 1914. Molecular phylogenetic analysis confirms the genus Diamesus is sister group to the genus Necrodes Leach, 1815, and D. osculans and D. bimaculatus are two, well supported clades. Detailed data on the distribution of D. bimaculatus and D. osculans are presented and mapped. Species distribution models for both species were created and interpreted. Diamesus osculans is reported for the first time from India: Uttarakhand, China: Anhui, Hainan, Hunan, Jiangxi, Shaanxi and Zhejiang Provinces, and Australia: Victoria; it is also recently confirmed from Taiwan, being sympatric in distribution there with D. bimaculatus. Available data on the ecology and seasonality of both species of Diamesus are also discussed.
© 2023. The Author(s).