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1
Baker, Jeanine. "Factors affecting the establishment of a classical biological control agent, the horehound plume moth (Wheeleria spilodactylus) in South Australia." Title page, summary and contents only, 2002. http://web4.library.adelaide.edu.au/theses/09PH/09phb1677.pdf.
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Includes bibliographical references (leaves 168-198) The horehound plume moth (Wheeleria spilodactylus Curits), an agent introduced to control the invasive weed horehound (Murrubium vulgare L.), was used as a model system to investigate factors believed to influence the successful establishment of an introduced natural enemy. Retrospectively tests the use of generic population viability analysis and decision making tools for determining optimal release strategies for the horehound plume moth in South Australia and to compare outcomes with the emprical data collected during the course of this project
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Minkey, David Mark. "Weed seed predation by ants in the crop growing areas of Western Australia." University of Western Australia. Faculty of Natural and Agricultural Sciences, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0089.
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[Truncated abstract] In the crop growing areas of Western Australia, two economically important weed species, Lolium rigidum Gaud. (annual ryegrass) and Raphanus raphanistrum L. (wild radish), have evolved widespread herbicide resistance to multiple chemistry groups. Consequently, grain growers in the region have adopted an integrated approach to weed management that includes many non herbicide tools, however many more are needed as these weed species become increasingly more difficult to control. This thesis examines, in a series of field trials carried out in the Western Australian crop growing area, the potential for weed seed predation of annual ryegrass and wild radish by naturally occurring granivores as a new weed management tool for grain growers . . . The study discusses the implications of these results with the view to manipulating predation of weed seed through agricultural management practices. Ants were shown to be the dominant seed predator in this environment, especially in the centre of fields. The study has identified that the ant species Melophorus turneri (Forel), Monomorium rothsteini (Forel), Pheidole hartmeyeri (Forel) and Rhytidoponera metallica (Smith) are potential biological control agents for annual ryegrass seeds while P. hartmeyeri was identified as the only species suitable for biological control of wild radish seed pods. Ants were found to be sensitive to disturbance and some to crop residue type and these effects are discussed in relation to seed removal. This study of weed seed predation in agricultural fields is the most complete in this environment and can be used to inform further work in this area. It has identified that naturally occurring granivores can be used as a weed management tool.
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Mayo, Gwenda Mary. "Genetic variation in Hypericum perforatum L. and resistance to the biological control agent Aculus hyperici liro /." Title page, table of contents and abstract only, 2004. http://web4.library.adelaide.edu.au/theses/09PH/09phm4731.pdf.
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Heystek, Fritz. "Laboratory and field host utilization by established biological control agents of Lantana camara L. in South Africa." Thesis, Rhodes University, 2006. http://eprints.ru.ac.za/255/.
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Gordon, Antony John. "The biological control of Hakea sericea Schrader by the Hakea seed-moth, Carposina autologa Meyrick, in South Africa." Thesis, Rhodes University, 1993. http://hdl.handle.net/10962/d1005330.
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Hakea sericea Schrader was introduced to South Africa from Australia and has become a major problem in nearly all the coastal mountain ranges of the Cape Province. The hakea seed-moth, Carposina autologa Meyrick was released in South Africa for the biological control of H. sericea. The impact of the moth on the canopy-stored seeds of H. sericea was evaluated at two study sites in the south-western Cape over three years. The moth has reduced the accumulated seeds at the two study sites by 59.4% and 42.6%, respectively. The moth has shown a surprising ability to disperse and establish new colonies at low population levels. Factors contributing to the slow colonization of C. autologa in South Africa was investigated. The moths appear to be unable to distinguish between healthy and previously attacked fruits; 42.5% of the eggs were laid on attacked fruits. Only 13.1% of the healthy fruits with eggs yielded mature larvae. The high pre-penetration mortality found in the present study is similar to that found in Australia. The effect of the indigenous fungus, Colletotrichum gloeosporioides (Penz.) Sacc., on both H. sericea and C. autologa was investigated. H. sericea trees and branches that die as a result of fungus cause the accumulated fruits on the affected trees or branches to dehisce. This seed loss occurs at a crucial stage during C. autologa larval development. Only 42.1% and 33.0% of the trees were found to be healthy at the two study sites, respectively. One seed crop will always be available for regeneration, since recruitment is linked to fires, and wild-fires occur at a stage when the latest seed crop has escaped attack by c. autologa. C. autologa was released at six sites in the south-western Cape by attaching egg-bearing follicles to healthy fruits in the field. Three release sites were evaluated the year following release to determine whether the moth established or not. The role of C. autologa in the H. sericea biological control programme is discussed. Although seed destruction by C. autologa is not severe, it is expected to contribute to the control of H. sericea.
