Evaluating baculovirus mixtures against false codling moth Thaumatotibia leucotreta Meyrick. (Lepidoptera: Tortricidae)
- Authors: Tole, Siviwe
- Date: 2024-10-11
- Subjects: False codling moth Biological control , Baculoviruses , Integrated pest management , Natural pesticides , Granulovirus
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/463996 , vital:76464
- Description: False codling moth (FCM), Thaumatotibia leucotreta, is an important pest of citrus, stone fruit, avocados, peppers, and other important agricultural crops in southern Africa. Baculovirus-based biopesticides are components in an integrated pest management (IPM) programme to manage the pest in the field. Cryptogran™ and Cryptex™ which are CrleGV-SA based-biopesticides have been effective in the control of T. leucotreta for the past 15 years. Recently, CrpeNPV-based Multimax™ and Codlmax™ have been commercialised to control T. leucotreta and other important agricultural pests. Despite these viruses being relatively host-specific and safe to humans and animals in comparison to chemical insecticides, their application is hindered by their slow speed of kill, sensitivity to UV light, and the potential for insect resistance. Research investigating the effects of mixed baculoviral interactions against target pests has been a growing field of interest due to their potential to overcome such shortcomings. Previous studies using a combination of CrleGV-SA and CrpeNPV against T. leucotreta observed a reduction in lethal concentration in laboratory bioassays, indicating that such mixtures may have the potential for application in the field. This has led to the motivation to investigate further interactions between CrleGV-SA in combination with CrpeNPV, CpGV-M, and HearNPV-Au to understand better how these viruses interact and to determine whether synergistic, additive, or antagonistic interactions can occur against T. leucotreta. The outcome of these interactions will inform researchers and farmers about best practices concerning these viruses should they be combined against T. leucotreta in the future. Prior to performing mixed baculovirus infections in laboratory bioassays, oligonucleotides targeting unique regions in the viral genomes of CrleGV-SA, CrpeNPV, CpGV-M, and HearNPV-Au were designed using Primer-BLAST. The specificity of these oligonucleotides was further tested in silico using Geneious R11 software (11.1.5). The stocks of CrpeNPV, CpGV-M, and HearNPV-Au were purified using crude OB extraction from diseased C. peltastica, C. pomonella, and H. armigera larval cadavers provided by River Bioscience (Pty) Ltd (Gqeberha, South Africa). The stock of CrleGV-SA was purified using crude OB extraction from infected T. leucotreta cadavers. Subsequently, the unique oligonucleotides were used in PCR assays to detect if the samples contained the baculoviruses of interest. Amplicons of the expected sizes were generated indicating the presence of CrleGV-SA, CrpeNPV, CpGV-M, and HearNPV-Au in each of the samples. The OBs were counted using darkfield microscopy and a counting chamber before the single and mixed infections were initiated against T. leucotreta neonate larvae. Surface-dose biological assays were used to evaluate the relative virulence in terms of lethal concentration of CrleGV-SA, CrpeNPV, and CpGV-M, alone against T. leucotreta. After 7 days, the dose mortality data was analysed using “drc” in R studio and the LC50 and LC90 were compared amongst each virus. The CrleGV-SA treatment was estimated to be the most virulent in comparison to CrpeNPV and CpGV-M. A dose discriminate assay confirmed that HearNPV does not cause mortality in T. leucotreta. Similarly, the relative virulence in terms of lethal concentration of CrleGV-SA in various ratios in combination with CrpeNPV, CpGV-M, and HearNPV-Au was determined using 7-day surface dose biological assays. The CrleGV/CrpeNPV was the most virulent mixture with lower LC50 and LC90 values measured in comparison to CrleGV/CpGV and CrleGV/HearNPV, respectively. The Tammes Bakuniak graphic method confirmed the CrleGV/CrpeNPV, CrleGV/CpGV, and CrleGV/HearNPV mixtures to be antagonistic against T. leucotreta neonate larvae in terms of lethal concentration. The last aspect of the study was to determine the probable cause of larval death. A modified CTAB protocol was used to extract genomic DNA from neonate-sized T. leucotreta cadavers collected in single and mixed infection assays. The gDNA served as templates in PCR assays using the unique oligonucleotides. In single infections, the presence of CrleGV-SA in CrpeNPV and HearNPV inoculated larvae was observed. The results suggest possible covert infections of CrleGV-SA in the T. leucotreta colony which may be caused by virus infection or an unknown stress factor. The results from the mixed infections showed the presence of each virus in all replicates except for the CrleGV/CpGV and CrleGV/HearNPV mixtures. In