Objectives, Constraints, and Tactics in the Biological Control of Mesquite Weeds (Prosopis) in South Africa

Abstract

Two species of seed-feeding bruchid beetles, Algarobius prosopis (Le Conte) and A. bottimeri Kingsolver, have been released in South Africa for the biological control of Prosopis taxa. A. prosopis destroys large numbers of mesquite seeds in the mature pods but, alone, it cannot adequately control the weed. It is doubtful whether the recent releases of A. bottimeri will be of any significance. Of the hundreds of herbivorous insect species that feed on mesquite in the Americas, only two additional ones, Mimosestes protractus (Horn) and Neltumius arizonensis (Schaeffer) (both Coleoptera: Bruchidae), seem to be suitable for importation into South Africa, at this stage, because they are specific to Prosopis, thrive on the mesquite taxa that are weeds in South Africa and, most importantly, have the potential to reduce the invasiveness and spread of mesquite without diminishing the valuable attributes of the plants, particularly the use of the mature pods as a source of fodder. The importation of these two additional agents may enhance the level of control achieved by A. prosopis, because they attack mesquite seeds in the green pods. Further prospects for management of mesquite in South Africa are also discussed and include: (i) the implementation of an integrated program that maximizes seed destruction by A. prosopis and (ii) the initiation of debates that may lead to a decision to forfeit the pods as a fodder, thus greatly expanding the number of biological control agents that would be available for screening against invasive Prosopis taxa in South Africa.