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Alfaro, Lemus Ana Lilia. "Factors influencing the control of citrophilous mealybug Pseudococcus calceolarie (Maskell) by Coccophagus gurneyi Compere in the Riverland of South Australia." Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09IM/09iml562.pdf.
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Includes bibliographical references (leaves 102-114) The highly successful biological control of the citrophilous mealybug Pseudococcus calceolarie (Maskell) (CM) by the parasitic wasp Coccophagus gurneyi Compere in several countries led to the release of this parasitoid in the Riverland of South Australia as part of an integrated pest management program. However CM has not been successfully controlled in this region. The results of this study may help to explain the lack of effective biological control of CM in Riverland citrus.
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Stafford, Martha Louise. "Biological control as an integrated control method in the management of aquatic weeds in an urban environmental and socio-political landscape : case study : Cape Town Metropolitan Area." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013015.
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Aquatic weeds transform and degrade the ecosystems which they invade, impacting various aspects of their surroundings ranging from the community level to disrupting important processes affecting ecosystem services. All of the major aquatic weeds of South Africa are found in the Cape Town Metropolitan Area. Landowners, whether private or public, are legally obliged to manage the listed invasive species through applying environmentally acceptable methodologies. This thesis provides an overview of the strategic management options, prevention, early detection, rapid response and eradication of new invasions, and containment and control species of established species. It discusses the different control methods available for managing aquatic weeds, namely mechanical, manual, chemical and biological, and the integration of different methods to improve their effectiveness. Although various studies have shown that biological control is the most cost–effective, environmentally-friendly and sustainable method, it is not yet fully integrated into weed management programmes in South Africa. In addition, the successes achieved in other parts of the world with the control of water hyacinth through biological control have not been repeated in the urban environment, despite the fact that South Africa has the highest number of biological control agents available for the weed. Urbanisation puts pressure on the natural environment and ecosystem functioning. Nutrient-enriched waters support aquatic weed growth and pose a challenge to the management thereof, in particular with regard to integrating biological control into management programmes. The aims of this study were to determine the reasons for the lack of integration of biological control into weed management programmes in South Africa, to determine the feasibility of integrating biological control in aquatic weed management programmes in a complex urban environmental and socio-political landscape by means of three case studies in the Cape Town Metropolitan Area, which showed that biological control is feasible in urban environments and should be considered. Two surveys were conducted to determine the reasons for the lack of integration of biological control into weed management programmes. The surveys showed that there is a gap between research and implementation as a result of poor communication, non-supporting institutional arrangements and a lack of appropriate capacity and skills at the implementation level. Recommendations were offered to address these issues.
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Soleyman-Nezhadiyan, Ebrahim. "The ecology of Melangyna viridiceps and Simosyrphus grandicornis (Diptera : Syrphidae) and their impact on populations of the rose aphid, Macrosiphum rosae." Title page, contents and summary only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phs685.pdf.
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Bibliography: leaves 213-233. This thesis studies the influence of the two common syrphid species on populations of rose aphids in rose gardens in Adelaide. The study determines whether the provision of attractive flowers increases the suppressive effect of syrphids on rose aphids and analyses some ecological and biological aspects of two syrphid species -- Melangyana viridiceps (Macquart) and Simosyrphus grandicornis (Macquart) -- in a Mediteranean climate to obtain a better understanding of their biological control potential.
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Van, der Westhuizen Liamé. "The evaluation of Phenrica sp.2 (Coleoptera: Chrysomelidae: Alticinae), as a possible biological control agent for Madeira vine, Anredera cordifolia (Ten.) Steenis in South Africa." Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005375.
