Larvae of Oliera argentinana, Brethes 1916 (Lepidoptera: Cecidosidae) were rediscovered inducing spindle-shaped galls enclosed within swollen stems of Schinus (Anacardiaceae) in central Argentina and Rio Grande do Sul, the southernmost state of Brazil. Male, female, immature stages, and plant galls of O. argentinana are redescribed, using optical and scanning electron microscopy. The genus Oliera Brethes, 1916, previously a junior synonym of Cecidoses Curtis, 1835, is revalidated, by comparing morphological characteristics within the family and through an analysis of mitochondrial (COI) DNA sequences, including putative members of the four Neotropical cecidosid genera. Information on preliminary Cecidosidae phylogeny and taxonomy is also provided.
