The cactus moth, Cactoblastis cactorum (Berg), is native to South America. Since its unintentional arrival to the United States in 1989 and to Mexican islands in 2006, it has become a serious threat to the diversity of both wild and cultivated species of Opuntia Mill, in North America. The native ecological host range of C. cactorum has not been directly ascertained and host acceptance is unclear. Taxonomic nomenclature of Opuntia spp. has been confusing, contradictory, and rapidly changing, leading to inaccurate conclusions about host plant use by C. cactorum in its native South American range. This study was conducted to better understand the biology and ecology of C. cactorum in Argentina by evaluating, under laboratory conditions, the insects’ performance (survivorship, development time, potential fecundity) on 8 Opuntia spp. occurring in Argentina. Feeding trials were conducted on 5 Opuntia spp. native to Argentina and 3 Opuntia spp. native to Mexico. Cactoblastis cactorum larvae failed to feed on 2 native Opuntia spp., and had their greatest performance on the North American O. ficus-indica (L). Mill, and O. robusta H. L. Wendl. ex Pfeiff., and the South American O. arechavaletae Speg. Because the insects for the experiments were originally collected on O. ficus-indica, a reciprocal cross feeding experiment with insects collected on O. megapotamica Arechav. was also conducted to test for a potential host plant-mediated local adaptation effect. Some evidence for host plant adaptation was detected in populations collected on the South American host, O. megapotamica. Local adaptation, as documented here, could have consequences for the invasion process of C. cactorum in North America.