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Anredera cordifolia (Basellaceae), Madeira vine, is a perennial, semi- succulent climber native from Paraguay to southern Brazil and northern Argentina. It has a history of weediness and difficulty of control once established. In South Africa Madeira vine has a wide range and distribution with altitudes ranging from 10-1800m above sea level. Described as a transformer species, its sheer weight is capable of breaking branches off trees, causing the potential collapse of forest canopies. Chemical and mechanical control methods are expensive, labour intensive and may provide only temporary relief. A biological control programme was therefore initiated in 2003. Cf Phenrica sp. 2 (Coleoptera: Chrysomelidae: Alticinae), was field collected from A. cordifolia in Brazil, SSW of Cascavel in the Paraná Province during a survey in November 2003. Eggs are laid in groups of 16 with the average fertility rate being 89%. After going though three larval instars, the larvae pupate in the soil with the adults eclosing after a period of 17 days. The total developmental time for a generation from egg to egg ranges between 7-8 weeks. Biological traits that favour the flea beetle as a possible biological control agent include long-lived adults (up to 5 months) and multiple generations during the summer period. Both adults and larvae feed extensively on leaves and stems and although developmental rates will slow down during the winter period, no indication of a definite diapause was found under the prevailing laboratory conditions. After completing the larval no-choice trials with twenty-six plant species from 14 plant families Phenrica sp. 2 proved to be adequately host specific, as larval development was only supported by 3 Basellaceae species (including the control A. cordifolia) and one Portulacaceae species. All of these are introduced species in South Africa. The only indigenous Basella species could not be tested as it has a very marginal distribution, and because it’s inconspicuous nature, it is seldom seen or collected. Adult multi-choice trials were restricted to species that could sustain larval development to give some indication of the acceptability of these species for adult feeding and oviposition. Although adult feeding was initially concentrated on B. alba, the oviposition preference was clear-cut as females only oviposited on A. cordifolia. In order to quantify the impact of Phenrica sp. 2 on plant biomass and to assess the incidence and intensity of foliar damage, a pair of adults was confined to the host plant, for 2 generations, with different levels of larval densities. The results indicated that the host plant, due to both larval and adult feeding, suffered leaf losses of up to 55%. Anredera cordifolia was however still capable of enlarging the root mass despite suffering huge leaf losses. This would imply that A. cordifolia has an effective re-growth capacity and it will only be vulnerable to attack of the storage organs that enable re-growth, or to repeated attack of other plant parts through which reserves are exhausted. Unfortunately the period of exposure (24 days) was too short to prove that Phenrica sp. 2 impacts on the below ground dry mass, but should the plant be completely defoliated, as was observed in the field, the host plant would be forced to deplete stored resources. Phenrica sp.2 has shown to be very host specific and although A.cordifoia loses its leaves during the winter period in most provinces in South Africa, the adults are long-lived and should be able to survive the leafless periods. Further more the relatively short life cycle, high fecundity and 3 generations per year should theoretically insure a strong population build-up that would improve the chances of establishment in the field. All indications are that Phenrica sp. 2 is an agent well worth considering for the biological control of A. cordifolia.
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Bownes, Angela. "Evaluation of a plant-herbivore system in determining potential efficacy of a candidate biological control agent, cornops aquaticum for water hyacinth, eichhornia crassipes." Thesis, Rhodes University, 2009. http://hdl.handle.net/10962/d1005373.
