- Title
- The effects of elevated CO2 on feeding guild responses of biological control agents of Pontederia crassipes Mart. (Pontederiaceae)
- Creator
- Paper, Matthew Keenan
- ThesisAdvisor
- Hill, M P
- ThesisAdvisor
- Coetzee, Julie
- Subject
- Carbon dioxide
- Subject
- Pontederia crassipes
- Subject
- Biological pest control agents
- Subject
- Invasive plants Biological control
- Subject
- Pontederiaceae Climatic factors
- Date
- 2022-04-06
- Type
- Academic theses
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10962/455338
- Identifier
- vital:75422
- Description
- Elevated CO2 (eCO2) and rising global temperatures have the potential to alter plant-insect interactions with important implications for plant community structure and function. Previous studies on plant-insect interactions have shown that eCO2 will affect insect feeding guilds differently, impacting negatively, positively or having very little effect. The implications of this on the global invasive plant biological control programme is largely unknown. This study investigates the response of one of the world’s most invasive aquatic plants, Pontederia ( = Eichhornia) crassipes Mart. (Pontederiaceae), to predicted eCO2 conditions of 800 ppm and how this may affect the feeding response of two biological control agents representing different feeding guilds; the leaf chewing Cornops aquaticum Brüner (Orthoptera: Acrididae) and the phloem-feeding Megamelus scutellaris Berg (Hemiptera: Delphacidae). A factorial eCO2 x feeding impact study was conducted at the Rhodes University Elevated CO2 Facility in the Eastern Cape Province of South Africa over 13 weeks in the growing season of 2019. The effect of insect herbivory by C. aquaticum and M. scutellaris at two atmospheric CO2 concentrations, representing current and future predicted concentrations (400 ppm and 800 ppm) on P. crassipes was examined through both biomass and ecophysiological measures. Assimilation rates, C:N ratio, total dry weight and relative growth rate of P. crassipes were unaffected by eCO2 conditions, and plants experienced no CO2 fertilization in eutrophic water conditions representative of South African waterways. Effects of eCO2 on insect herbivory varied depending on the feeding guild. Pontederia crassipes showed compensatory growth responses when exposed to C. aquaticum herbivory regardless of CO2 treatment, but chewing herbivory damage remained constant, and the agent maintained efficacy. Pontederia crassipes showed down-regulation of photosynthesis when exposed to M. scutellaris due to eCO2-related feeding responses by M. scutellaris increasing substantially through a significant (30%) increase in adult population density under eCO2 conditions. These results indicate that the plant-insect interactions that underpin biological control programmes for P. crassipes should remain successful under future CO2 conditions. Phloem-feeding insect damage (M. scutellaris) was significantly greater than chewing damage in this study, suggesting that invasive plant biological control programmes will need to shift focus away from the charismatic chewing insect herbivores and onto the often-neglected phloem-feeding biological control agents due to their overwhelmingly positive response to eCO2.
- Description
- Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Format
- computer, online resource, application/pdf, 1 online resource (98 pages), pdf
- Publisher
- Rhodes University, Faculty of Science, Zoology and Entomology
- Language
- English
- Rights
- Paper, Matthew Keenan
- 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 | SOURCE1 | PAPER-MSC-TR22-289.pdf | 1 MB | Adobe Acrobat PDF | View Details |