- Title
- Biological control of torch cactus in South Africa: finding a suitable agent for a non-native weed with an unknown indigenous distribution
- Creator
- Griffith, Tamzin Camilla
- Subject
- Uncatalogued
- Date Issued
- 2024-10-11
- Date
- 2024-10-11
- Type
- Academic theses
- Type
- Doctoral theses
- Type
- text
- Identifier
- http://hdl.handle.net/10962/466781
- Identifier
- vital:76778
- Identifier
- DOI https://doi.org/10.21504/10962/466781
- Description
- Trichocereus spachianus is an invasive cactus species in South Africa and poses challenges as a target for biological control due to confusion around its taxonomy and origin. Adapted to arid environments, this cactus is of particular concern in dry savannah and Karoo biomes, where its invasion of rangelands reduces grazing capacity for both indigenous wildlife and livestock. While previous records indicate that T. spachianus is indigenous to Argentina, recent field surveys have failed to verify its presence. Determining the origin of the target weed was important in developing a biological control programme since it enables the collection of potential agents directly from native populations of the target plant. Successful biological control programmes against cactus species in South Africa have often involved utilising both new associations and oligophagous insects, made possible because of the lack of indigenous and valued cacti in the region. Lack of T. spachianus locations in the native distribution, meant direct collection of insects from the target weed was not possible. Efforts to find biological control agents were focused on new associations between closely related cacti and their oligophagous herbivores. Suitability of multiple Hypogeococcus (mealybug) entities and a cochineal species, Dactylopius confertus, were investigated for their efficacy on various South African weedy cactus species, including T. spachianus. Findings revealed that none of the Hypogeococcus entities (species or lineages) were effective biological control agents, but D. confertus demonstrated potential as a biological control agent with a relatively high fecundity and survival rate on T. spachianus. Efficacy trials indicated that D. confertus could reach population densities sufficient to cause mortality of T. spachianus plants. Limited host specificity trials revealed that D. confertus was suitably host specific for release in South Africa, provided host specificity testing was conducted on additional plants. Approval and release of D. confertus has the potential to reduce the invasiveness of this damaging cactus in a sustainable and environmentally friendly manner.
- Description
- Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (148 pages)
- Format
- Publisher
- Rhodes University
- Publisher
- Faculty of Science, Zoology and Entomology
- Language
- English
- Rights
- Griffith, Tamzin Camilla
- Rights
- Use of this resource is governed by the terms and conditions of the Creative Commons "Attribution-NonCommercial-ShareAlike" License (http://creativecommons.org/licenses/by-nc-sa/2.0/)
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | GRIFFITH-PHD-TR24-289.pdf | 1 MB | Adobe Acrobat PDF | View Details Download |