Evaluation of potential oviposition deterrents for false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae)
- Authors: Dambuza, Khalipha
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424479 , vital:72157
- Description: There has been extensive research on the use of semiochemicals as deterrents or true repellents in insect pest management, particularly in push-pull strategies. Much of this research has focused on pests of medical and veterinary importance and has been limited for agricultural pests. This means there is an opportunity to study use of deterrents to manage pests of agricultural importance. No study has been conducted on deterrents for false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a key phytosanitary pest in citrus orchards across South Africa. This study assessed FCM oviposition deterrence in botanicals (plants (n = 11) and essential oils (n = 15)), and some commercial pesticides (n = 7) used for FCM control in South Africa. All tested botanicals were selected based on an extensive literature review of plant compounds that have been reported to deter or repel lepidopteran pests. Choice and no-choice oviposition bioassays were conducted in complete darkness in a controlled environment room. Oranges treated with solutions/suspensions of potential oviposition deterrents were placed into a cage with gravid FCM females for four hours, with oviposition being recorded every hour. Of the 33 tested compounds, only eight significantly reduced FCM oviposition (P < 0.05) compared to the control in oviposition bioassays i.e. two essential oils (lavender and peppermint), two plant crude extracts (garlic and marigold), one fruit (Mango), and three commercial FCM insecticides (Delegate, Coragen, and Warlock). All identified oviposition deterrents, except for Mango, were further investigated for their ovicidal properties in concentration response bioassays, where all botanicals were identified to have dual action (both deterrent and ovicidal properties), as they significantly (P < 0.05) reduced FCM oviposition and egg hatch. Garlic was the most efficacious botanical whilst Warlock was the only commercial insecticide that did not show ovicidal activity (F = 41.17, P = 0.0622). Larval penetration of the host fruit was less than egg hatch for all tested compounds in concentration response bioassays. Oviposition, egg hatch, and larval penetration were all affected by concentration, with the higher concentrations being the most effective. The efficacy of these deterrent compounds should be further tested in semi-field and/or field trials, and they may have potential in FCM management as allomone dispensers or sprays. They can also be implemented in push-pull strategies where they can be used in conjunction with FCM attractants. Lastly, repellence studies should be conducted in absentia of the host fruit to determine whether oviposition deterrence was a result of true repellence or odour masking. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
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- Date Issued: 2023-10-13
faces, disappearing
- Authors: Mbhele, Mbekezeli
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424952 , vital:72196
- Description: My thesis explores township life through the eyes of a young boy, Sengwayo, whose life changes when a strange man arrives unexpectedly to stay with his family. The man is introduced as his uncle but nothing further is said about him. Sengwayo soon begins to experience visions and decides to find out who this man really is. His search for truth soon becomes obsessive and culminates in tragedy. As we follow Sengwayo in his quest of uncovering the truth it becomes difficult to differentiate between Sengwayo’s imagination and reality. This thesis collapses the distance between what is and what could be. It does this by alternating short sentences mostly used in the poetry of maskanda lyrics, and in the stream of consciousness found in jazz improvisation. In literary terms, the thesis draws influence from the rants and rhyme schemes of Lesego Rampolokeng, the tone and pace of Sony Labou Tansi and the surrealism in Mangaliso Buzani’s work. , Thesis (MA) -- Faculty of Humanities, School of Languages and Literatures, 2023
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- Date Issued: 2023-10-13
M3: Mining Mini-Halos with MeerKAT
- Authors: Trehaeven, Keegan Somerset
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424754 , vital:72181
