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Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa
Acacia cyclops A. Cunn. ex G. Don is an invasive alien plant that invades fynbos and coastal dunes. Several acacia species are grown commercially in South Africa and this has limited biocontrol agents to those that reduce only reproductive capacity. Dasineura dielsii was released in 2002 as a biocon...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| _version_ | 1867613311189647361 |
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| access_status_str | Open Access |
| author | Wheat, Nicola M |
| author2 | Richardson, David Mark |
| author_browse | Richardson, David Mark Wheat, Nicola M |
| author_facet | Richardson, David Mark Wheat, Nicola M |
| author_sort | Wheat, Nicola M |
| collection | Thesis |
| description | Acacia cyclops A. Cunn. ex G. Don is an invasive alien plant that invades fynbos and coastal dunes. Several acacia species are grown commercially in South Africa and this has limited biocontrol agents to those that reduce only reproductive capacity. Dasineura dielsii was released in 2002 as a biocontrol agent for A. cyclops. This gall-forming midge destroys inflorescences and prevents seedpods from forming, but allows continued harvesting. Insects overwinter as larvae within their galls. This study examined the levels of parasitism experienced by dormant D. dielsii larvae, as well as the trigger that causes them to break dormancy. Gall clusters were sampled over autumn and early winter, and were dissected to determine occupancy. The effects of temperature and light on dormant larvae were also examined. Observations showed that as the season progressed, more D. dielsii larvae entered dormancy. At the same time, a greater proportion of dormant larvae were parasitized. Parasitism was highest, at 18.5%, at the end of the study period, but this level of parasitism is not enough to reduce the biocontrol power of D. dielsii. A positive relationship between mass of gall clusters and the number of galls they contain was established. Larval dormancy could not be artificially broken by either light or temperature, and it appears that neither factor alone can trigger a break in dormancy. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/25722 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:06.076Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/25722 Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa Wheat, Nicola M Richardson, David Mark Hoffmann, John H Botany Plant Conservation Acacia cyclops A. Cunn. ex G. Don is an invasive alien plant that invades fynbos and coastal dunes. Several acacia species are grown commercially in South Africa and this has limited biocontrol agents to those that reduce only reproductive capacity. Dasineura dielsii was released in 2002 as a biocontrol agent for A. cyclops. This gall-forming midge destroys inflorescences and prevents seedpods from forming, but allows continued harvesting. Insects overwinter as larvae within their galls. This study examined the levels of parasitism experienced by dormant D. dielsii larvae, as well as the trigger that causes them to break dormancy. Gall clusters were sampled over autumn and early winter, and were dissected to determine occupancy. The effects of temperature and light on dormant larvae were also examined. Observations showed that as the season progressed, more D. dielsii larvae entered dormancy. At the same time, a greater proportion of dormant larvae were parasitized. Parasitism was highest, at 18.5%, at the end of the study period, but this level of parasitism is not enough to reduce the biocontrol power of D. dielsii. A positive relationship between mass of gall clusters and the number of galls they contain was established. Larval dormancy could not be artificially broken by either light or temperature, and it appears that neither factor alone can trigger a break in dormancy. 2017-10-23T06:30:13Z 2017-10-23T06:30:13Z 2004 2017-02-22T12:52:46Z Bachelor Thesis Honours BSc (Hons) http://hdl.handle.net/11427/25722 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Botany Plant Conservation Wheat, Nicola M Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| thesis_degree_str | Bachelor's / Honours |
| title | Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| title_full | Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| title_fullStr | Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| title_full_unstemmed | Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| title_short | Patterns of parasitism and emergence in the gall midge Dasineura Dielsii (Diptera: Cecidomyiidae) : a biological control agent of Acacia cyclops in South Africa |
| title_sort | patterns of parasitism and emergence in the gall midge dasineura dielsii diptera cecidomyiidae a biological control agent of acacia cyclops in south africa |
| topic | Botany Plant Conservation |
| url | http://hdl.handle.net/11427/25722 |
| work_keys_str_mv | AT wheatnicolam patternsofparasitismandemergenceinthegallmidgedasineuradielsiidipteracecidomyiidaeabiologicalcontrolagentofacaciacyclopsinsouthafrica |