Browsing by Author "Impson, F A C"

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    Biological control of Acacia cyclops in South Africa : the role of an introduced seed-feeding weevil, Melanterius servulus (Coleoptera: Curculionidae), together with indigenous seed-sucking bugs and birds
    (2005) Impson, F A C; Hoffmann, John; Moran, Cliff
    Acacia cyclops A. Cunn ex G. Don, or rooikrans (Fabaceae), of Australian origin, is an invasive environmental weed in South Africa where it threatens the unique vegetation of the Cape Floral Kingdom. The invasiveness of the plant in South Africa is, in part, due to its high annual seed-yields, together with the suitable climatic and edaphic factors found here. This study investigated the role of a seed-feeding weevil, Melanterius servulus, which was first introduced into South Africa during 1991, as a biological control agent of A. cyclops seeds, together with the combined effects of indigenous seed-sucking bugs and birds. The weevils utilise filled green pods of A. cyclops for adult feeding, oviposition and larval development and completely destroy seeds during these activities. Examination of the reproductive phenology of A. cyclops showed that seeds are produced annually, during summer and that the presence of filled green pods on the plants coincides with the period of reproductive activity of the weevils. Melanterius servulus populations have established readily at all the original release sites, and within four years of release, damage levels to seeds commonly reached 90%. The weevils have dispersed at an average rate of approximately 2 km per year. Since becoming established in South Africa. the seeds of A. cyclops have been utilised by a variety of generalist vertebrate and invertebrate organisms. Indigenous polyphagous alydid bugs feed on the mature seeds, rendering a portion of the crop inviable when damage levels are high (more than five feeding-punctures per seed). Several bird species are attracted to and feed on the fleshy aril that surrounds theseeds of A. cyclops. Passage of the seeds through the gut of birds enhances germination rates. There is a synergetic relationship between alydids and birds because seeds with low levels of alydid feeding (one to four punctures per seed) germinated more readily after passage through birds than seeds that were not eaten by birds.
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    Dasineura rubiformis (Diptera: Cecidomyiidae), a new biological control agent for Acacia mearnsii in South Africa
    (Academy of Science of South Africa, 2008) Hoffmann, J H; Impson, F A C; Kleinjan, C A; Post, J A
    Acecidomyiid midge, Dasineura rubiformis, is the most recent addition to the suite of biological control agents that have been deployed in South Africa against invasive Australian Acacia species. This insect is associated with Acacia mearnsii (black wattle), which is extremely invasive, but also an important agro-forestry species, in South Africa. It induces development of galls in the flowers of A. mearnsii, thereby preventing pod development and reducing the reproductive capacity of the plants. The useful attributes of this economically important plant species should not be affected by the introduction of D. rubiformis. The midge is established in the vicinity of Stellenbosch, where it is increasing in abundance. Studies have been initiated to (i) evaluate the performance of the midge; (ii) confirm that galling does not cause a reduction in vegetative growth of A. mearnsii; and (iii) determine the potential effectiveness of D. rubiformis as a biological control agent of A. mearnsii. All indications are that the insect has the potential to become an excellent seed-reducing biological control agent of A. mearnsii.