Using the larval parasitoid, Agathis bishopi (Nixon) (Hymenoptera: Braconidae), for early detection of false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) infested fruit
- Authors: Zimba, Kennedy Josaya
- Date: 2015
- Subjects: Cryptophlebia leucotreta , Citrus -- Diseases and pests -- South Africa , Pests -- Biological control -- South Africa , Cryptophlebia leucotreta -- Detection , Parasitoids -- Hosts , Braconidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5919 , http://hdl.handle.net/10962/d1017186
- Description: Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is one of the major citrus pests of economic importance for South Africa’s citrus industry. It is endemic to Africa, and therefore a phytosanitary pest with zero tolerance by most export markets. The cryptic nature of T. leucotreta makes visual inspection an inefficient method for detecting neonate larvae in fruit in the packhouse. Therefore, a more accurate method for sorting infested fruit at the packhouse, particularly for newly infested fruit could ensure market access. A recent study showed that fruit infested by T. leucotreta emit a chemical profile different from that of a healthy fruit. Several studies provide evidence that parasitoids locate their hosts feeding on fruit by exploiting the novel chemical profiles produced due to host herbivory. The aim of this study was to evaluate the potential of using the naturally occurring behaviour of a larval parasitoid Agathis bishopi (Nixon) (Hymenoptera: Braconidae) for detection of T. leucotreta infested fruit, by determining which compound in infested fruit is attractive to parasitoids. Ytube olfactometer and flight-tunnel bioassays with healthy and T. leucotreta infested fruit showed a significantly stronger response of A. bishopi female parasitoids to infested fruit. Among the volatile compounds associated with T. leucotreta infested fruit, D-limonene elicited the strongest attraction to A. bishopi female parasitoids. Attraction of mated A. bishopi female parasitoids to T. leucotreta infested fruit and D-limonene significantly increased after oviposition experience. Behavioural responses of A. bishopi female parasitoids that were associated with T. leucotreta infested fruit were investigated to determine which behaviours are distinct and interpretable. Probing and oviposition behaviours were the most noticeable and were only elicited on infested fruit when parasitoids contacted T. leucotreta frass, indicating that chemical compounds in frass are short-range cues used for final host location. Since production of D-limonene by fruit is elevated due to herbivory by different pests including mechanical injury on fruit, response of A. bishopi female parasitoids to compounds in frass offers a more specific and potentially useful mechanism for development of a detection system for T. leucotreta infested fruit. Chemical analysis of T. leucotreta frass and conditioning A. bishopi parasitoids to respond behaviourally to compounds in frass is proposed.
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- Date Issued: 2015
An analysis of "self-determination" in international law : the case of South Sudan
- Authors: Zimuto, Prince Charles
- Date: 2015
- Subjects: Self-determination, National Decolonization -- South Sudan Sudan -- Politics and government
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: http://hdl.handle.net/10353/5697 , vital:29364
- Description: This research intends to investigate the scope and applicability of the concept of ‘self-determination’ outside the context of decolonisation using South Sudan as a case study. Demands for the exercise of the right to self-determination are widespread. These are vehemently resisted by states who view the concept of ‘self-determination’ as a potential source of territorial disintegration. International instruments which provide for the right to self-determination also discourage the impairment of the territorial integrity of states in the name of self-determination. The problem faced in international law is therefore how to balance the right to self-determination with the principle of territorial integrity. The study reveals that the general understanding is that outside the context of decolonisation the right to self-determination may be exercised within the territorial boundaries of a state without compromising the territorial integrity of a state. The internal exercise of the right to self-determination entails human rights protection, participation in the political affairs of the state and autonomy arrangements. This general understanding is however problematic where a state systemically violates the rights of its people and denies them political participation in the affairs of the state. The people of South Sudan found themselves in such a situation from the time when Sudan gained independence from British colonial rule. Despite a number of negotiations with the government of Sudan, the people of South Sudan continued to be marginalised and their rights violated with impunity. They then demanded to exercise their right to self-determination externally and eventually they seceded from Sudan through the framework created by the Comprehensive Peace Agreement of 2005. In the light of the secession of South Sudan from Sudan this study proposes a remedial self-determination approach to the understanding of post-colonial self-determination. In terms of this approach when people are denied the right to exercise their right to self-determination internally, or their rights are deliberately and systemically violated, they may exercise their right to self-determination externally and secede.
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- Date Issued: 2015
Stalking black swans, dragon kings, and market crashes on the JSE
- Authors: Zuka, Mawethu
- Date: 2015
- Subjects: Johannesburg Stock Exchange -- Research Stock exchanges -- South Africa , Stocks -- South Africa -- Johannesburg Financial crises -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/18376 , vital:28631
- Description: This paper examines bubbles on the JSE All Share Index as well as the critical time of the stock market crash from 2/01/ 2004 – 27/03/2014. The underlying hypothesis define bubbles as extreme and begin as a group of small events which grow in a super exponential form explained by a log periodic power law model (LPPL model). The hypothesis is based on the assumption of investors’ herding behavior, where investors collude by making investment decision correlated with their counterparties. The paper implements a Savitzky Golary Algorithm to detect peaks and calculate the critical time of the crash from the peaks. An Ordinary Least Squares (OLS) method is used to determine both the value of stock market price index at the critical time and the increase in the stock market price index over the time before the crash. The remaining parameters of the LPPL model are estimated using a Maximum Likelihood Estimation method. On the empirical results; 68 peaks were detected, and the LPPL model at the critical crash time is estimated 34736.586. Five bubbles are detected; the 15/8/2005 bubble, 28/5/2013 bubble, 23/8/2013 bubble, 5/11/2013, and 1/20/2014.
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- Date Issued: 2015