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.
- ItemEvaluating the potential biological control of Margarodes prieskaensis using South African entomopathogenic fungi, and/or entomopathogenic nematodes(Stellenbosch : Stellenbosch University, 2023-04) Erasmus, Talitha; Stokwe, Nomakholwa F.; Allsopp, Elleunorah; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.ENGLISH ABSTRACT: Margarodes prieskaensis (Jakubski) (Homoptera: Coccoidea: Margarodidae) occurs naturally in the Northern Cape, Limpopo and Mpumalanga in South Africa, where it is a serious pest on table and raisin grapes (Vitis vinifera L.) The larvae of M. prieskaensis feed on grapevine roots, causing poor growth and reduced vigor which eventually result in the death of the infested plant. Currently, there are no chemicals registered for the control of M. prieskaensis in South Africa, and no resistant rootstocks or natural enemies of M. prieskaensis have been identified to date. The aim of the study was to investigate the potential of local entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPN) to control M. prieskaensis females in table and raisin grapes. Six local EPF isolates, obtained from the Stellenbosch University collection, were screened for their pathogenicity against M. prieskaensis females under laboratory and semi-field conditions: Beauveria bassiana, Metarhizium robertsii, M. pinghaense, M. brunneum, M. majus and M. anisopliae performed the best and achieved high percentages of infection and mortality and were selected for subsequent trials. The other local EPF isolates did not perform adequately, even though infection did occur and thus warrant further investigation. Metarhizium pinghaense outcompeted M. majus in the concentration trials, especially in terms of overall infection success, however both EPF had a high infection success rate. In semi-field trials where M. majus and M. pinghaense were evaluated under optimal conditions, M. majus was outperformed by M. pinghaense, producing higher levels of mycosisi n insect cadavers. The EPF treatments showed high infection rates, while there was no infection in the untreated control. However, the efficacy of the EPF in inducing M. prieskaensis mortality could not be determined accurately due to high levels of insect mortality in the control. Field trials were conducted in the Northern Cape and Limpopo to test the efficacy of M. pinghaense to control females of M. prieskaensis. The infection rate was significantly lower than in the laboratory and semi-field trials. Moisture, temperature ranges and other environmental factors can affect the efficiency of EPF in the soil. Limpopo experienced more optimal temperatures during the trial, with an average infection rate of 28,98%. The trial site in the Northern Cape experienced harsher environmental conditions with extremely cold temperatures during the trial period, resulting in a lower infection rate of 24,61%. Solar radiation also possibly contributed to the overall lower infection rate during the field trials. Suitable formulations of EPF could possibly reduce the dire impact of environmental factors like extreme temperatures, low humidity and solar radiation. The field trials in the Northern Cape also assessed the efficacy of a local EPN species, Steinernema yirgalemense to control females of M. prieskaensis. Overall, little to no infection was achieved. Margarodes prieskaensis presents challenges to field applications of EPN and S. yirgalemense was unable to reproduce within the M. prieskaensis females, indicating that it is possible that M. prieskaensis either inhibit the symbiotic bacteria secreted by the EPN or that the females secrete repellent volatiles that preventinfestation. Before attempts are made to test other EPN species against this pest, the possibility that M. prieskaensis females can inhibit EPN infestation warrants further investigation. A combined application of S. yirgalemense and M. pinghaense was also included in the field trials. The infection rate for both the EPN (3.7%) and EPF (11.1%) was low in the combination application, with indications of antagonism between the EPF and EPN. This might explain why the infection rate for M. pinghaense was lower in the combination treatment than when applied on its own. This should be resolved before further studies with combined applications are done. This study is the first to show that females of M. prieskaensis are susceptible to infection by EPF species and that their use as biocontrol agents warrants further investigation. Male pre-pupae of M. prieskaensis spend between 30 and 50 days just underneath the soil surface before developing into pupae and should also be investigated as targets for biocontrol. It is therefore recommended that the use of EPF as a soil drench application against the pre- pupae should be investigated. This study provided crucial baseline information on the efficacy of local EPF and EPN against M. prieskaensis females. For future studies on EPF to control M. prieskaensis, it would be beneficial to resolve the problems identified in this study, including the method of collecting and handling M. prieskaensis females, and adequate formulation of EPF for protection against environmental factors.