Introduction

Soldier beetles (family Cantharidae Imhoff, 1856) represent one of the major lineages within the superfamily Elateroidea Leach, 1815, comprising over 6600 species worldwide and ranking second in diversity only to click beetles (Kundrata 2026). The family exhibits particularly high diversity in the Oriental and eastern Palaearctic regions, where many cantharid lineages originated and to which many remain restricted, as exemplified in the genus Lycocerus Gorham, 1889 sensu lato (Okushima 2005). This pattern is also exhibited in Stenothemus Bourgeosis, 1907.

Since Wittmer’s (1974) revision, the genus Stenothemus has become increasingly diverse, with dozens of new species discovered in recent years (Okushima and Satô 1997, 1999; Švihla 2004, 2005, 2011; Yang et al. 2014, 2021a, 2021b; Hsiao 2015; Hsiao et al. 2016; Ge et al. 2021a, 2021b, 2021c). Currently, it contains approximately 100 species widely distributed across the East Palaearctic and Indochina (Ge et al. 2021a, 2021b, 2021c; Yang et al. 2021a, 2021b). To facilitate taxonomic organization, a species-group classification was first introduced by Švihla (2005) to this genus and subsequently adopted by Yang et al. (2014) and Ge et al. (2021b, 2021c). To date, three species groups have been proposed, including the S. harmandi group (Švihla 2005), the S. notaticollis group (Ge et al. 2021c), and the S. laterophysus group (Ge et al. 2021c). These groups are primarily distributed in the Himalayas, with a few species extending into southwest China, a region recognized as a hotspot of cantharid diversity (Liu et al. 2022). Here, we recognize an additional group from this area, which includes S. volaticus Champion, 1925 and its sibling species (Wittmer 1974; Švihla 2004; Yang et al. 2021b), as well as two new species discovered from Xizang, China.