- Description: This work aims to showcase the MeerKAT telescope’s capabilities and related calibration and imaging software in studying the emission of radio mini-halos. These diffuse radio synchrotron sources surround a Brightest Cluster Galaxy (BCG) in relatively relaxed clusters out to a few 100 kpc in size. They are difficult to image because of their relatively low surface brightness and small angular size. Hence, they could not be studied in great detail by previous generations of radio telescopes and much about their nature, particularly the exact production mechanism, is not yet fully understood. Thus, for the first time, MeerKAT observed a sample of five galaxy clusters to investigate the central radio mini-halo in each. Studying these sources requires the deepest images generated from the data and the effective subtraction of any projected sources obscuring or contaminating the underlying diffuse emission. Therefore, I describe the data reduction used to create third-generation calibrated, primary beam corrected, point source subtracted Stokes I L-band continuum images of these clusters. For first- and second-generation calibration, I use the CARACal pipeline, which implements software optimised explicitly for MeerKAT data. For third-generation calibration, I use the faceted approach of killMS and DDFacet, and then I perform visibility-plane point source subtraction to disentangle the compact and diffuse emissions. I then measured the size, flux density, in-band spectral properties, and radio power of the central mini-halos. I present the first new mini-halo detection by MeerKAT (MACS J2140.2-2339, Trehaeven et al. accepted), the first spectral index maps of these mini-halos, which show very interesting distributions, and a ∼100 kpc II southern extension to the ACO 3444 mini-halo previously unseen in archival VLA data. Thereafter, I present a multi-wavelength case study for two complementary mini-halos from our sample and show via a radio-to-X-ray spatial correlation test that they might be caused by different particle (re)-acceleration mechanisms. Through these initial science results, I have shown that future observations of radio mini-halos with MeerKAT are an exciting prospect that can lead to a better understanding of the fundamental physics behind these sources. , Thesis (MSc) -- Faculty of Science, Physics and Electronics, 2023
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- Date Issued: 2023-10-13
The application of statistical classification to predict sovereign default
- Authors: Vele, Rendani
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424563 , vital:72164
- Description: When considering sovereign loans, it is imperative for a financial institution to have a good understanding of the sovereign they are transacting with. Defaults can occur if proper evaluation steps are not considered. To aid in the prediction of potential sovereign defaults, financial institutions, together with grading companies, quantify the risk associated with issuing a loan to a sovereign by developing sovereign default early warning systems (EWS). Various classification models are considered in this study to develop sovereign default EWS. These models are the binary logit, probit, Bayesian additive regression trees, and artificial neural networks. This study investigates the predictive performance of the various classification techniques. Sovereign information is not readily available, so missing data techniques are considered in order to counter the data availability issue. Sovereign defaults are rare, which results in an imbalance in the distribution of the binary dependent variable. To assess data sets with such characteristics, metrics for imbalanced data are considered for model performance comparison. From the findings, the Bayesian additive regression technique generated better results than the other techniques when considering a basic data analysis. Moreover when cross-validation was considered, the neural network technique performed best. In addition, regional models had better results than the global model when considering model predictive capability. The significance of this study is to develop sovereign default prediction models using various classification techniques focused on enhancing previous literature and analysis through the application of Bayesian additive regression trees. , Thesis (MSc) -- Faculty of Science, Statistics, 2023
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- Date Issued: 2023-10-13
The possible effect of insecticide drift from citrus orchards, and acute toxicity of insecticides on the biocontrol agents of Pontederia crassipes (Mart.) Solms-Laub (Pontederiaceae) established along citrus orchards in the Lowveld region of Mpumalanga Province, South Africa
- Authors: Mabuza, Mefika Michael
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424468 , vital:72156