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Water hyacinth, Eichhornia crassipes Mart. Solms-Laubach (Pontederiaceae), a freefloating aquatic macrophyte of Neotropical origin, was introduced into South Africa as an ornamental aquarium plant in the early 1900’s. By the 1970’s it had reached pest proportions in dams and rivers around the country. Due to the sustainability, cost efficiency and low environmental risk associated with biological control, this has been a widely used method in an attempt to reduce infestations to below the threshold where they cause economic and ecological damage. To date, five arthropod and one pathogen biocontrol agents have been introduced for the control of water hyacinth but their impact has been variable. It is believed that their efficacy is hampered by the presence of highly eutrophic systems in South Africa in which plant growth is prolific and the negative effects of herbivory are therefore mitigated. It is for these reasons that new, potentially more damaging biocontrol agents are being considered for release. The water hyacinth grasshopper, Cornops aquaticum Brüner (Orthoptera: Acrididae), which is native to South America and Mexico, was brought into quarantine in Pretoria, South Africa in 1995. Although the grasshopper was identified as one of the most damaging insects associated with water hyacinth in its native range, it has not been considered as a biocontrol agent for water hyacinth anywhere else in the world. After extensive host-range testing which revealed it to be safe for release, a release permit for this candidate agent was issued in 2007. However, host specificity testing is no longer considered to be the only important component of pre-release screening of candidate biocontrol agents. Investigating biological and ecological aspects of the plant-herbivore system that will assist in determination of potential establishment, efficacy and the ability to build up good populations in the recipient environment are some of the important factors. This thesis is a pre-release evaluation of C. aquaticum to determine whether it is sufficiently damaging to water hyacinth to warrant its release. It investigated interactions between the grasshopper and water hyacinth under a range of nutrient conditions found in South African water bodies as well as the impact of the grasshopper on the competitive performance of water hyacinth. Both plant growth rates and the response of water hyacinth to herbivory by the grasshopper were influenced by nutrient availability to the plants. The ability of water hyacinth to compensate for loss of tissue through herbivory was greater under eutrophic nutrient conditions. However, a negative linear relationship was found between grasshopper biomass and water hyacinth performance parameters such as biomass accumulation and leaf production, even under eutrophic conditions. Water hyacinth’s compensatory ability in terms of its potential to mitigate to detrimental effects of insect feeding was dependent on the amount of damage caused by herbivory by the grasshopper. Plant biomass and the competitive ability of water hyacinth in relation to another freefloating aquatic weed species were reduced by C. aquaticum under eutrophic nutrient conditions, in a short space of time. It was also found that grasshopper feeding and characteristics related to their population dynamics such as fecundity and survival were significantly influenced by water nutrient availability and that environmental nutrient availability will influence the control potential of this species should it be released in South Africa. Cornops aquaticum shows promise as a biocontrol agent for water hyacinth but additional factors that were not investigated in this study such as compatibility with the South African climate and the current water hyacinth biocontrol agents need to be combined with these data to make a decision on its release. Possible management options for this species if it is to be introduced into South Africa are discussed.
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Robertson, Hamish Gibson. "The ecology of Cactoblastis cactorum (Berg) (Lepidoptera : phycitidae) in relation to its effectiveness as a biological control agent of prickly pear and jointed cactus in South Africa." Thesis, Rhodes University, 1985. http://hdl.handle.net/10962/d1005356.
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The successful biological control of the shrub-like prickly pear Opuntia stricta Haworth in Australia by cactoblastis cactorum (Berg) was not repeated when C. cactorum, derived from the Australian population, was released in South Africa in the 1930's against the tree prickly pear Opuntia ficus-indica (L.) Miller. Resistance of the woody portions of o. ficus-indica to attack by C. cactorum was regarded as the main reason for the poor performance of C. cactorum in South Africa. C. cactorum also oviposits and feeds on Opuntia aurantiaca Lindley, which is currently South Africa's most important weed and which is also considered to be partly resistant to attack by C. cactorum. This study had three main objectives: (i) to compare the ecology and effectiveness of C. cactorum as a biological control agent on O. ficusindica and O. aurantiaca; (ii) to reassess why C. cactorum has not been as effective a biological control agent in South Africa as it has been in Australia; and (iii) to evaluate whether inundative release or the importation of new biotypes of C. cactorum from South America (where it is indigenous) might be feasible methods of improving its effectiveness as a biological control agent of O. aurantiaca in South Africa. All field work was undertaken at a site near Grahamstown in South Africa. The ecology and effectiveness of C. cactorum on O. ficus-indica and O. aurantiaca was assessed in terms of its oviposition behaviour, survival and feeding on these host plants. The proportion of C. cactorum eggs laid on O. ficus-indica and O. aurantiaca was similar and was influenced by the size, conspicuousness and condition of the host plant as well as by the proximity of the host plant to moth emergence sites. Factors affecting oviposition site selection on the plant are also considered. Life tables, compiled for a summer and a winter generation, showed that the survival of C. cactorum was