A genetic analysis of the species and intraspecific lineages of Dactylopius Costa (Hemiptera: Dactylopiidae)
- Authors: Van Steenderen, Clarke Julian Mignon
- Date: 2020
- Subjects: Dactylopius
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/151491 , vital:39135
- Description: The Cactaceae family comprises 15 genera and nearly 2000 species. With one exception, these are all native to the Americas. Numerous cactaceous species are invasive in other parts of the world, resulting in considerable damage to ecosystem functioning and agricultural practices. The most successful biological control agents used to combat invasive Cactaceae belong to the Dactylopius genus (Hemiptera: Dactylopiidae), comprising eleven species. The Dactylopiidae are exclusively cactophagous and are usually host-specific. Some intraspecific lineages of dactylopiids, often referred to as `biotypes', also display host-specificity, and are used to control particular species of invasive Cactaceae. To date, two lineages within Dactylopius opuntiae (`ficus' and `stricta'), and two within D. tomentosus (`cholla' and `imbricata') have been released in South Africa to control Opuntia ficus-indica and O. stricta, and Cylindropuntia fulgida and C. imbricata, respectively. The `californica var. parkeri' lineage is currently under consideration for release in South Africa for the control of C. pallida. Australia has already released these five lineages, and approved the release of an additional three in 2017; namely D. tomentosus `bigelovii', `cylindropuntia sp.', and `acanthocarpa x echinocarpa'. Many of the Dactylopius species are so morphologically similar, and in the case of lineages, identical, that numerous misidentifications have been made in the past. These errors have had serious implications, such as failed attempts at the biological control of cactus weeds. This thesis aimed to generate a multi-locus genetic database to enable the identification of the species and lineages in the Dactylopiidae family, and to test its accuracy. Seven species were included in the analysis, including two lineages within D. opuntiae and six within D. tomentosus. Genetic characterisation was achieved through the DNA sequencing of three gene regions; namely mitochondrial 12S rRNA and cytochrome c oxidase I (COI), nuclear 18S rRNA, and fragment analysis using two inter-simple sequence repeats (ISSRs). Nucleotide sequences were very effective for species-level identification, where the 12S, 18S, and COI regions showed 100%, 94.59%, and 100% identification accuracy rates, respectively. Additionally, the 12S and COI markers distinguished between half of the D. tomentosus lineages (`californica', `cholla', and `imbricata'), with identification accuracies of 100%. The `echinocarpa x acanthocarpa', `bigelovii', and `cylindropuntia sp.' lineages formed one clade. None of the DNA genetic markers showed a separation between the `ficus' and `stricta' lineages within D. opuntiae. Fragment analysis through the use of ISSRs provided higher-resolution results, and addressed this gap by showing a well-supported separation between the two lineages, and between wild populations collected in the Eastern Cape Province in South Africa. The identification accuracy of the `ficus' and `stricta' lineages was 81.82%. This is the first time that a method has been developed that can distinguish between these lineages. An additional component of this thesis was the creation of three user-friendly R-based programs to assist with: 1. ISSR data processing. 2. The identification of query Dactylopius nucleotide sequences relative to the gene databases created here. 3. A graphical user interface (GUI) version of the R package `SPIDER', which is useful for the assessment of the accuracy of genetic barcode data. A successful biological control programme relies on the correct identification of the agent in question, and so it is imperative that cactus biological control practitioners are able to distinguish between Dactylopius species and lineages in order to release the most effective ones onto target Cactaceae. The laboratory protocols reported, and data processing tools created here, have largely addressed this need and offer valuable practical applications. These include: 1. The flagging of potential new species, cryptic species, and lineages of dactylopiid species released as new biocontrol agents. 2. Validating the identifications made by taxonomists based on morphology. 3. Confirming to which species, and, where applicable, to which lineage, a field-collected sample belongs. 4. Identifying hybrids resulting from lineage crosses. Ensuring that the correct Dactylopius species are utilised for biological control will improve the control of invasive Cactaceae and protect biodiversity and agricultural productivity.