- Description: This study investigated the possible effect of insecticide drift on naturalized biological control agents of Pontederia crassipes (Mart.) Solms-Laub (Pontederiaceae), in the Lowveld region of Mpumalanga Province of South Africa. Occurrence and abundance of biocontrol agents were recorded at three sites on the Crocodile River and at three dams adjacent to citrus orchards. Leaves of P. crassipes and water samples were collected for insecticide residues and also nutrient status of the water and plants. Eccritotarsus catarinensis Carvalho (Hemiptera: Miridae), Neochetina spp. (combined) (Coleoptera: Curculionidae), and Orthogalumna terebrantis Wallwork (Sarcoptiformes: Galumnidae) were recorded with notable variation in abundance between the river and dams across regions. Insecticide residues were not detected on all leaves sampled across study regions, however, nutrients were detected with nitrate ranging between oligotrophic and mesotrophic. Phosphorus was also detected, but, neither of the nutrients correlated with the occurrence and abundance of naturalized biological control agents of P. crassipes. Bioassays were conducted to measure the effect of commonly used insecticides (viz. Methomyl and Chlorpyrifos) on the survival and feeding damage of biological control agents of P. crassipes. Survival of individual insects was recorded between 0.5 and 120 hours for Megamelus scutellaris and Neochetina eichhorniae Warner (Coleoptera: Curculionidae) adults for treatments where insecticides were topically applied onto the insects or leaves were dipped into the pesticides. Concentrations below field rates, recommended and above field rates of Methomyl and Chlorpyrifos on either exposure techniques significantly reduced survival and feeding of biocontrol agents. Methomyl was more toxic compared to Chlorpyrifos and it significantly reduced the survival of M. scutellaris and N. eichhorniae. In conclusion, in this study, population abundance of biocontrol agents of P. crassipes at the Lowveld region of Mpumalanga was not influenced by pesticide drift, but, insecticides commonly used in the citrus orchards has the potential to negatively impact naturalized biological control of P. crassipes as demonstrated by the bioassays. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
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- Date Issued: 2023-10-13
The views and opinions of Rhodes University lecturers towards isiXhosa as a language of learning and teaching (LOLT) in higher education
- Authors: Nkunzi, Zintle
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424963 , vital:72197
- Description: This research sought to investigate how African languages function as a communicative tool in a university where English is the medium of instruction. The study's purpose is to provide a systematic review of research that has been carried out on language attitudes towards isiXhosa as a language of learning and teaching (LoLT) in higher education. The study reveals that South African higher education institutions such as Rhodes University mostly use English as the LoLT- a language which for most lecturers is not their first/home language but helps ease communication in a multilingual community. Rhodes University is characterised by multilingualism because the university community is made up of diversity in culture, language, and educational background of the people. Previously explored language attitude studies are based on students’ views and this study investigated RU lecturer views and opinions towards isiXhosa as a LoLT. The study focused on the importance and the need (if any) of isiXhosa in a multilingual higher education institution. The study reveal that language barriers are one of the difficulties, but academic cultural differences seem to play a crucial role that can impact on the learning and teaching outcomes. This can lead to negative experiences and the forming of stereotypical views. These views include how lecturers are and should be trained to teach mathematics, science, and academic studies in African languages. The SA higher education practices and language use (i.e., monolingual language policy) are one of the reasons that the implementation of indigenous languages in education policies in SA is fraught with difficulties due to several factors. Amongst the factors is the fact that indigenous languages are not yet fully developed as academic languages. The study further reveals that lecturers find it difficult to teach mathematical studies in isiXhosa because of lack of terminology in the language for academic purposes particularly at a tertiary level. Furthermore, existing literature highlights the importance of the use of code-switching which is a beneficial practice for lecturers in assisting their students who struggle with English as a LoLT at RU. The lecturer views towards isiXhosa as a LoLT at RU is not only on language barrier but also about the lack of development in the language use in spaces where only English is believed to be the best such as language for academics. The study also reveals an integration of Information Communication Technology in education and how language appears as a barrier. , Thesis (MA) -- Faculty of Humanities, School of Languages and Literatures, 2023
