An investigation on factors influencing the rearing and success of biological control agents of Gonipterus sp. n. 2 (Coleoptera: Curculionidae)

Gonipterus scutellatus species complex is a cryptic species that feeds on Eucalyptus leaves. Both the adult and larval stages cause high levels of defoliation. Gonipterus sp. n. 2 is the species present in South Africa and Anaphes nitens was released as a biological control agent. However, Gonipterus spp. populations have continued to cause economic damage and various countries continue to seek additional biological control agents. This dissertation focused on understanding how natural enemies interact if multiple species are released in a biological control programme. The biology of one potential parasitoid of Gonipterus sp. n. 2, Centrodora damoni was investigated. It was shown that the parasitoid’s longevity, host age preference and developmental time are ideal for it to be a successful biological control agent. The success of the biological control of Gonipterus sp. n. 2 was also investigated by studying the reproductive development of the beetle and linking it to its seasonal egg production in the laboratory. The preoviposition period for Gonipterus sp. n. 2 was 30 days and oviposition occurred when the beetles were four weeks of age. Various factors that influence the rearing techniques were considered in this study including how the techniques affect preparation for releases. Four parasitoids that were reared in the laboratory, namely Anaphes inexpectatus, Centrodora damoni, Cleruchoides noackae and Selitrichodes neseri were measured to investigate the effect of rearing on parasitoid fitness using body size as a proxy across nine generations, six generations, nine generations and five generations respectively. Rearing reduced body size significantly over two generations for C. noackae and C. damoni. S. neseri had significant differences in body size between some generations but the first and last generations studied had no differences. A. inexpectatus did not exhibit any loss in body size across generations.