Pre-release evaluation of stem-galling and seed-feeding midges (Diptera: Cecidomyiidae) from South Africa as biological control agents for Guinea grass (Megathyrsus maximus) in Texas, United States
- Authors: De la Fontaine, Benjamin
- Date: 2025-04-02
- Subjects: Guinea grass Biological control Texas , Gall midges , Invasive plants Biological control Texas , Maxent , Phylogeny , Grasses Texas
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479002 , vital:78248
- Description: Guinea grass (Megathyrsus maximus) is a tall-statured C4 grass with a native range spanning sub-Saharan Africa. Intentionally exported for centuries for its grazing value, it has become a near-global invasive. Texas, USA is the first territory to initiate a biological control program for Guinea grass, targeting an invasive population with genetic origins that have been traced to South Africa. This study focuses on the identification and evaluation of biological control agents for Guinea grass. Native-range natural enemy surveys were performed in South Africa, resulting in the identification of several undescribed species of phytophagous midges (Diptera: Cecidomyiidae) on Guinea grass, including stem-galling taxa (gall midges) and seed-feeding taxa (seed midges). These taxa are expected to be highly host-specific based on the known biology of this family of insects, but the difficulty of rearing them in the laboratory necessitated field-based assessments. Field host range assessments of stem gall midges resulted in the rejection of one candidate (the horn gall midge, undescribed sp.) due to feeding on a relative of the target plant, Batochloa deusta, and the prioritization of another candidate (the blister gall midge, Arabukodiplosis vesicaria) that feeds only on Megathyrsus maximus. Combined field host range evaluations and phylogenetic analysis of a cryptic species complex of seed midges resolved this as a new genus containing up to seven species, with five species that are likely to be specific to their respective Panicoideae grass hosts, including Megathyrsus maximus and Cenchrus ciliaris (buffelgrass – also invasive in the USA). Climate matching models for the blister gall midge and seed midge on Guinea grass predicted high likelihood of establishment and nearly complete coverage of invaded sites in Texas, and identified northern KwaZulu-Natal, South Africa as an ideal source region for Guinea grass biocontrol agents. The nascent sub-field of grass biocontrol research has developed slowly because of inaccurate perceptions that grasses lack host-specific herbivores, and faces a severe taxonomic impediment given the large number of undescribed insect species feeding on grasses, especially in Africa. This study has contributed to resolving both challenges by identifying several new host-specific insect species, showing that the prospects for future success and discovery in grass biological control are promising. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2025
- Full Text:
- Date Issued: 2025-04-02
- Authors: De la Fontaine, Benjamin
- Date: 2025-04-02
- Subjects: Guinea grass Biological control Texas , Gall midges , Invasive plants Biological control Texas , Maxent , Phylogeny , Grasses Texas
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/479002 , vital:78248
- Description: Guinea grass (Megathyrsus maximus) is a tall-statured C4 grass with a native range spanning sub-Saharan Africa. Intentionally exported for centuries for its grazing value, it has become a near-global invasive. Texas, USA is the first territory to initiate a biological control program for Guinea grass, targeting an invasive population with genetic origins that have been traced to South Africa. This study focuses on the identification and evaluation of biological control agents for Guinea grass. Native-range natural enemy surveys were performed in South Africa, resulting in the identification of several undescribed species of phytophagous midges (Diptera: Cecidomyiidae) on Guinea grass, including stem-galling taxa (gall midges) and seed-feeding taxa (seed midges). These taxa are expected to be highly host-specific based on the known biology of this family of insects, but the difficulty of rearing them in the laboratory necessitated field-based assessments. Field host range assessments of stem gall midges resulted in the rejection of one candidate (the horn gall midge, undescribed sp.) due to feeding on a relative of the target plant, Batochloa deusta, and the prioritization of another candidate (the blister gall midge, Arabukodiplosis vesicaria) that feeds only on Megathyrsus maximus. Combined field host range evaluations and phylogenetic analysis of a cryptic species complex of seed midges resolved this as a new genus containing up to seven species, with five species that are likely to be specific to their respective Panicoideae grass hosts, including Megathyrsus maximus and Cenchrus ciliaris (buffelgrass – also invasive in the USA). Climate matching models for the blister gall midge and seed midge on Guinea grass predicted high likelihood of establishment and nearly complete coverage of invaded sites in Texas, and identified northern KwaZulu-Natal, South Africa as an ideal source region for Guinea grass biocontrol agents. The nascent sub-field of grass biocontrol research has developed slowly because of inaccurate perceptions that grasses lack host-specific herbivores, and faces a severe taxonomic impediment given the large number of undescribed insect species feeding on grasses, especially in Africa. This study has contributed to resolving both challenges by identifying several new host-specific insect species, showing that the prospects for future success and discovery in grass biological control are promising. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2025