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- Date Issued: 2023-10-13
Towards interrogating the notion of a Black aesthetic in multi-cultural Africa
- Authors: Maina, Muhunyo
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/425231 , vital:72221
- Description: Enbargoed. Expected release date 2025. , Thesis (MA) -- Faculty of Humanities, Fine Art, 2023
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- Date Issued: 2023-10-13
Microbial and extracellular polymeric substance dynamics in arid–zone temporary pan ecosystems
- Authors: Bute, Tafara Frank
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422258 , vital:71925
- Description: Microbial communities of bacteria, viruses, algae, protozoans and fungi participate profoundly in aquatic systems, particularly in mediating processes such as primary production, decomposition, and biogeochemical cycles. In addition, microbiomes produce extracellular polymeric substances (EPS) which encompass a hydrated exopolymer mainly constituted of carbohydrates and proteins. The exopolymer aid proliferation and persistence of biofilms on their resident surfaces. There is however paucity of data on functional diversity of microbiomes in arid zone temporary wetlands with previous research having mainly focused on permanent systems in the northern hemisphere. In the face of ongoing climatic changes and anthropogenic threats to wetlands, it is imperative to assess the health status of aquatic systems in relation to microbial productivity dynamics. In this thesis, colorimetric methods and sequence–based metagenomics were conducted to quantify microbial EPS production and bacterial metagenome functions, respectively. This study was conducted in Khakhea–Bray region (North–West, South Africa) in June 2021 and January 2022 with a focus on evaluating microbial patterns of distribution between seasons (i.e., Dry and Wet) and varying depth i.e., deepest zones (Deep), intermediate depth (Mid) and shallowest regions (Edge). Additionally, potential relationships between EPS and either water content or organic matter content (OM content) were evaluated. In this study it was hypothesized that wet phases and deeper zones will have high EPS production and support more functions in comparison to shallowest regions and dry phases. Carbohydrates and proteins were quantified using the Dubois method and modified Lowry procedure, respectively. Carbohydrates generally occurred in higher proportions than proteins, suggesting that EPS found in these systems was largely diatom produced. The wet phases (wet season and inundation periods) supported more EPS production compared to the dry phases. The results of principal components analysis (PCA) and Spearman’s correlations suggested that EPS was highly correlated with sediment water content among other assessed variables. No significant associations were established between EPS and organic matter content. Spatial distribution of EPS demonstrated similar patterns between the deepest (Deep) and the intermediate depth zones (Mid) however the shallow regions (Edge) had significantly lower concentrations. Bacterial characterization was established by amplification of the 16S rRNA gene using illumina–sequencing protocol. Enzyme functions associated with biogeochemical pathways were predicted in PICRUSt2 bioinformatics pipeline. A total of 15 042 Unique Amplicon Sequence Variants (ASVs) were observed to be affiliated to 51 bacterial phyla and 1 127 genera. All top genera had commonality in heat tolerance. Firmicutes, dominated at phyla level with 59 % (mean ± sd, 19 ± 13 %) relative abundance followed by Actinobacteria and Proteobacteria both at 34 % (18 ± 7 %) and (18 ± 6 %), respectively. Microbial diversity matrices highlighted significant differences in beta diversity more than alpha diversity. Bacterial microbiomes were more distinct between seasons compared to within season, suggesting that functions were seasonally driven. These findings were supported by highest rates of denitrification, carbohydrate degradation and EPS production by core microbiomes in the wet season as compared to low rates of nitrogen mineralisation, carbon fixation and nitrification in the dry season. The present findings represent a first attempt in evaluating sequence–based metagenomics in semi–arid southern African temporary pan ecosystem. Both microbial EPS and bacterial functional potential were highly driven by water availability, with highest rates mainly associated with maximum inundation compared to dry states of pans. It can therefore be suggested that extended dry periods are threatening to microbially mediated processes in temporary wetlands, with implications to loss of biodiversity due to desiccation resulting in poor nutrient cycling. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