the CrleGV/CpGV mixture, only CrleGV-SA was present in the last replicate, suggesting a possible competition for host resources. In the CrleGV/HearNPV mixture, only CrleGV-SA was detected in all 3 replicates, suggesting that HearNPV did not have any effect and the larvae died of the CrleGV-SA infection. This is the first study to report mixtures of CrleGV-SA in combination with CpGV-M and HearNPV-Au against T. leucotreta neonate larvae. Despite the antagonistic interactions observed in the evaluated mixtures, this study has laid a foundation to further investigate how these viruses interact in dual infections for the improved control of T. leucotreta. This may be done by evaluating different ratios and combinations of baculoviruses to those used in this study. , Thesis (MSc) -- Faculty of Science, Biochemistry, Microbiology & Bioinformatics, 2024
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- Date Issued: 2024-10-11
Disaster risk management issues in WASH in South Africa: an examination of selected challenges and development of possible solutions
- Authors: Madikizela, Phindile
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/431520 , vital:72782
- Description: Access restricted. Expected release date 2025. , Thesis (PhD) -- Faculty of Pharmacy, Pharmacy, 2023
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- Date Issued: 2023-10-13
The potential of social learning to upscale the Community Based Water Quality Management (CBWQM) process: A case study of the Mpophomeni and Baynespruit Enviro Champs project
- Authors: Sithole, Nkosingithandile
- Date: 2023-10-13
- Subjects: Community of practice , Social learning , Water quality management South Africa Pietermaritzburg Citizen participation , Citizen science , Water quality South Africa Pietermaritzburg
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/402966 , vital:69910
- Description: Water is an essential component of human survival, with a wide variety of uses such as washing, cooking, drinking and growing food. Covering approximately 70% of the Earth’s surface, water is necessary for all human survival, and is a source of life for plants and animals. Only 0.036% of freshwater can be accessed and utilised by humans, which is not enough to support the rapidly growing population and economic development. This water is further exhausted by pollution caused by sewage leaks, littering, agricultural runoff and industry discharge which deteriorate water quality significantly. To exacerbate these water issues, the major issue of water accessibility is not directly linked to quantity but has been primarily attributed to poor water governance, at a global and local level (in South Africa). Poorly maintained water infrastructure and inadequate cooperative governance have resulted in the establishment of many Community Based Water Quality Management (CBWQM) projects in South Africa, to respond to water quality monitoring and management challenges. The aim of this study was firstly, to investigate how social learning was occurring within two CBWQM Communities of Practice (CoPs) located in KwaZulu-Natal, Pietermaritzburg, namely, the Baynespruit and the Mpophomeni Enviro Champs project (Case Study 1 and 2 respectively), and the potential of social learning to upscale CBWQM. Additionally, it sought to identify the type of support required for the scaling of social learning outcomes in CBWQM communities of practice, along two potential scaling pathways that were identified in a national study on scaling of CBWQM: Scaling Pathway 1(Policy engagement and support) and Scaling Pathway 2 (Capacity building). The research was undertaken as a qualitative case study approach, with data collected through semi-structured interviews, document, and questionnaire analysis to investigate social learning within the two selected case studies. The data was coded and indexed using a thematic analysis technique and an analytical framework as a tool to investigate how social learning was occurring in both case studies and explore the potential required to upscale it. The study found that there is an existing gap between policy and practice with regard to CBWQM support by government structures. Despite South African water policy advocating for public participation in water resource management, there has been limited support from government to support and resource CBWQM projects over a long period of time. To upscale the practice of CBWQM, the study found that capacity building and learning needs to be improved and better supported practically through models such as the 5Ts of learning, and through supporting CBWQM participants’ learning journey to establish learning pathways for them. , Thesis (MEd) -- Faculty of Education, Education, 2023
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- Date Issued: 2023-10-13
A comparative study of multiculturalism in South Africa and Canada: evaluating successes and failures.
