A new species of Masarina Richards 1961, M. gabymariae, associated with Hermannia (Mahernia) diffusa L., Malvaceae: Sterculioideae) is described from a relict patch of Swartland Granite Renosterveld at Darling in the Western Cape Province of South Africa and the hitherto unknown female of M. ceres Gess 1997 is described from Graafwater in the same province. Supplementary collecting data are given for three other species of the genus, M. hyalinipennis Richards 1962, M. mixta Richards 1962 and M. strucki Gess 1988.