Abstract
Simulium weji sp. nov. is described based on the reared females, reared males, pupae and mature larvae collected from Tharn Thong Waterfall in Lampang Province, Thailand. This new species is assigned to the tuberosum species-group within the subgenus Simulium s. str., and seems to be closely related to S. rufibasis Brunetti and four other allied species, reported from India and Thailand, by having a pair of hair clusters on the ventral surface of the seventh abdominal segment of the female, which are, though, much longer and fewer in this new species. This new species seems to be also related to S. nigrifacies Datta from India and S. puliense Takaoka from Taiwan, by having the similar arrangement of six short pupal gill filaments, but is easily differentiated from these known species by the small cone-shaped tubercles on the head and thoracic integuments.
