Hoplonannus McAtee & Maloch, 1925 comprises three species described from Central America. Females of all these species are known only from brachypterous specimens. This paper describes the first South American species of the genus, Hoplonannus australis sp. nov. The new species differs from its congeners, in females, by the submacroptery, presence of ocelli and a basal bulge in the seventh sternite; in males, it differs by the presence of a process in the eighth tergite and the right paramere bifurcate apically, with branches subparallel. These traits entail a new diagnosis for the genus.