- Authors: Anele Mngadi
- Date: 2022-12
- Subjects: Race discrimination -- Economic aspects – South Africa , Social justice -- South Africa , Xenophobia
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/59435 , vital:62114
- Description: The purpose of this study was to evaluate the successes and failures of multiculturalism in South Africa and Canada through the lens of critical multiculturalism as its theoretical frame. As Canada is widely-acknowledged as having one of the best multiculturalism policy and implementation programmes in the world, this study aimed to draw lessons from the Canadian model of multiculturalism in order to make recommendations to improve multicultural practices in South Africa. It is worth noting that multiculturalism in Canada is not perfect as government still struggles to implement inclusive and reconciliatory programmes for the previously colonised Indigenous communities. This study used a qualitative thematic analysis to enable a comparison of multiculturalism in these two countries. The findings of this study suggest that having a comprehensive multiculturalism policy is fundamental to ensure that aspirations of a socially cohesive multiculturalism are not merely philosophical, but are formulated into government policies, with guidelines for implementation through the guidance of critical multiculturalism theory. The findings of this study also suggest that the persistent racialised socio-economic inequalities in South Africa continue to undermine multiculturalism and nation-building efforts. , Thesis (MA) -- Faculty of Humanities, School of Governmental and Social Sciences, 2022
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- Date Issued: 2022-12
Exploring learners’ engagement with literacy in a book club
- Authors: Jamieson, Vuyokazi
- Date: 2022-04-08
- Subjects: Book clubs (Discussion groups) South Africa Makhanda , Literacy South Africa Makhanda , High school students Books and reading South Africa Makhanda , Books and reading South Africa Makhanda , Reading, Psychology of , Service learning South Africa Makhanda , Critical realism
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/263601 , vital:53642
- Description: This study observes the literacy engagement of a group of learners enrolled in Grades 8–10 in Nombulelo High School, a poorly-resourced school in the city of Makhanda in the Eastern Cape, South Africa. The learners participated in a book club hosted and run by St Andrew’s College, a privileged independent school, as a community engagement initiative. The idea of extending literacy engagement and engagement with written texts beyond textbooks used in schools is critical for learners with ambitions to enter higher education. Studying at a university requires a lot of reading, and if reading has not been taken up as a practice that involves more than ‘text consulting’ (Geisler, 1994) students will be unlikely to read the number of texts required of them. Studies (see Geisler, 1994 for an overview) have shown how the literacy of the university is very different to school based literacies. The assumption behind the study on which this thesis reports is that engagement with fictional texts might promote reading and bring about understandings of this activity as enjoyable and not a task only associated with schooling. The study is underpinned by a critical realist philosophy which allowed for the identification of structures and mechanisms that led to the emergence of literacy events in learners’ lives and to their experiences and observations of those events. The study was guided by the following questions: How do learners from a poorly-resourced high school engage around fictional texts in the context of a book club? What enables or constrains this engagement? The study was impacted by the Covid-19 pandemic in that lockdown requirements meant that learners from St Andrew’s College could not participate in the book club as much as anticipated initially as they had been forced to return home to pursue online learning. Learners from Nombuelo High School were, however, granted access to College premises, where they met in the school library following strict Covid protocols. The study draws on in-depth interviews, observations and document analysis of five learners from Nombulelo High School who participated in the book club, as well as on book reviews they wrote for the book club website. The critical realist analysis allows for the identification of mechanisms in learners’ homes and communities that enable literacies, including those that are screen-based such as using a computer, mobile phones and other technologies. This study found evidence of challenges regarding school based texts, reading fictional texts and viewing it as an enrichment of the school project. Because of children were African the emergence of communal practices and story telling is woven throughout the results section. However, is an example of the complexity of social and economic challenges facing South African marginalised schools. , Thesis (MEd) -- Faculty of Education, Centre for Higher Education Research, 2022
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- Date Issued: 2022-04-08
Service dogs for Autism Spectrum Disorder: the experiences of caregivers in South Africa
