Technical Abstract: Anredera cordifolia (Tenore) Steenis (Basellaceae) is a perennial climber native to southern South America. Known as Madeira vine, it has become a serious environmental weed in Australia, South Africa, Hawaii, New Zealand and other Pacific islands, where it forms mats over trees and shrubs disrupting forests, costal areas and riversides. Field surveys conducted in Argentina, proved Plectonycha correntina Lacordaire (Coleoptera: Chrysomelidae) to be a promising biocontrol agent against A. cordifolia. Larvae and adults feed on the leaves. The host range was evaluated by no-choice larval survival tests and adult feeding and oviposition choice tests. The sixteen test plants were selected from the Basellaceae (4 species), Portulacaceae (4), Crassulaceae (3), Cactaceae (3) and Aizoaceae (2) families. Larval development could only be completed on species of the Basellaceae (A. cordifolia, Anredera krapovickasii (Villa) Sperling, Basella alba Linné, Ullucus tuberosus Caldas). None of the other test plant species could sustain larval development for longer than 96 hours. In the multiple-choice test involving plant species outside the Basellaceae family, both in the presence and in the absence of A. cordifolia, P. correntina showed an almost complete preference for its natural host. Larvae that emerged from the few eggs laid on Talinum paniculatum (Jacquin) Gaertner (Portulacaceae) and Pereskia grandifolia Haworth (Cactaceae) died 48 hours after emergence without feeding. In the test among the Basellaceae species, feeding and oviposition preference of P. correntina for A. cordifolia and B. alba were significantly higher than for A. krapovickasii and U. tuberosus. In multiple-choice and paired-choice feeding and oviposition tests as well as in fecundity tests, P. correntina displayed a significantly greater preference for Madeira vine than for B. alba. The results indicate that the host range of P. correntina is restricted to the Basellaceae family, with A. cordifolia as its primary host. Consequently, we consider P. correntina a safe and promising biocontrol agent for Madeira vine in countries such as Australia and New Zealand where no other Basellaceae species occur, as well as in South Africa where only one indigenous Basellaceae species have been reported.