We describe Diastrophus colombianus Nieves-Aldrey sp. nov., a gall inducer on Rubus glaucus Bentham (Rosaceae) in Colombia. This is the first reliable record of a species of Diastrophus Hartig, 1840 (Hymenoptera: Cynipidae) and of an herb gall wasp (Cynipidae: “Aylacini”) native to the Neotropical region. The phylogenetic relationships among the members of Diastrophus—D. colombianus and the species considered by a previous study—were inferred from adult morphological and gall characteristics. Our results suggest that D. colombianus is more closely related to a clade composed of Diastrophus austrior Kinsey, Diastrophus rubi (Bouché), Diastrophus fragariae Beutenmüller, and Diastrophus tumefactus Kinsey.