There are at least five Prosopis species, one with two subspecies, that have become naturalized in South Africa. All were introduced to provide shade in almost treeless semi-desert areas and because they produce large quantities of nutritious pods for stock feed. Three of the taxa have now become problem weeds, particularly in the arid northwestern Cape, and a fourth has the potential to become a problem. The invasiveness of Prosopis spp. can largely be attributed to the annual production of large quantities of seeds. Two seed-feeding bruchids, Algarobius prosopis (LeConte) and Algarobius bottimeri Kingsolver, from North America were released recently in South Africa for biological control of Prosopis spp. Both bruchid species have established readily and are destroying a considerable proportion of the seeds. The biological control of Prosopis spp. using seed-feeding insects is considered an important component in the proposed integrated control of Prosopis spp., which will also rely on intensive utilization of these invasive plants.