Masters Degrees (Conservation Ecology and Entomology)
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- ItemThe sustainability of biochar use(Stellenbosch : Stellenbosch University, 2024-03) Feni, Abongile Jackie; Malgas, Rhoda Ronette; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Biochar is a plant-based material that has been extensively studied for its potential in soil remediation, plant growth, and addressing industrial issues like water purification and climate change mitigation. However, there are two main challenges to its application in agriculture, that is, a lack of research- based outside Africa, and the interdependence of food, energy, and water resources. As urbanization in Africa increases, agricultural production areas have expanded to ensure food security, but this has led to the expansion of natural areas and habitats, posing threats to native endemic plants. South Africa's Cape Floristic Region (CFR) has been negatively affected, with some species extinct or threatened. Fynbos, a fire-driven vegetation type, is known for its diverse plant species, including iconic species like buchu, rooibos, and honeybush, which have medicinal properties that benefit local communities. A holistic approach to biochar research is needed to overcome these challenges, considering the interconnected nature of these interconnected resources. This dissertation focuses on the Sustainable Development Goals (SDGs) to create peace, and human prosperity, reduce environmental degradation, and ensure sustainability. It aligns with the South African Department of Science and Technology's Biotechnology Strategy, which aims to improve the economy by integrating biotechnology and indigenous knowledge. The SDGs that are aligned include i) SDG 2 (ensuring zero hunger); ii) SDG 3 (ensuring good health and well-being); iii) SDG 6 (ensuring clean water and sanitation); iv) SDG 7 (ensuring affordable and clean energy) and lastly v) SDG 15 (Protecting, restoring, and promoting sustainable use for life on land). With three research chapters, the thesis investigates the potential of biochar by i) conducting a systematic review to analyse the results and draw conclusions based on research on agriculture production; ii) evaluating the interaction between biochar from invasive plant species and seed germination of three Fynbos medicinal plant species using an experiment and lastly iii) focusing on the interactions between food, energy, and water as integrated components for opportunities for optimization and innovation for smallholder farmers in South Africa, using a nexus approach. The results from these chapters showed that biochar does have the potential to i) improve agricultural production (positive response from different plants investigating the effects of biochar on seed germination, growth, yield, response to drought, salinity, pest, diseases, and allelopathy), ii) there is a slightly positive interaction between invasive plants biochar and germination of the seeds of the three medicinal plants and lastly, iii) using initiatives like alien invasive plants clearing on water sources, creating opportunities for farmers to use the alien plants for producing biochar and bio-oil or biofuel to improve the food, energy, and water interconnection. Considering the research in the context of the sustainable development goals (SDGs), this research focuses on applying biochar to enhance agricultural production to address SDGs 2, 6, and 7 in response to the agricultural needs of small-scale farmers in Africa. More specifically, in South Africa, it also explores the three Fynbos seeds in question, based on endemic species with a biocultural and commercial value that relates to SDGs 3 and 15.
- ItemThe effects of landscape transformation, isolation, and habitat quality on plant-pollinator interactions in conservation corridors(Stellenbosch : Stellenbosch University, 2024-03) Khan, Zahra; Pryke, James; Gaigher, Rene; Van Schalkwyk, Julia; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The KwaZulu Natal Midland’s natural areas are comprised mainly of grasslands, wetlands, and indigenous forest which are highly threatened by agricultural expansion and commercial forestry. Many endemic plant and animal taxa occur in this region and require protection due to competing land uses. To mitigate biodiversity loss in these rich landscapes, conservation corridors have been implemented creating habitat and conduits for dispersal across the harsh matrix of alien trees. While corridors fulfil the functions of habitat and conduits for dispersal, there is significant fragmentation and habitat loss to forestry which are known to be the drivers of biodiversity loss worldwide. In light of this, my study explores plant-pollinator interactions to determine whether corridors are effectively preserving biodiversity and its function. I first explored the differences in plant-pollinator interaction networks between four different landscape contexts within conservation corridors. Interactions between flowering plants and flower visitors were observed in each landscape context and local environmental variables measuring habitat quality, (provision of food for the pollinators) and landscape variables measuring isolation (the amount of natural/semi-natural habitat in the broader landscape) and landscape transformation (the amount of habitat loss to afforestation in the immediate surroundings) were measured. Habitat quality was found to be the most important for the presence of flower visitors and facilitating plant-pollinator interactions. Isolation and landscape transformation played smaller roles and often had interactive effects on plant-pollinator biodiversity. I also investigated the functional traits of flowering plants and flower visitors to understand the traits that underpin the interactions observed. Flower visitor functional dispersion and dissimilarity were most affected by environmental conditions and the interactions between seasonality and landscape variables. However, again local environmental conditions were the main variable affecting flower visitor presence and functional dispersion and dissimilarity. Season, isolation, and landscape transformation also had individual and interactive effects on flower visitor and flowering plant assemblage composition along with environmental variables. Although landscape transformation and season had limited effects on flower visitor functional dissimilarity and dispersion, flower visitor traits differed distinctly between high and low levels of landscape transformation and season. Flowering plant traits also displayed some differences between season and landscape transformation, but these were not as distinct as with flower visitors. Low levels of isolation were found to be beneficial to plant- pollinator biodiversity even under high landscape transformation. In conclusion, landscape transformation had negative effects on flowering plant and flower visitor biodiversity, but conservation corridors helped ameliorate these effects. Habitat quality and condition (here vegetation height was used as a proxy for grassland condition) were most important for the presence of flower visitors and facilitating interactions between flower visitors and flowering plants. Results suggest that corridors are providing connectivity and habitat for flower visitors due to the diverse flower visitor traits found in different landscape contexts, however, isolation still negatively impacts biodiversity in some areas. Conservation efforts should focus mainly on improving habitat quality for flower visitors. This entails the effective control of invasive plants within corridors, the introduction of appropriate indigenous flora, and establishing appropriate disturbance regimes. Achieving connectivity should still be a focus of management to allow for rescue effects in the event of species loss, however, this should not overshadow habitat quality management.
