Levels of damage caused by Melanterius servulus Pascoe (Coleoptera : Curculionidae), a seed-feeding weevil introduced into South Africa for biological control of Paraserianates lophantha (Fabaceae)

Melanterius servulus Pascoe is a seed-feeding weevil that has been introduc ed into South Africa for biological control of Paraserianthes lophantha (Wi lld.) Nielsen, a leguminous perennial tree from Australia. Since the initia l releases of the weevil on the Cape Peninsula in 1989, no attempts had bee n made to determine the impact of M. servulus on seed production of the wee d. In this study, surveys were conducted throughout the Peninsula to obtain seeds that were X-rayed to distinguish those which were healthy from those that had been damaged by adults or larvae of M. servulus or other types of insects. Levels of seed damage caused by M, servulus increased with the le ngth of time that the beetles had been established in the vicinity of infes tations of the weed, and decreased with increasing distance from the neares t release site. Seed damage peaked at 75 % on isolated P. lophantha plants but never surpassed 65 % in thickets of the weed. The beetles showed no app arent preference for any particular type of habitat in which the host plant s were growing, and damage was not related to the position of the seed pods within the tree canopy. The study indicated that M. servulus disperses slo wly (approximately 1 km per year) and that population numbers increase grad ually. The beetles are thus expected to fulfill a much greater role as biol ogical control agents of P. lophantha in the future.