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- Date Issued: 2023-03-29
Photodynamic therapy using morpholine substituted porphyrins in the presence of cancer specific molecules linked to graphene quantum dots
- Authors: Magaela, Ngwanabjala Bridged
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422486 , vital:71947
- Description: This thesis reports on the synthesis, characterization, photophysiochemical properties of morpholine substituted symmetrical and asymmetrical porphyrins. The synthesized porphyrins are conjugated to cancer selective biomolecules (folic acid and biotin) which are linked to nitrogen doped graphene quantum dots, as potential photosensitizers for photodynamic therapy (PDT). The symmetrical morpholine porphyrin complexes 2 (Sn(IV) 5,10,15,20 tetra-4-morpholinyl porphyrin) and 3 (Zn 5,10,15,20 tetra-4-morpholinyl porphyrin) had the same substituent but different central metals, and they were both conjugated to biotin decorated nitrogen doped graphene quantum dots (B-NGQDs), however complex 2 (Sn(IV) 5,10,15,20 tetra-4-morpholinyl porphyrin) was conjugated to B-NGQDs through an ester bond and complex 3 (Zinc 5,10,15,20 tetra-4-morpholinyl porphyrin) through 𝜋-𝜋 stacking. The effect of asymmetry was studied by comparing complex 3 (Zn 5,10,15,20 tetra-4-morpholinyl porphyrin) and complex 5 (Zn 5- bromophenyl-10-15-20-(tris-4- morpholinyl) porphyrin). Complex 5 (Zn 5- bromophenyl-10-15-20-(tris-4- morpholinyl) porphyrin) was an asymmetric porphyrin with morpholine and bromine as substituents. It was observed that asymmetry enhances singlet oxygen quantum yield and PDT activity. It was also observed that folic acid is a better targeting biomolecule when compared to biotin, and this was studied by comparing complex 3 conjugated to B-NGQDs and complex 3 conjugated to folic acid decorated nitrogen doped graphene quantum dots (FA-NGQDs). 3-FA-NGQDs had a better cellular uptake and PDT activity. , Thesis (MSc) -- Faculty of Science, Chemistry, 2023
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- Date Issued: 2023-03-29
The development of a low-cost real- time bacterial plate culture monitoring system
- Authors: Songcata, Ntobeko
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422437 , vital:71942
- Description: Access restricted. Access embargoed until 2025. , Thesis (MSc) -- Faculty of Science, Biotechnology Innovation Centre, 2023
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- Date Issued: 2023-03-29
The nature of Visual Representations of multiplication and division exercises in nine Grades 1 to 3 South African textbooks
- Authors: Booysen, Tammy Irene
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422579 , vital:71959
- Description: Mathematics is a language that is rich in visual representations (Mudaly & Rampersad, 2010). Visual Representations assist us in developing our reasoning skills when solving a problem and our understanding of the relationships between concepts (Ozkan et al., 2018). This thesis focuses on the different visual representations (VR) in South African Foundation Phase mathematics textbooks and workbooks. Textbooks and workbooks play an important role in developing an understanding of mathematical concepts for both teachers and learners (Harries & Spooner, 2000). While teachers generally rely heavily on textbooks, they were a key resource while schools were closed due to COVID-19 lockdown regulations. The theory of Constructivism forms part of the theoretical framework for this study. Constructivism advocates that learners actively construct knowledge through experiences rather than passively receiving knowledge from the outside (Von Glaserfeld, 2001). Vygotsky believed that social interactions create experiences that facilitate the learning and meaning-making process (Vygotsky, 1978). This case study is underpinned by an interpretivist paradigm as it sought to examine the nature of VRs in three Grades 1 - 3 textbooks/workbooks. My research approach is primarily qualitative with descriptive statistics to assist in developing a more comprehensive understanding of the research questions. The study was guided by the analytic tool designed by Fotakopoulou and Spiliotopoulou (2008) which I adapted for Foundation Phase mathematics use. The framework provides insight on the type of VR, VRs relation to content, VRs relation to reality, the function of the VR and dimensionality of a VR. While the workbooks had many more VRs than textbooks, the dominant type of VR in textbooks and workbooks are images. The VRs mostly have a strong relation to content with a realistic relation to reality as they were predominantly 2D representation of a 3D object that had an exemplifying function (type b). , Thesis (MEd) -- Faculty of Education, Education, 2023
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- Date Issued: 2023-03-29