Competitive interactions between two bruchid species (Algarobius spp.) introduced into South Africa for biological control of mesquite weeds (Prosopis spp.).
Algarobius prosopis and A. bottimeri, both seed-feeding species from North America which were introduced into South Africa for the biological control of mesquite weeds [Prosopis spp.], have not been entirely successful. A. prosopis is prolific and damaging while A. bottimeri has become established, but is scarce and confined to one locality. The survival of immatures, adult mass, sex ratios and fecundity was measured for individuals in insectary-reared colonies of A. prosopis and A. bottimeri on 5 different mesquite taxa that are naturalized in South Africa, including a South American species, Prosopis chilensis and 4 North American taxa, P. velutina, P. glandulosa var. torreyana, P. glandulosa var. glandulosa and hybrids, possibly of all 4 of these species. On all 5 mesquite taxa, survival from egg to adult was lower in A. bottimeri than in A. prosopis. Though potentially more fecund than A. prosopis, females of A. bottimeri that mated only once produced few viable eggs. When neonates competed for the same seed, A. prosopis was dominant and A. bottimeri was usually excluded. It is concluded that mass rearing and releases of A. bottimeri should be discontinued because all indications are that this species will not have a noticeable impact on the weed.