- Full Text:
- Date Issued: 2025-04-02
Phylogeography and comparative ecophysiology of Chrysanthemoides Turn. Ex Medik. (Tribe Calenduleae)
- Authors: Howis, Seranne
- Date: 2005
- Subjects: Chrysanthemoides , Phylogeny , Ecophysiology , DNA , Plant genetics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4256 , http://hdl.handle.net/10962/d1008189
- Description: Chrysanthem Oides is a common Southern African shrub that grows in a variety of habitats. From coastal shrubland and fynbos to mountainous areas as far north as Kenya. The genus has two species and 8 subspecies. The diagnoses and delimitation of which have been based almost exclusively on morphological characteristics. This project aims to investigate, with the use of phylogenetic species concepts. The validity of these subspecies. Unlike biological species concepts that rely on reproductive isolation as a defining character of a species. Phylogenetic species concepts (PSC) are concerned with delimiting evolutionary significant units (ESUs). ESUs are evolutionarily isolated lineages, and under the PSC a species is an aggregation of organisms consistently diagnosable by a fixed character or combination of characters. This project therefore searched for genetic and physiological characters by which to delimit ESUs within the Cill), samhemoides genus. DNA sequencing was used to investigate the genetic characters, while gas exchange studies were used to investigate the ecophysiological characters. DNA sequence analysis indicated that the ESUs can be diagnosed by genetic means and that one species may be of hybrid origin. Field studies of three disparate genetically identifiable ESUs from three disparate climates found that there are noticeable differences in ecophysiological responses of these ESUs in the field. Plants from each ESU were transferred to a greenhouse and grown under identical conditions for several months and compared to determine if these traits are inherent, or elastic in relation to environmental conditions. Under simulated high rainfall conditions. There does not appear to be a significant difference in the photosynthetic traits.
- Full Text:
- Date Issued: 2005
Phylogeography and comparative ecophysiology of Chrysanthemoides Turn. Ex Medik. (Tribe Calenduleae)
- Authors: Howis, Seranne
- Date: 2005
- Subjects: Chrysanthemoides , Phylogeny , Ecophysiology , DNA , Plant genetics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4256 , http://hdl.handle.net/10962/d1008189
- Description: Chrysanthem Oides is a common Southern African shrub that grows in a variety of habitats. From coastal shrubland and fynbos to mountainous areas as far north as Kenya. The genus has two species and 8 subspecies. The diagnoses and delimitation of which have been based almost exclusively on morphological characteristics. This project aims to investigate, with the use of phylogenetic species concepts. The validity of these subspecies. Unlike biological species concepts that rely on reproductive isolation as a defining character of a species. Phylogenetic species concepts (PSC) are concerned with delimiting evolutionary significant units (ESUs). ESUs are evolutionarily isolated lineages, and under the PSC a species is an aggregation of organisms consistently diagnosable by a fixed character or combination of characters. This project therefore searched for genetic and physiological characters by which to delimit ESUs within the Cill), samhemoides genus. DNA sequencing was used to investigate the genetic characters, while gas exchange studies were used to investigate the ecophysiological characters. DNA sequence analysis indicated that the ESUs can be diagnosed by genetic means and that one species may be of hybrid origin. Field studies of three disparate genetically identifiable ESUs from three disparate climates found that there are noticeable differences in ecophysiological responses of these ESUs in the field. Plants from each ESU were transferred to a greenhouse and grown under identical conditions for several months and compared to determine if these traits are inherent, or elastic in relation to environmental conditions. Under simulated high rainfall conditions. There does not appear to be a significant difference in the photosynthetic traits.
- Full Text:
- Date Issued: 2005
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