greater on O. ficus-indica than on O. aurantiaca, mainly because higher egg predation by ants occurred on the latter host plant species. During the period of study, the population size of C. cactorum was reduced by a number of mortality factors, of which egg predation and the effects of low temperatures on fecundity were the most important. Although there was evidence of a partial, positive response by predatory ants to C. cactorum egg densities on plants, the extent of egg predation was also affected by other factors, particularly seasonal effects. C. cactorum destroyed a greater percentage of cladodes on O. ficu-indica than on O. aurantiaca, but even on O. ficus-indica it was unable to contain the growth of plants within the study area. C. cactorum larvae rarely killed the woody rooted cladodes of O. ficus-indica and O. aurantiaca and consequently whole plants were not often destroyed. The detrimental effects of host plant resistance, natural enemies and climate on the effectiveness of C. cactorum as a biological control agent all appear to be greater in South Africa than in most of the regions occupied by C. cactorum in Australia. A field experiment conducted at the study site showed that inundative release methods for improving the effectiveness of C. cactorum on O. aurantiaca are not feasible. The importation of biotypes of C. cactorum from South America that might be better suited for destroying O. aurantiaca infestations in South Africa, is also not a viable option. Results of a survey of a 218 ha area that is regarded as being heavily infested with O. aurantiaca, illustrate how this cactus species has been overrated as a weed problem. It is argued that the present strategy for O. aurantiaca control in South Africa is not based on sound economic or ecological criteria.
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Baars, Jan-Robert. "Biological control initiatives against Lantana camara L. (Verbenaceae) in South Africa : an assessment of the present status of the programme, and an evaluation of Coelocephalapion camarae Kissinger (Coleoptera: Brentidae) and Falconia intermedia (Distant) (Heteroptera: Miridae), two new candidate natural enemies for release on the weed." Thesis, Rhodes University, 2003. http://hdl.handle.net/10962/d1005329.
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Lantana camara (lantana), a thicket-forming shrub, a number of different varieties of which were introduced into South Africa as ornamental plants but which has become a serious invasive weed. Conventional control measures for lantana are expensive and ineffective and it has therefore been targeted for biological control since 1961. To date, eleven biological control agent species have become established on lantana in South Africa. However, most agents persist at low densities and only occasionally impact plant populations. Three species regularly cause significant damage, but only reach sufficiently high numbers by midsummer after populations crash during the winter. Overall, the impact of the biological control programme on the weed is negligible and this has been ascribed to the poor selection of agents for release, the accumulation of native parasitoids, differences in insect preference for different varieties of the weed and variable climatic conditions over the weed’s range. This study suggests that the importance of varietal preferences has been over-estimated. A predictive bioclimatic modelling technique showed that most of the agents established in South Africa have a wide climatic tolerance and that the redistribution and importation of new climatypes of these agents will not improve the level of control. Additional agents are required to improve the biocontrol in the temperate conditions, and also to increase damage in the sub-tropical areas where most of the agents are established and where the weed retains its leaves year round. New candidate agents that possess biological attributes that favour a high intrinsic rate of increase, a high impact per individual and that improve the synchrony between the weed and the agent in climatic conditions that promote the seasonal leaflessness of plants should receive prior consideration. A survey in Jamaica indicated that additional biological control agents are available in the region of origin but that care should be taken to prioritise the most effective agents. The various selection systems currently available in weed biocontrol produce contradictory results in the priority assigned to candidate agents and a new selection system is proposed. The biology and host range of two new candidate natural enemies, the leaf-galling weevil, Coelocephalapion camarae and the leaf-sucking mirid, Falconia intermedia were investigated for the biocontrol of lantana. The studies indicated that these have considerable biocontrol potential, in that the weevil has a wide climatic tolerance and has the potential to survive the host leaflessness typical of temperate conditions, while the mirid has a high intrinsic rate of increase, and the potential for several generations a year. Both agents caused a high level of damage to the leaves, with the weevil galling the vascular tissue in the leaf-petiole and the mirid causing chlorotic speckling of the leaves. During laboratory trials both agents accepted indigenous species in the genus Lippia. However, under multiple choice conditions these agents showed a significant and strong oviposition preference for lantana. A risk assessment and post release field trials indicated that F. intermedia is likely to attack some Lippia species in the presence of lantana, but the levels of damage are predicted to be relatively low. A possible low incidence of damage to indigenous species was considered a justifiable ‘trade-off’ for the potentially marked impact on L. camara. Preference and performance studies on the two candidate agents suggested that most of the South African lantana varieties are suitable host plants. The mirid preferred certain varieties in multiple choice experiments, but this is unlikely to affect its impact under field conditions. Permission for release was accordingly sought for both species. Finally, the challenges facing the biological control programme and the potential for improving the control of L. camara in South Africa are considered.