- ItemInvestigating the use of Marigolds (Tagetes spp.) and brassicaceous cover crops as a tool for the management of lesion nematodes (Pratylenchus spp.) in apple orchards(Stellenbosch : Stellenbosch University, 2024-03) Fourie, Louis Welricht; Knoetze, Rinus; Stokwe, Nomakholwa Faith; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The global surge in conscious consumerism favouring organically grown produce with minimal environmental impact has placed a considerable strain on global agriculture, particularly in fruit production which is heavily reliant on agrochemicals in crop protection programs. Fruit producers are expected to withdraw agrochemicals from crop protection programs to meet the demand for organically grown produce. Additionally, increasingly stringent maximum residue levels (MRLs) set by global export markets on agrochemical residue intensify the need for alternative crop protection solutions. Motivated by the drive towards organic produce, in this study, we evaluated the use of cover crops as an alternative control measure to chemical soil fumigation and the use of nematicides against the most prevalent nematode pest in South African apple orchards – the root lesion nematode (RLN) (Pratylenchus hippeastri). Two marigolds (Tagetes spp.) the African marigold (T. erecta) and the French marigold (T. patula) and three brassicaceous cover crops, brown mustard (Brassica juncea), Ethiopian mustard (Brassica carinata) and white mustard (Sinapis alba) were tested, through pot trials, for their ability to suppress RLN in infested orchard soil and inside the roots of infested apple trees. The suppressive potential of these cover crops was tested in three ways; (1) grown as a cover crop, (2) used as a soil amendment for biofumigation and (3) used as a soil amendment in combination with soil solarization (biodisinfestation). Along with this, a pilot trial was performed in a commercial apple orchard in Grabouw, Western Cape, South Africa (SA), where we evaluated the potential of marigolds to establish, grow, and suppress RLN in the soil and in the roots of apple trees under the conditions of a commercial apple orchard. Five inoculation methods were tried to obtain soil infested with RLN. Infested orchard soil in combination with infested apple root fragments proved to be most effective. However, this study emphasizes the need for an optimal growth medium which supports RLN survival while maintaining sterility for accurate experimental results. Cover crops used in these experiments are not conducive hosts to RLN. Marigolds, acting as cover crops, effectively reduce RLN populations in the soil through the release of an allelopathic root exudate, α-terthienyl. Conversely, brassicaceous cover crops do not impact RLN populations unless utilized for biofumigation. Biodisinfestation exhibits an enhanced level of RLN control in the soil as well as inside the apple roots consequently suppressing overall RLN reproduction. The success of biofumigation and biodisinfestation greatly depends on conducive climatic conditions (Adequate soil moisture, sufficient oxygen, and soil temperatures between 25°C – 35°C). Marigolds have the potential to serve as RLN-suppressing cover crops in commercial apple orchards. This study provides comprehensive evidence supporting the use of these cover crops as a tool for RLN management in apple orchards.
- ItemInvestigations into the ecology and management of the polyphagous shot hole borer beetle (PSHB, Euwallacea fornicatus) in South Africa(Stellenbosch : Stellenbosch University, 2023-12) Roberts, Elise; Roets, Francois; Paap, Trudy; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: The polyphagous shot hole borer beetle (PSHB) (Euwallacea fornicatus) (Coleoptera: Curculionidae: Scolytinae) and its primary fungal symbiont, Fusarium euwallaceae, is a pest-disease complex that has killed a wide range of tree species in multiple countries on six continents, including South Africa. As with any invasive pest, monitoring programmes reveal the drivers behind species population dynamics in invaded regions, which helps to mitigate potential impacts and inform management strategies. This study involved a 26- month monitoring programme in an urban-agricultural fringe setting of the Western Cape province, South Africa. Baited traps were used to determine activity patterns in comparison with temperature, as well as infestation dynamics over time in comparison with climatic and biological factors. Results suggest that activity is strongly temperature dependent, and numbers peak in late summer. The number of surrounding infested reproductive hosts was an important explanatory variable for increasing beetle abundance and infestation levels, while focal tree infestation “saturation”, tree stress and tree size may also play a role. Infested host tree removal may be important for agricultural areas where crops are surrounded by reproductive hosts either deliberately planted as windbreaks or growing naturally. Two prominent management strategies for invasive forest pests were trialled: tree removal and therapeutic chemical treatment. Results suggest that tree removal and appropriate disposal of infested wood can decrease local propagule pressure, especially if conducted in colder months. Furthermore, some therapeutic chemical treatments reduced fungal growth, number of new PSHB attacks, and beetle colony success, but control was never completely successful. These results indicate that a combination of physical and chemical control options may help to reduce propagule pressure, but is unlikely to prevent infestations for long periods.
