It is shown that under the name Mocis frugalis (F., 1775), considered to represent a widespread pest of graminaceous crops in the Eastern hemisphere and the Pacific, two species have been hitherto confused. Populations from Africa and Arabian Peninsula are described as Mocis proverai sp. n. The main characters which distinguish the African-Arabian M. proverai from M. frugalis of Asia and the Pacific are found in the genitalia, especially the configuration of the male vesica and female bursa copulatrix.