Browsing by Author "Moran, V C"

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    A commentary on the intellectual health of the nation
    (2007) Vaughan, Christopher L; Reddy, B Dayanand; Noakes, Timothy D; Moran, V C
    The record of high-quality research at South African universities is not as impressive as we may have thought, according to some international rankings. Whatever we might think of these assessments, we have to take them seriously. We suggest ways in which our universities and other institutions of higher learning might raise the level of their game.
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    Adaptation to the host-plant, and the evolution of host specialization, in 'cycad weevils' (Coleoptera: Brentidae)
    (1991) Donaldson, John Sidney; Moran, V C; Hoffmann John
    This thesis deals with host relationships in an enigmatic and seemingly primitive group of weevils belonging to the genus Antliarhinus (Coleoptera: Brentidae). These beetles occur only on species of the cycad genus Encephalartos and appear to retain an ancient association with cycads, a group of plants that were widespread in the Mesozoic era (ca. 200 MYA) before the rise of the angiosperms and which are now represented by 11 genera with relict distributions in the tropics and sub-tropics. The primary aim of this research was to determine the possible causes of narrow host specialization in Antliarhinus zamiae (Thunberg) and A. signatus Gyllenhal, two species which develop exclusively on the ovules of their cycad hosts.
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    Biological control in the management of invasive alien plants in South Africa, and the role of the Working for Water programme
    (2004) Zimmermann, H G; Moran, V C; Hoffmann, J H
    The first biological control project against invasive alien plants in South Africa was in 1913. Initially, invasive cactus species were the only plants in South Africa targeted for biological control. By the early 1960s, the emphasis expanded to include problem plants that threatened the ‘Fynbos’ biome, and latterly to invasive species in other types of natural habitats. Many of the South African projects have been innovative, for example: the use of gall-forming and seed-feeding insect species that have not been used elsewhere; the emphasis on weeds in conservation areas; and the predominance of woody invaders that have been targeted for biological control. Most of these woody plants originated as forestry or agro-forestry introductions, which has created a relatively high incidence of conflicts of interest between conservationists and growers. Recent benefit:cost analyses have demonstrated exceptionally high returns on investment for biological control, even for the least successful of the projects. The inception of the Working for Water programme in 1995 has significantly enhanced biological weed control in South Africa. The benefits include: sustainable funding; investment in research on emerging weeds; a well-organized implementation programme that has increased the impact of biological control in the field; improved international cooperation, particularly in Africa, in concert with the NEPAD initiative; and the recent re-organization of research personnel into cooperative teams that include entomologists, plant pathologists, resource economists and plant ecologists.
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    The biological control of the weed Acacia longifolia by the gall wasp Trichilogaster acaciaelongfoliae: a study of a plant-insect interaction
    (1987) Dennill, George Bentley; Moran, V C
    Weeds are responsible for about 30 percent of all crop losses worldwide, but all weed research, including biological control, receives only about 10% of crop pest control support. The impact of weeds is insidious, diffuse, and complex Increased use of biological control may help to reduce the massive quantity of energy and time now expended for weed control worldwide. Batra (1981) "The vitality of biocontrol of weeds requires two types of evaluation before a project is completed. To maintain financial support it is necessary to show that biocontrol is an economical method of solving certain types of weed problems and to improve the effectiveness of biocontrol in the future, it is necessary to have scientific feed-back. Essentially, the first type of evaluation is concerned with what has been achieved and the second with why the result, either success or failure, has been achieved." Harris (1980a) The biological control of weeds using insects is a young science. The first intentional use of an insect to control a weed was in 1863 in India where the cochineal insect, Dactylopius ceylonicus (Green), was dispersed to control Opuntia vulgaris Miller some 68 years after the accidental introduction of this insect to that country (Goeden, 1978; Moran & Zimmermann, 1984). However, the first full scale attempt at a classical weed biocontrol programme was against Lantana camara L. in Hawaii in 1902 (Goeden, 1978; Harley, 1985a). By 1984 there had been 499 releases of exotic invertebrates and fungi, 488 of which were insects, for the control of 101 weed species in 70 countries (Julien et al., 1984). Despite this marked increase in the number of biocontrol programmes in later years, attempts which failed have rarely been studied or documented and even successes are seldom adequately quantified. This has been implied by Harley (1985a), Julien, (1982), Julien et al. (1984) and Maw (1984). The pressure to produce results and the difficulty of determining the reasons for failures are prohibitive (Dennill et al., 1987; Appendix 6; Goeden & Louda, 1976). The advancement of this science thus relies heavily on the study of its successes. This thesis is an evaluation of the gall wasp Trichilogaster acaciaelongifoliae as a biocontrol agent for the weed