- ItemAlternative pest control methods for false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae): exploring juvenile hormone analogs and entomopathogenic nematodes for integrated pest management(Stellenbosch : Stellenbosch University, 2023-03) Viljoen, Nadia; Karsten, Minette; Terblanche, John; Stokwe, Nomakholwa; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: False codling moth (FCM) (Thaumatotibia leucotreta (Meyrick, 1913), Lepidoptera: Tortricidae) is a major phytosanitary pest of diverse crops in southern Africa, especially deciduous fruit and citrus. Here, I provide an overview of the significance of FCM in a South African context, a brief overview of current pre- and post-harvest control methods, and the factors contributing to the increased pressure towards alternative, pesticide-limited control. False codling moth control is currently reliant on integrated pest management (IPM) that employs multiple strategies in combination. To assess the potential inclusion of juvenile hormone analogs (JHA), fenoxycarb and methoprene, into current IPM programmes and/ or Sterile Insect Technique (SIT) programmes I investigated their effect on the development, cold stress resistance and flight performance in false codling moth under different constant temperatures in two experiments. In a third experiment, the concept of adding additional stressors to the system was investigated, by assessing the interaction of methoprene and fenoxycarb with a heat wave exposure on the susceptibility of FCM to the entomopathogenic nematode, Steinernema yirgalemense Nguyen, Tesfamariam, Gozel, Gaugler and Adams (Rhabditida: Steinernematidae). In the first experiment, I exposed fourth to fifth instar larvae to four concentrations of fenoxycarb and methoprene at 25 °C: 0.1 µg/µL, 1 µg/µL, 5 µg/µL and 10 µg/µL and compared these to a handling control. Larval and pupal development time, number of pupae formed, number of adults eclosed, and longevity were recorded daily. In adults that emerged, I also tested chill coma recovery time and spontaneous behaviour as a measure of low temperature stress resistance. At 25 °C (Experiment 1), both fenoxycarb and methoprene-exposed larvae had significantly lower pupation and emergence numbers compared to the control group, and overall mixed or weak effects on development, and no effect on longevity. Low temperature performance was not affected by either methoprene or fenoxycarb at 25 °C. Next (Experiment 2), to explore the impact of temperature on JHA effects, I exposed fourth to fifth instar larvae to either 1 µg/µL methoprene or 0.1 µg/µL fenoxycarb and maintained larvae under either 20 °C, 25 °C or 30 °C while recording the same parameters as described previously (Experiment 1), with the addition of flight performance tests in adults. Cooler temperatures significantly slowed development time from larvae to adults in both treated and control groups, and reduced the number of pupae in the fenoxycarb treated group. Adult emergence was reduced by methoprene at 30 °C, and by fenoxycarb at all temperatures. Temperature afffected chill coma recovery time and sponateous behaviour in fenoxycarb-treated individuals, with larvae kept at 20 °C having a faster response time than fenoxycarb-treated FCM at 25 °C and 30°C, as well as the control group at 30 °C. Temperature also increased response time for spontaneous behaviour at 30 °C compared to 20 °C and 25 °C. Temperature, but not JHA treatments, affected the flight ability of moths, with larvae kept at 30 °C producing significantly more dispersers compared to larvae kept at 25 °C. For the third experiment, fourth to fifth instar FCM larvae were exposed to a heat wave (38 °C) for two hours, allowed to recover at 25 °C for six hours, treated with either 1 µg/µL methoprene or 0.1 µg/µL fenoxycarb, and inoculated individually with 50 IJs/50 µL of in-vitro cultured entomopathogenic nematode (EPN) S. yirgalemense. Mortality was determined after 48 hours and dissections were carried out to verify infection performed after another 24 hours. Heat wave exposure did not significantly affect EPN susceptibility for either of the JHA treated groups. Infection was much lower than expected, based on the virulence of S. yirgalemense on FCM, and additional work is needed to form a better understanding of all the contributing factors. Overall, JHA had largely predictable and pronounced negative effects on life history traits and performance in false codling moth, making it a potential addition to integrated pest management programmes as a larvicide, but would not be beneficial to SIT mass-rearing programmes. Further research into the practicality of field application of JHA is essential, as well as the role of multiple simultaneous stressors (e.g., temperature and JHA) on the efficacy of biological control agents in the field.