A review of the effectiveness of seed-feeding bruchid beetles in the biological control of mesquite, Prosopis species (Fabaceae), in South Africa

Prosopis species were introduced into South Africa from the Americas as agroforestry trees to provide fuel wood, shade and fodder. At least four species have become naturalized, widespread and problematic on farmlands, particularly in the dry northwestern region of the country. In an attempt to limit the reproductive potential of these plants, while preserving their beneficial attributes, biological control of Prosopis species in South Africa has been restricted to the use of seed-feeding agents. To date, three seed-feeding bruchid species, from the southwestern United States of America, have been released in South Africa for control of prosopis. Algarobius prosopis (LeConte) was released in 1987, A. bottimeri Kingsolver in 1990 and Neltumius arizonensis Schaeffer in 1993. Algarobius prosopis and N. arizonensis have established and are widespread. Algarobius bottimeri has apparently failed to establish. Algarobius prosopis and N. arizonensis have the potential to destroy large numbers of prosopis seeds, but their progress is hampered by foraging livestock which devour the pods before they are utilized by the beetles. This report updates a 1991 review of prosopis biocontrol in South Africa. The biology of N. arizonensis is described and the role of native parasitoids and competitive interactions between the three bruchid species. in limiting the impact of these agents, is discussed. The increasing extent of the problems caused by prosopis in South Africa and greater awareness of losses of scarce underground water, which is utilized by prosopis, may dictate future tactics far biocontrol of this weed. The use of agents other than seed feeders will probably become acceptable in the near future as landowners increasingly come to realize that the problems caused by the plants far outweigh the benefits that are derived from them.