- Authors: Martin, Emma Jeanne
- Date: 2022-04-07
- Subjects: Autism spectrum disorders South Africa , Service dogs South Africa , Animals Therapeutic use South Africa , Caregivers South Africa , Animals Therapeutic use Public opinion , Animal welfare South Africa , Children with autism spectrum disorders South Africa
- Language: English
- Type: Master's thesis , text
- Identifier: http://hdl.handle.net/10962/232855 , vital:50032
- Description: Autism spectrum disorder (ASD) is a neurodevelopmental disorder, most frequently diagnosed in childhood, with symptoms including deficits in social communication and interaction as well as restricted, repetitive patterns of behaviours, interests and activities. There is no known cure for ASD, with current treatment methods focussing upon reducing symptom severity. One such treatment method is the use of autism service dogs. Internationally, autism service dogs have been available for over two decades, while in South Africa they have only been available since 2015. A fair amount of internationally published data is available on autism service dogs, however, at the time of this research study, no data was available within South Africa. This study aimed to provide a baseline for research on autism service dogs within South Africa, by documenting the experiences of caregivers whose ASD children had been supplied with autism service dogs, with regard to the uses, effects, accessibility and public perception of the autism service dogs, as well as recommendations for future improvements of autism service dogs within South Africa. Lastly, inquiry into the welfare of the autism service dogs was sought. This study was qualitative in nature, with eight families who had been supplied with autism service dogs having chosen to participate. Data collection was achieved through one semi-structured interview with each family, which was then transcribed and thematically analysed using a hermeneutic phenomenological approach. Results indicated that autism service dogs were perceived as generally accessible, useful and beneficial for ASD children and their caregivers in a variety of ways, however, they were not without their challenges, with lifestyle adjustments and public perception being especially problematic. Participants also noted recommendations for possible future improvements. Lastly, welfare concerns for the autism service dogs relating to violent behaviour exhibited by ASD children was identified, raising the question of the suitability of service dogs for the ASD population. , Thesis (MA) -- Humanities, Psychology, 2022
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- Date Issued: 2022-04-07
Statistical and Mathematical Learning: an application to fraud detection and prevention
- Authors: Hamlomo, Sisipho
- Date: 2022-04-06
- Subjects: Credit card fraud , Bootstrap (Statistics) , Support vector machines , Neural networks (Computer science) , Decision trees , Machine learning , Cross-validation , Imbalanced data
- Language: English
- Type: Master's thesis , text
- Identifier: http://hdl.handle.net/10962/233795 , vital:50128
- Description: Credit card fraud is an ever-growing problem. There has been a rapid increase in the rate of fraudulent activities in recent years resulting in a considerable loss to several organizations, companies, and government agencies. Many researchers have focused on detecting fraudulent behaviours early using advanced machine learning techniques. However, credit card fraud detection is not a straightforward task since fraudulent behaviours usually differ for each attempt and the dataset is highly imbalanced, that is, the frequency of non-fraudulent cases outnumbers the frequency of fraudulent cases. In the case of the European credit card dataset, we have a ratio of approximately one fraudulent case to five hundred and seventy-eight non-fraudulent cases. Different methods were implemented to overcome this problem, namely random undersampling, one-sided sampling, SMOTE combined with Tomek links and parameter tuning. Predictive classifiers, namely logistic regression, decision trees, k-nearest neighbour, support vector machine and multilayer perceptrons, are applied to predict if a transaction is fraudulent or non-fraudulent. The model's performance is evaluated based on recall, precision, F1-score, the area under receiver operating characteristics curve, geometric mean and Matthew correlation coefficient. The results showed that the logistic regression classifier performed better than other classifiers except when the dataset was oversampled. , Thesis (MSc) -- Faculty of Science, Statistics, 2022
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- Date Issued: 2022-04-06
Thicket expansion in a vachellia karroo-dominated landscape and its effect on herbaceous communities
- Authors: Khoza, Marina Rindzani
- Date: 2022-04-06
- Subjects: Savanna ecology South Africa , Forbs South Africa , Grasslands South Africa , Herbaceous plants South Africa , Vegetation dynamics South Africa , Forest canopies South Africa
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/291015 , vital:56808