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Tourle, Robyn. "Effects of ant predation on the efficacy of biological control agents Hypena Laceratalis Walker (Lepidoptera : noctuirdae) ; Falconia intermedia Distant (Hemiptera : Miridae and Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on Lantana Camara (Verbenaceae) in South Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005362.
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Lantana camara L. (Verbenaceae) remains a highly invasive and ecologically damaging weed in South Africa, despite some 50 years of biological control efforts. Lack of success has been ascribed to varietal differences, climate and predation of agents but these have not been tested. In this study, the effects of ant predation were tested on populations of three biological control agents for L. camara. Colonies of two species, Crematogaster sp. 1 and 2 were investigated. Crematogaster sp. 1 colonies were offered no choice between immature stages of the agents Hypena laceratalis Walker (Lepidoptera: Noctuidae), Falconia intermedia Distant (Hemiptera: Miridae) or Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on lantana shoots. Density-dependent predation on F. intermedia and T. scrupulosa nymphs on lantana shoots was tested using Crematogaster sp. 2 colonies. In choice experiments Crematogaster sp. 2 colonies were offered F. intermedia or T. scrupulosa nymphs on potted lantana plants. Preliminary food trials confirmed that colonies foraged for protein, thereby validating results of no-choice experiments. Crematogaster sp.1 foragers removed 50% of F. intermedia nymphs, followed by 45% of H. laceratalis larvae and only 9% of T. scrupulosa nymphs. Foragers recruited most actively to H. laceratalis larvae and significantly more H. laceratalis biomass was removed than either F. intermedia or T. scrupulosa. A trade-off existed in prey size selection because larger larvae provided considerably more biomass but required forager cooperation and a longer time to subdue than did smaller prey. This increases both forager energy expense and mortality risk by other predators. This study showed that all Crematogaster sp. 1 colonies removed small (≤10mm) H. laceratalis larvae more frequently than larvae larger than 10mm. Thus, of these biological control agents, predators probably prefer small H. laceratalis larvae. Significantly more F. intermedia than T. scrupulosa nymphs were removed by Crematogaster sp. 1, while Crematogaster sp. 2 colonies removed comparable numbers of both agent species. Falconia intermedia nymphs' fast movement triggered a predatory response by these ant species. In contrast, the relatively immobile behaviour of T. scrupulosa nymphs was identified as a highly effective predator avoidance strategy. Since T. scrupulosa nymphs are unable to escape predators by moving, they appear to depend on the presence of alternative prey attracting predator attention. At high agent and/or forager density, T. scrupulosa nymphs attempted escape, but foragers identified them as prey once they moved and caught them. Predation on F. intermedia was also density dependent in that at high nymph and/or forager densities, escape routes were congested and nymphs were more easily caught. Survival of F. intermedia and T. scrupulosa nymphs in particular was low on ant-accessed shrubs in choice experiments and high on ant-excluded shrubs. It is likely that ants significantly depress F. intermedia populations in the field since besides predation, ant foragers probably interrupt F. intermedia feeding and ovipositioning. The combination of parasitism and predation on early instar larvae may explain why H. laceratalis occurs across lantana's range in South Africa but populations remain low. It is unlikely that T. scrupulosa nymphs are habitually preyed on by ant species unless they attract attention by being mobile. