In the whole of Argentina and Chile, southern South America in this paper, 20 species of the genus Aphis hosted in species of Asteraceae were known; eleven of them are native South American, and those introduced are mostly polyphagous and widespread. The Chilean regions and the Argentine provinces in which each one of them is known, as well as the host plants on which it has been recorded, are listed. New data of 15 of them are presented, with several first records in different Argentine provinces or hosted on diverse plants: The knowledge of A. conspicua and A. fuentesi, which were recently described living on species of Baccharis, is improved from specimens respectively collected on Senecio and Gutierrezia. A. rogerblackmani Nieto Nafra, Ortego Mier Durante sp. n. is described from apterous and alate viviparous females, oviparous females and males collected on Baccharis in Argentina. Other four species are described from apterous and alate viviparae: A. gutierreziae Ortego, Mier Durante Nieto Nafra sp. n., collected on species of Gutierrezia in Argentina, A. hyalis Mier Durante, Nieto Nafra Ortego sp. n., collected on Hyalis argentea in Argentina, A. pulverea Nieto Nafra, Moreno-Gonzlez Ortego sp. n., collected on species of Senecio in Chile and Argentina, and A. sanrafaelina Ortego, Mier Durante Nieto Nafra sp. n., collected on Tagetes mendocina, Thymophylla pentachaeta and Pectis odorata in Argentina. The intraspecific diversity of Aphis pulverea has been analysed by a principal component analysis followed by hierarchical clustering of principal components. An identification key to viviparous females of the species of Aphis hosted in Asteraceae and known in southern South America is presented.