- Description: Grass and forb species found in savannas are highly diverse, contributing to the structure and function of the savanna system. Where mean annual rainfall is seasonal and high enough to support closed canopy vegetation such as forests or thickets, savannas can exist as an alternative stable state maintained by disturbances such as fire and browsing. Biotic and abiotic processes act on savanna and forest (or thicket) systems maintaining both their tree and herbaceous cover at levels that ensure their persistence in those states. Studies have shown that many semi-arid rangelands in South Africa have undergone a rapid increase in tree cover (of both native and non-native species) over the past several decades. This process of increasing tree cover in semi-arid savannas, termed bush encroachment, results in a biome shift, changing landscapes that were once grasslands with few trees to ones dominated by broad-leaved trees with fewer sun-adapted forbs and grasses. The aim of this study was to investigate the impact of changing woody cover and its associated changes in tree composition, tree canopy structure, light dynamics in the understory and herbaceous community composition on Endwell farm in the Eastern Cape. Canopy cover changes between the years 1949 and 2019 were analysed at 51 sites on the farm and related to historical rainfall patterns. There had been a general increase in tree cover over the past several decades on the farm, and many sites showed a change from open (0-15%) in 1949 to low (1635%), moderate (36-50%) and high (51-100%) canopy cover in 2019. In earlier years most sites had a canopy cover below 50%, and the higher canopy cover values (>65%) occurred in more recent decades. Canopy cover of ~ 50% was found to be rare in each decade. This suggests that ~50% canopy cover maybe a transient, unstable state. The period with the highest rate of canopy cover increase was 2002-2013, and this increase coincided with a high mean annual rainfall 10 years prior to 2002 and a high mean annual rainfall in most years between the 20022013 period. The period between 2002 and 2013 also had the highest number of sites transitioning from lower to higher tree canopy cover classes, indicating that rainfall may have been a factor driving bush encroachment during the past several decades. An increase in canopy cover (a decrease in light transmittance) was accompanied by changes in woody species composition during thicket formation. The low canopy cover (high light transmittance) sites were dominated by Vachellia karroo and Scutia myrtina trees, while high tree cover sites had fewer V. karroo and S. myrtina trees and were rather characterised by an abundance of thicket tree species. Species proportion, NMDS and dendrogram plots indicated that sites with a light transmittance range between 50-100% had similar tree species compositions, different from sites with light transmittances <50%. An increase in tree density was strongly correlated to an increase in canopy cover (from 2019 satellite imagery), density of trees > 3m, maximum height reached by trees, diversity of trees, total canopy volume, total canopy area and leaf area index (LAI), and a decrease in light transmittance. A structural equation model (SEM) was used to explore the relationships between canopy characteristics (maximum canopy area, canopy volume, tree diversity, density of trees, density of trees >3m, individual trees and maximum canopy height), aerial canopy cover in 2019, and light transmittance. The model explained 73% of the variation in light transmittance, mostly via the direct effect of canopy characteristics. Canopy characteristics had a strong influence on both aerial cover in 2019 and directly on light transmittance, but canopy cover in 2019 had a weak influence on light transmittance. The herbaceous layer was rich and dominated by C4 grasses such as Eragrostis plana, Sporobolus fimbriatus, Themeda triandra and Digitaria eriantha) and forbs including Hibiscus aethiopicus, Helichrysum dregeanum, Helichrysum nudifolium and Gerbera viridifolia at low canopy cover sites with high light transmittance. In contrast, high tree cover sites had fewer herbaceous species in general. Grass and forb species characteristic of these sites high canopy cover sites were Panicum maximum, Loudetia flavida, Pellaea viridis and Cyperus spp. Different sites with low light transmittance (<50%) had similar herbaceous species composition. Basal cover, richness, abundance and diversity of herbaceous plants decreased significantly with an increase in tree density, density of trees >3 m, canopy volume, canopy area, canopy cover, LAI, and increased significantly with increasing light transmittance. Most grasses had their highest densities at LAI <0.5, which was estimated to correspond to ~75% light transmittance and ~38% canopy cover and then started to decline thereafter. Herbaceous species basal cover was also highest at LAI <0.5. An SEM model indicated that herbaceous diversity, basal cover and richness responded both to light availability and to the structure of the woody vegetation directly (R2 = 0.53). While the effect of light transmittance on herbaceous communities was strong (0.41), there was little difference between the effect of light transmittance and canopy characteristics (-0.35) on herbaceous communities. Two possible threshold points, relating to two types of transitions in