Electronic Theses and Dissertations (Masters)

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Browsing Electronic Theses and Dissertations (Masters) by Author "Byrne, Marcus"

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    The influence of plant phenolic compounds on the host range of Coniatus tamarisci Fabr. (Coleoptera: Curculionidae): a potential biological control agent of invasive Tamarix L. (Caryophyllales: Tamaricaceae) Taxa in South Africa
    (University of the Witwatersrand, Johannesburg, 2022) Hatile, Sivenathi Luvolwethu; Byrne, Marcus; Mayonde, Samalesu
    Tamarix L. (Caryophyllales: Tamaricaceae) are halophyte species that are native to Eurasia, North Africa, and southwestern Africa. These phreatophyte trees or shrubs have become prominent and widespread invaders in North America, South America, Australia, and South Africa. In South Africa, the Alien and Invasive Species regulations of the National Environmental Management: Biodiversity Act 2014 (NEM:BA) has classified invasive Tamarix as category 1b invader, which require control. Thus, three potential biological control agents have undergone laboratory-based host-specificity trials for the long-term sustainable control of Tamarix. The first two of these biocontrol agents, Diorhabda carinulata (Desbrochers.) (Coleoptera: Chrysomelidae) and Trabutina mannipara (Hemprich & Ehrenberg) (Hemiptera: Pseudococcidae), both failed the laboratory-based host-specificity trials because they completed their life cycle on the indigenous T. usneoides E. Mey ex Bunge. Previously, potential biocontrol agents were selected based on their native distribution and the phylogenetic relatedness of the invasive weed to indigenous nontarget species. However, it has recently been suggested that secondary metabolites also play a major role in insect host selection, and thus should be considered to improve the selection criteria of potential biocontrol agents. The current study is based on the third biocontrol agent that recently underwent laboratory based host-specificity trials in South Africa, Coniatus tamarisci (Fabr.) (Coleoptera: Curculionidae). This was in conjunction with an analysis of the potential influence Tamarix phenolic compounds have on insect host selection. The results show that although C. tamarisci could complete its’ life cycle on T. usneoides, the weevil had a low affiliation/risk associated with the indigenous Tamarix taxon. This advocates for the conduction of open field host-specificity trials, which will allow for a better understanding of C. tamarisci behaviour in a natural setting. Regarding phenolic compounds, three phenolic acids have been identified as being significantly prominent in T. usneoides compared to the invasive Tamarix taxa present in South Africa. These are gallic acid, dehydrodigallic acid, and syringic acid. These compounds are associated with protection from plant herbivory, which could explain the behaviour of C. tamarisci when exposed to and reared on T. usneoides.