Prioritising biological control agents for release against Sporobolus pyramidalis and Sporobolus natalensis (Poaceae) in Australia
- Authors: Sutton, Guy Frederick
- Date: 2021
- Subjects: Grasses -- Diseases and pests , Bruchophagus , Wasps , Alien plants -- Biological control -- Australia , Sporobolus -- Biological control -- Africa , Sporobolus -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insects as biological pest control agents -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/172445 , vital:42201 , 10.21504/10962/172445
- Description: Sporobolus pyramidalis Beauv. and S. natalensis (Steud.) Th. Dur. and Schinz. (giant rat’s tail grass) (Poaceae), invade rangelands and pastures in eastern Australia, costing the livestock industry approximately AUS$ 60 million per annum in grazing losses. Mechanical and chemical control options are costly and largely ineffective. Biological control is viewed as the most promising control option, however this management strategy has largely been avoided for grasses, due to their perceived lack of suitably host-specific and damaging natural enemies. In this thesis, the prospects for using biological control against S. pyramidalis and S. natalensis in Australia was assessed, in light of these potential challenges. Climate matching models were used to identify high-priority geographic regions within the plants’ native distributions to survey for potential biological control agents. High-priority regions to perform surveys were identified by modelling the climatic suitability for S. pyramidalis and S. natalensis in sub-Saharan Africa (i.e. their potential native ranges’), and climatic compatibility with regions where biological control is intended in Australia. High-priority regions for S. pyramidalis included: (1) coastal East Africa, ranging from north-eastern South Africa to Uganda, including south-eastern DRC, (2) some parts of West Africa, including inland regions of the Ivory Coast and western Nigeria, (3) northern Angola and (4) eastern Madagascar, and for S. natalensis included: (1) eastern South Africa, (2) eastern Zimbabwe, (3) Burundi, (4) central Ethiopia and (5) central Madagascar. Prospective control agents collected from these regions have the highest probability of establishing and proliferating in Australia, if released. In surveys of the insect assemblages on S. pyramidalis and S. natalensis in the climatically-matched region of eastern South Africa fifteen insect herbivores associated with the grasses were identified. Insect feeding guild, geographic distributions, and seasonal abundances suggest that three stem-boring phytophagous wasps, Tetramesa sp. 1, Tetramesa sp. 2 and Bruchophagus sp. 1 (Hymenoptera: Eurytomidae), have potential as control agents. Species accumulation curves indicated that additional surveys in South Africa are unlikely to yield additional potential control agents. Field host-range surveys of 47 non-target grass species in South Africa showed that Tetramesa sp. 1, Tetramesa sp. 2, and Bruchophagus sp. 1, were only recorded from S. pyramidalis and S. natalensis. Integrating field host-range with phylogenetic relationships between plant species indicated that no native Australian Sporobolus species or economic crops and pastures are expected to be attacked by these wasps. All three wasp species are predicted to be suitably host-specific for release in Australia. Three other endophagous herbivores attacked non-target native African Sporobolus species that share a close phylogenetic relationship to native Australian Sporobolus species, and therefore, demonstrate considerable risk of non-target damage. These species should not be considered as potential control agents. Under native-range, open-field conditions, Tetramesa sp. 1 caused an approximately 5-fold greater reduction in plant survival and reproductive output than Tetramesa sp. 2 and Bruchophagus sp. 1. Tetramesa sp. 1 in combination with Tetramesa sp. 2 did not significantly increase the level of damage, while Bruchophagus sp. 1 may decrease the efficiency of Tetramesa sp. 1, if released in combination. Tetramesa 1 is therefore the most promising candidate agent. Prioritising potential agents using predicted efficacy allowed otherwise equally suitable prospective agents to be prioritised in a strategic manner. Prioritising which natural enemies to target as biological control agents is a complex task. Field host range and damage assessments in the native range may provide more realistic data than typical studies performed under artificial conditions in a laboratory or quarantine. Moreover, it could assist practitioners in prioritising the most suitable agent(s) at the earliest stage in the programme as possible. This study demonstrated that grasses are suitable targets for biological control as they can harbour host-specific and damaging natural enemies.
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- Date Issued: 2021
Investigations into biological control options for Lycium ferocissimum Miers, African Boxthorn (Solanaceae) for Australia
- Authors: Mauda, Evans Vusani
- Date: 2020
- Subjects: Lycium ferocissimum , Solanaceae -- Biological control -- Australia , Weeds -- Control -- Australia , Invasive plants -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insect-plant relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167142 , vital:41441
- Description: Lycium ferocissimum Miers (Solanaceae) (African boxthorn or boxthorn) is a shrub native to South Africa,and has become naturalised and invasive in Australia and New Zealand. The plant is listed on the Noxious Weed List for Australian States and territories. Although other control methods are available, biological control presents a potentially sustainable intervention for reducing populations of this weed in Australia. In South Africa, the plant has been recorded from two allopatric populations, one in the Eastern Cape Province, the other in the Western Cape Provinces, however, there taxonomic and morphological uncertainties are reported in the literature. Therefore, before native range surveys for potential biological control agents could be considered, the taxonomic uncertainty needed to be resolved. The two geographically distinct areas, as well as the Australia population were sampled to assess morphological and genetic variation. All samples collected in Australia were confirmed as L.ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L.ferocissimum across South Africa was high, and Australia was low, with no evidence of genetic seperation. One ehaplotypes found across Australia was found at only two sites in South Africa, both in the Western Cape, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa, putatively identified in the field as L.ferocissimum, were genetically characterised as different (unidentified) Lycium species. The majority of plants sampled were confirmed as L.ferocissimum, sharing a common haplotype (haplotype 5) with sampled specimens from Australia. Morphological analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L.ferocissimum, and thus morphological identification in the native range remains problematic. Surveys for phytophagous in sects on L.ferocissimum were carried out regularly over a two-year period in the two regions. The number of insect species found in the Eastern Cape Province (55) was higher than in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles, Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae), and the leaf-mining weevil, Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Native range studies such as this are perhaps the most technically difficult and logistically time-consuming part of the biological control programme. Yet, the entire outcome of a programme depends on the suite of potential agents feeding on the weed. The information gained during this stage significantly contributed to the prioritization of agents for further host-range testing and possible release. Here we showed how molecular and genetic characterisations of the target weed can be us ed to accurately define the identity and phylogeny of the target species. In addition, the study also highlighted the importance of considering plant morphology and how phenotypic plasticity may influence infield plant identifications while conducting native range surveys. By gaining further information during long-term and wide spread native range surveys we were not just able to provide a list of herbivorous insect fauna and fungi associated with the plant, but were able to prioritise the phytophagous species that held the most potential as biological control agents.
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- Date Issued: 2020