vegetation structure, could be deduced from this study. The first threshold occurred at canopy cover ~ 40% (LAI < ~ 0.5, light transmittance ~ 75%), at which point many of the common herbaceous species, including the dominant C4 grasses, began to decline in abundance while the composition remained characteristic of the savanna state. A canopy cover of less than ~ 40% at a site provides a suitable state for a high abundance of grass and forb species which help maintain an open system by facilitating fires. The second threshold marked a compositional shift between savanna and closed-canopy vegetation states. Savanna species (trees, grasses and forbs) dominated at high light transmittances (>50%) and were significantly reduced at low light transmittances (< 50%), indicating a possible species composition threshold at ~50% light transmittance at which a savanna state switches to a thicket (LAI ~ 1 and canopy cover ~70%). This point indicated the point where there was a significant difference in both tree and herbaceous plant compositions, with a marked reduction in the occurrence of C4 grasses at light transmittance <50%. Fire is supressed when the C4 grass layer is lost, and further thicket encroachment will take place causing complete canopy closure. Land managers in this system should start becoming concerned about a reduction in grass biomass when canopy cover reaches about 40% and would have to reduce tree cover before the threshold of 50% light transmittance (70% canopy cover from aerial photos) is reached to maintain a savanna system. , Thesis (MSc) -- Faculty of Science, Botany, 2022
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- Date Issued: 2022-04-06
Protean career management of independent music creatives in Gqeberha : narratives of practice
- Authors: Henneberry, Robyn
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54439 , vital:46541
- Description: This study is concerned with the promotion of local music creatives. The literature explores ways to help the independent music creatives successfully navigate in the music industry by adopting a protean career profile. The research question that was explored in the study was whether or not the independent popular female creatives in the city of Gqeberha’s music industry adopted protean career profiles for successful career navigation. These pop music creatives’ profiles were compared to those of classical creatives for further insight. Relevant literature was analysed to collect data about what international authors have discovered about creatives’ successful navigation of their careers. The information that was gleaned from the analysis indicated that numerous individuals have adopted the profile of the protean career to successfully navigate their environment. The rationale for adopting the protean career profile was that it is directly related to one’s employability. Although the working world (including the music industry) is rapidly changing, this notion of employability will enable an individual to remain updated about the latest trends in their work environment and thus successfully navigate that environment. This concept was applied to research among music creatives in the South African (SA) context. Although there was limited research on the protean career profile, the published research findings that were available indicated that employability and information were in alliance with the international research on the protean career (which constitutes one’s employability). Employing qualitative data collection procedures, the researcher interviewed 14 independent female music creatives with different backgrounds, roles and experiences. Interviews were semi-structured one-on-one as well as focus groups. This narrative strategy of inquiry helped determine whether or not these individuals had adopted the protean career for successful navigation of their working environment. After data collection the researcher engaged in a cyclical coding process for deep analysation of the data utilising atlas.ti. The data was reduced from codes to categories, and eventually towards linking categories. The findings from the study revealed that the participants’ environment (surroundings) did not sufficiently support them, the creatives do not have sufficient guidance in their music paths and not all of them had adopted the protean profile. , Thesis (MA) -- Faculty of Humanities, School of Visual and Performing Arts, 2021
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- Date Issued: 2021-12
The biological control of Egeria densa Planch. (Hydrocharitaceae) in South Africa
- Authors: Smith, Rosali
- Date: 2021-10-29
- Subjects: Egeria (Plant genus) Biological control South Africa , Hydrocharitaceae Biological control South Africa , Aquatic weeds Biological control South Africa , Leafminers South Africa , Plant invasions South Africa , Resilience (Ecology) South Africa , Freshwater ecology South Africa , Hydrellia South Africa , Submerged macrophyte
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191102 , vital:45060 , 10.21504/10962/191102