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- Date Issued: 2020
Securing software development using developer access control
- Authors: Ongers, Grant
- Date: 2020
- Subjects: Computer software -- Development , Computers -- Access control , Computer security -- Software , Computer networks -- Security measures , Source code (Computer science) , Plug-ins (Computer programs) , Data encryption (Computer science) , Network Access Control , Data Loss Prevention , Google’s BeyondCorp , Confidentiality, Integrity and Availability (CIA) triad
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/149022 , vital:38796
- Description: This research is aimed at software development companies and highlights the unique information security concerns in the context of a non-malicious software developer’s work environment; and furthermore explores an application driven solution which focuses specifically on providing developer environments with access control for source code repositories. In order to achieve that, five goals were defined as discussed in section 1.3. The application designed to provide the developer environment with access control to source code repositories was modelled on lessons taken from the principles of Network Access Control (NAC), Data Loss Prevention (DLP), and Google’s BeyondCorp (GBC) for zero-trust end-user computing. The intention of this research is to provide software developers with maximum access to source code without compromising Confidentiality, as per the Confidentiality, Integrity and Availability (CIA) triad. Employing data gleaned from examining the characteristics of DLP, NAC, and Beyond- Corp—proof-of-concept code was developed to regulate access to the developer’s environment and source code. The system required sufficient flexibility to support the diversity of software development environments. In order to achieve this, a modular design was selected. The system comprised a client side agent and a plug-in-ready server component. The client side agent mounts and dismounts encrypted volumes containing source code. Furthermore, it provides the server with information of the client that is demanded by plug-ins. The server side service provided encryption keys to facilitate the mounting of the volumes and, through plug-ins, asked questions of the client agent to determine whether access should be granted. The solution was then tested with integration and system testing. There were plans to have it used by development teams who were then to be surveyed as to their view on the proof of concept but this proved impossible. The conclusion provides a basis by which organisations that develop software can better balance the two corners of the CIA triad most often in conflict: Confidentiality in terms of their source code against the Availability of the same to developers.
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- Date Issued: 2020
The design of a Shmashana for the Hindu community in the Baakens valley, Port Elizabeth
- Authors: Bolton, Daniel
- Date: 2017
- Subjects: Hindu temples -- South Africa -- Port Elizabeth -- Designs and plans , Hinduism -- South Africa -- Port Elizabeth City planning -- South Africa -- Port Elizabeth
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/17855 , vital:28461
- Description: This treatise explores the consolidation of the Hindu Community’s identity through the design of a Shmashana (Hindu cremation ground) which allows for the conservation and practice of one of their most important rituals, traditional funeral rites. The Hindu community was amongst the first settlers in Port Elizabeth and entrenched in the historical, culturally rich and diverse suburb of South End. South End was later destroyed by the apartheid government and the Hindu community, as well as other communities were forcefully removed from their homes in South End and relocated to other areas forming pockets of ghettos and a segregated city. The proposal to establish a Shmashana will enhance the Hindu community’s cultural identity and reconnect them to South End, as well as a step towards reconciliation for the injustices of apartheid. This study utilises a qualitative research framework using precedent studies and inductive reasoning to formulate a design approach to the Hindu culture and South End as a place and memory. This investigation reveals that for the creation of a Shmashana there are specific site criteria required combined with particular spatial and physical qualities in the location and the cultural and spiritual needs of the Hindu community. These aspects are examined through a phenomenological lens to create an environment which is meaningful to the community and the memory of the pre-apartheid South End district. The writings of Relph (1976), Shamai (2005), Norberg-Schulz (1985), Manzo (2003), Najafi and Shariff (2011) are used to understand a sense of place and how the architecture and users can relate to it. Peter Zumthor’s (2006) characteristics of an atmospheric environment are applied to create an experiential space while the writings of Thomas Barrie (1996) examine the experience of religious sacred space.
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- Date Issued: 2017
Sylvia Plath images of life in a poet of death
- Authors: Mather, Mary Lynn
- Date: 1992
- Subjects: Plath, Sylvia , Plath, Sylvia -- Criticism and interpretation
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2245 , http://hdl.handle.net/10962/d1002288 , Plath, Sylvia , Plath, Sylvia -- Criticism and interpretation
- Description: On a creative and a personal level, Sylvia Plath seems to have been fascinated by the relationship between life and death. Her work reflects an ongoing preoccupation with duality and a sense of tension between two opposing forces suffuses virtually every poem she wrote in the period from 1956 to early 1963. Because her attitude to both life and death is deeply ambivalent, Plath's poetry rests on a strong awareness of conflict and her art is characterized by a continual pull between extremes. This thesis is an examination of how she uses images of life in poems that ostensibly deal with death.While Plath draws on the events of her own life for her poetic material, she also converts her personal experiences into a universal myth. She was familiar with Robert Graves's eclectic study of the pagan nature deity, The White Goddess, and she seems to have incorporated part of his symbolism into her own code of images. In particular, she adopts Graves's triple goddess of nature as one of the dominant figures in her created world, for the White Goddess is associated with life and death alike.Plath's dichotomy of life and death works on different planes. Firstly, she frequently envisages the self as divided and the opposition between life and death takes on the dimensions of an internal psychological war. Secondly, she extends the battle between life and death to the creative sphere. Thirdly, she explores the idea of life as a journey from birth to death. The White Goddess is linked with the three natural realms of earth, sky and underworld. And Plath relies largely on seasonal, lunar and chthonic images in her poetry. Furthermore, the three colours of the goddess - white , red and black - are the dominant hues of her poetry.
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- Date Issued: 1992