Browsing by Author "Roberts, Elise"

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    Investigations into the ecology and management of the polyphagous shot hole borer beetle (PSHB, Euwallacea fornicatus) in South Africa
    (Stellenbosch : Stellenbosch University, 2023-12) Roberts, Elise; Roets, Francois; Paap, Trudy; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The polyphagous shot hole borer beetle (PSHB) (Euwallacea fornicatus) (Coleoptera: Curculionidae: Scolytinae) and its primary fungal symbiont, Fusarium euwallaceae, is a pest-disease complex that has killed a wide range of tree species in multiple countries on six continents, including South Africa. As with any invasive pest, monitoring programmes reveal the drivers behind species population dynamics in invaded regions, which helps to mitigate potential impacts and inform management strategies. This study involved a 26- month monitoring programme in an urban-agricultural fringe setting of the Western Cape province, South Africa. Baited traps were used to determine activity patterns in comparison with temperature, as well as infestation dynamics over time in comparison with climatic and biological factors. Results suggest that activity is strongly temperature dependent, and numbers peak in late summer. The number of surrounding infested reproductive hosts was an important explanatory variable for increasing beetle abundance and infestation levels, while focal tree infestation “saturation”, tree stress and tree size may also play a role. Infested host tree removal may be important for agricultural areas where crops are surrounded by reproductive hosts either deliberately planted as windbreaks or growing naturally. Two prominent management strategies for invasive forest pests were trialled: tree removal and therapeutic chemical treatment. Results suggest that tree removal and appropriate disposal of infested wood can decrease local propagule pressure, especially if conducted in colder months. Furthermore, some therapeutic chemical treatments reduced fungal growth, number of new PSHB attacks, and beetle colony success, but control was never completely successful. These results indicate that a combination of physical and chemical control options may help to reduce propagule pressure, but is unlikely to prevent infestations for long periods.