Acacia longifolia in South Africa. The wasp has been successful, and, in accordance with Harris (1980a), my aims were twofold: to quantify that success and to provide reasons for it. This information not only produces guidelines ii for the future selection of biocontrol agents, sensu Harris (1980a), but also serves as a means of enhancing our understanding of insect-plant relationships. In addition, this thesis provides an indication of the potential of gall forming insects in biological control of weeds. Gall formers have seldom been used to control weeds (Julien, 1982; Maw, 1984). Since their effects are indirect compared with those of insects attacking vegetative plant parts, their potential for weed biocontrol has apparently been underestimated in the past by some authors (Goeden, 1983; Harris, 1973; Hokkanen, 1985a). The present attempt is the first ever in which a gall forming hymenopteran has been used to control a weed, and shows beyond doubt that certain gall formers can have strong potential in this field. Chapter 1 concerns the establishment of the wasp, its population increases, dispersal, host-seeking, and the reduction of reproductive potential of A. longifolia populations. The development of new techniques that were necessary for the determination of these parameters is included. Emphasis is placed on the reasons for the successful establishment and rapid population increases observed. The potential of the insect for suppressing both reproduction and growth of the weed is great, and is examined in detail in Chapter 2. The phenological information obtained during the course of this study showed important inadequacies in the knowledge of the phenology of A. longifolia. This is rectified in Chapter 3 in which the implications of an incomplete understanding of weed phenology for biological control are emphasised. In particular, the resource allocation between reproduction and growth of the plant provides a crucial setting for the next chapter. In Chapter 4 the nature of the galling by T. acaciaelongifoliae and its relation to the phenology of A. longifolia are examined in order to explain how the wasp is able to exploit its host so effectively under South African conditions. Chapter 5 deals with the release of the wasp throughout the South African range of the weed and the identification of regions in which its performance appears inadequate. The climates of South Africa and Australia are compared to determine to what degree the establishment of T. acaciaelongifoliae in various regions in South Africa is related to the climate of the regions in which the wasp was collected in Australia. This chapter includes maps illustrating weed distribution, co-ordinates for all release points, and documents the method whereby the wasps were released. Chapter 6 is an essay dealing with the implications of the study, both practical and theoretical. Recommendations regarding the future selection of biocontrol agents are made, with emphasis on perspectives emerging from this thesis, and the future role of the wasp in the control of A. longifolia in South Africa is discussed.
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    Oviposition behaviour of Neltumius arizonensis Schaeffer (Coleoptera: Bruchidae) : a biological control agent of Prosopis spp. in South Africa
    (1995) Strathie, Lorraine Wallace; Hoffmann, J H; Moran, V C
    Little has been documented on the biology of Neltumius arizonensis Schaeffer. This bruchid is native to the south-western United States of America and is a prospective biological control agent of Prosopis spp. in South Africa. The primary objective of this study was to examine and quantify the oviposition behaviour of N. arizonensis females under different conditions to determine whether eggs of conspecifics or of another bruchid species, Algarobius prosopis (LeConte), affected oviposition. Diet, the number of mates, the duration of access to mates, and the variety of Prosopis pod provided for oviposition all affected the fecundity of N. arizonensis. Optimal conditions for N. arizonensis oviposition included: a diet of pollen pellets in solution, constant access to a limited number of mates, and mature, undamaged Prosopis pods of the 'mottled-purple' variety. The physical structure of the surface of Prosopis pods, observed by scanning electron micrography, did not reveal trends in characteristics among pod varieties that could be linked to the oviposition preferences of N. arizonensis. The rate of oviposition in N. arizonensis peaked between the third and eighth day after emergence from pods and was highest during the first hour when females that had been deprived of pods for at least three days, were provided with pods. Each N. arizonensis female laid an average of about 80 eggs during her lifetime, which was about 3 5 days on average. An event-recording computer programme was developed to quantify the oviposition behaviour of N. arizonensis when females were provided with one of four types of Prosopis pods for one hour: (a) pristine pods, (b) pods with conspecific eggs, (c) pods with A. prosopis eggs deposited within slits, and (d) pods with egg-free slits. Analyses of time budgets indicated that pod type had no significant effect on behaviour, although some activities differed significantly with the type of pod provided, but probably only as a result of the greater number of eggs laid on some pod types. Certain activities i.e. inspection of the pod surface, remaining stationary, and scraping of the ovipositor across the surface prior to egg deposition, occupied significantly more time on pods than other activities. Pod type did not affect the total time females spent on pods, nor the frequency of visits to pods. The availability of clean seeds did not affect the quantity of eggs deposited and the rate of oviposition did not differ significantly on pods of different types.