Revision of Formosargus James, 1939 (Diptera: Stratiomyidae): five new species in an otherwise rare genus and Amsaria Adisoemarto, 1974 as a generic synonym

The Australian and Oriental genus Formosargus James, 1939 (Stratiomyidae: Sarginae), until recently only known from three described species - F. kerteszi James, 1939, F. melanogrammus Lessard and Woodley, 2020, and F. variegatus James, 1969 - is herein revised. The monotypic sargine genus Amsaria Adisoemarto, 1974 is considered to be a synonym of Formosargus, and examination of material accumulated over the years resulted in the description of five new species to science: F. berezovskiyi sp. nov., F. borneensis sp. nov., F. mangoleensis sp. nov., F. trivittatus sp. nov. and F. woodleyi sp. nov. The genus, which was previously thought to be restricted to the Oriental Region only - known from species from Taiwan and the Philippines, though recently discovered in northern Australia and West Java, Indonesia (F. melanogrammus) - is here shown to be widespread in Southeast Asia. It reaches not only the transition zone between the Oriental and Australian regions and beyond, with first records from Papua New Guinea, but is also reported from the continental portion of Asia, with first records from Malaysia and Thailand. Rare in collections and with virtually no biological information available, Formosargus may have a hidden diversity in the Southeast Asia tropical wet forests, so additional species are expected to be found with future collecting efforts in the area. A key to all the species of Formosargus (which now includes 10 species), detailed descriptions of the species, and a map expanding the geographical distribution of the genus are also presented.