- Description: Over the last thirty years, biological control, the use of host-specific natural enemies, has been a huge asset in the management exotic aquatic macrophytes such as Pistia stratiotes L. (Araceae), Pontederia crassipes Mart. (Solms) (Pontederiaceae), Azolla filiculoides Lam. (Azollaceae), Salvinia molesta D.S. Mitch (Salviniaceae) and Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), also known as the “Big Bad Five” in South Africa. Despite these successes, freshwater ecosystems in South Africa have been harder to restore to an invasive macrophyte-free space, due to chronic disturbances such eutrophication, propagule dispersal and hydrological alterations. In the Anthropocene, where human activities have profound effects on their environment, these disturbances weakens ecological resilience and drive aquatic plant invasions. Due to long periods of invasions and the presence of a new suite of exotic aquatic plant propagules, native vegetation recolonization has been slow or even absent. Instead, the release of resources, such as sunlight, nutrient and space through aquatic weed management acts as a catalyst for secondary biological invasion. New invasive aquatic weeds include submerged and rooted emergent growth types, with Egeria densa Planch. (Hydrocharitaceae) the most widely distributed submerged aquatic weed in South Africa. It can quickly form dense monoculture stands that have ecological, economic and social impacts. Because of its ability to regenerate from plant fragments with double nodes, mechanical control is inappropriate. Additionally, mechanical and chemical control not only affects E. densa but have significant non-target effects. In response to its rapid spread over the last 20 years, especially following floating invasive aquatic management, a biological control programme was initiated, and in 2018, the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was released. This was the first release of a biological control agent against E. densa in the world, and the first agent released against a submerged aquatic weed in South Africa. This thesis comprises the subsequent step of a biological control program when permission for the release of an agent have been obtained. A brief history of macrophyte invasions in South Africa’s unique freshwater systems are given in the literature review. Contributing factors to secondary invasions within the context of ecological resilience are introduced. An argument for the benefit of biological control as nuisance control is given, especially because E. densa and its natural enemy, H. egeriae is the focus species of this thesis. The main goal after permission for the release of an agent have been obtained, is to establish and build-up field populations. Research questions in this thesis aimed to investigate factors that contribute to or negate this goal. Through laboratory and field experiments we investigated the thermal physiology of the agent, and its climatic suitability to its novel range; different release strategies on field establishment and biotic resistance through the acquisition of novel parasitoids. Considering the longevity of this biological control program, we investigated the effects of elevated CO2 on the interaction between E. densa and H. egeriae through open top chamber experiments. Laboratory thermal physiology results showed that the agent is able to survive, develop and proliferate at all E. densa sites throughout the year. This is confirmed with the establishment of the agent at two release sites, the Nahoon River in the Eastern Cape Province and the Midmar Dam in KwaZulu-Natal. Post-release surveys showed that H. egeriae requires augmentative releases to sustain field populations. Without augmentative releases, H. egeriae herbivory levels were almost negligent. However, a contributing factor to low field-populations was parasitism. The biological control agent acquired three parasitoids, which have previously been described from Hydrellia lagarosiphon Deeming (Diptera: Ephydridae), a specific herbivore to Lagarosiphon major (Ridl.) Moss (Hydrocharitaceae). These results provide information on the immediate establishment and effectiveness of the H. egeriae. Results from the elevated CO2 study suggest that E. densa will become less nutritious through a shift in leaf C/N ratio, when ambient 800ppm is bubbled into experimental growth chambers. Hydrellia egeriae feeding was affected by ambient CO2 levels and plant nutrient availability. The set levels of ambient CO2 levels used in this experiment produced dissolved inorganic carbon levels that were lower than dissolved inorganic carbon levels in E. densa invaded sites. This suggests that, submerged aquatic plant-insect interactions may be harder to predict from only laboratory experiments. Further investigations are necessary to establish system-specific characteristics i.e. dissolved inorganic carbon and target plant nutritional quality. The biological control of E. densa in South Africa is still in its infancy. This study presents results from post-release surveys up until two years after the agent was released. From this study, Hydrellia egeriae exhibits the potential to be an effective biological control agent, but release strategies should be adapted to sustain field populations and to limit field parasitism effects. Continued post-release surveys will provide a more comprehensive idea of the seasonal fluctuations of field-populations and parasitism. Surveys at multiple sites will provide information on potential site specific characteristics that contribute to or negate biological effort. Considering the high nutrient status of South African freshwater systems, a more holistic approach to E. densa management is necessary. This will require the strengthening of ecological resilience to prevent systems from shifting into an alternate invasive stable state. In addition, aquatic weed management needs to be addressed by a resilient social network, which ultimately calls for the strengthening of socio-ecological resilience. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
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- Date Issued: 2021-10-29
An assessment of the wild cyclopia subternata (vleitee) resource
- Authors: Van der Walt, Wouter
- Date: 2021-04
- Subjects: Legumes -- South Africa , Fynbos -- South Africa , Fynbos ecology -- South Africa , Fynbos -- Harvesting -- South Africa , Biodiversity conservation -- South Africa , Traditional ecological knowledge -- South Africa , Wild Cyclopia Subternata (Vleitee) , Honeybush tea industry
- Language: English
- Type: thesis , text , Masters , MSc
- Identifier: http://hdl.handle.net/10962/176874 , vital:42767
- Description: Cyclopia spp. is used for the production of Honeybush tea, an herbal tea which is used in many cases as a substitute for rooibos tea. The wild harvesting of this fynbos plant still brings in up to 85% of the annual crop and as such needs to be carefully monitored in order to avoid over harvesting and the destruction of biodiversity within the Eastern and Western Cape mountain regions of Southern Africa. Due to the concerns of overharvesting and unsuitable use of the wild resource issues of supply security have been raised. There is a lack of formal knowledge relating to the plant, its harvesting, the industry and its economic potential. This study aimed to amend this scarcity by contributing to the knowledge of C. subternata as a wild harvested plant, the physical environment favoured by C. subternata, sustainable use through harvesting of the wild plant and harvesting methods specific to this honeybush species. The research concludes by presenting a guideline for best harvest practices of the wild C. subternata plant. , Thesis (MSc) -- Faculty of Science, Department of Geography, 2021
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- Date Issued: 2021-04
Evaluating the potential of monometallic and bimetallic nanomaterials as horseradish peroxidase mimetics
- Authors: Mvango, Sindisiwe
- Date: 2017
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65134 , vital:28694
- Description: This study presents the synthesis of citrate-capped gold nanoparticles (cit-AuNPs), copper oxide nanoparticles (CuONPs), glutathione-capped gold nanoparticles (GSH-AuNPs), 4- aminothiophenol-capped gold nanoparticles (4-ATP-AuNPs), 4-mercapto benzoic acid- capped gold nanoparticles (4-MBA-AuNPs) and copper oxide gold nanoalloys (CuO-Au nanoalloys). Microscopy and spectroscopy techniques were used to confirm the successful synthesis of these nanoparticles. The synthesized nanoparticles were studied their potential applications as horseradish peroxidase (HPR) enzyme mimetics and for the detection of glucose. The cit-AuNPs and GSH-AuNPs exhibited peroxidase-like activity towards hydrogen peroxide (H2O2) with high Michaelis-Menten (Km) values of 61.5 mM and 30.8 mM, respectively. The other nanoparticles, that is, 4-ATP-AuNPs, CuONPs and CuO-Au nanoalloys gave lower Km values of 4.74 mM, 1.92 mM and 4.05 mM, respectively. The obtained Km values were comparable to those of HRP enzymes which ranged from 0.214 - 3.70 mM with 4-ATP-AuNPs and CuO-Au nanoalloys slightly higher. These values were within the reasonable experimental values of the HRP enzyme. The studies showed that the gold nanoparticles had low adsorptive efficiency towards H2O2 compared to the copper-based nanoparticles (CuONPs and CuO-Au nanoalloys). The CuO-Au nanoalloys also showed the synergistic effect between the gold and copper nanoparticles with extended linear concentration range for the quantification of H2O2. The mechanism of catalysis was confirmed using UV-vis spectroscopy and electron paramagnetic resonance (EPR) in that the generation of reactive oxygen species was observed. The use of 1,3-diphenylisobenzofuran (DPBF) as radical quencher and 5,5- dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger confirmed the production of reductive reactive oxygen species using UV-vis and EPR studies. The rate of production of reactive oxygen species in the gold-based nanoparticles was small compared to the copper-based nanoparticles, that is CuONPs and CuO-Au (bimetallic) nanoalloys. The synthesized nanoparticles were further studied their potential use in the colorimetric detection of glucose. The copper-based nanomaterials, CuONPs and CuO-Au nanoalloys, were excellent towards detection of glucose, with a limit of detection (LoD) of 9.34 pM for CuONPs and 6.75 pM for CuO-Au nanoalloys. The linear concentration (LCR) range of CuONPs was 0 to 70 pM and for CuO-Au nanoalloys the LCR was 0.0 - 30 pM. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
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- Date Issued: 2017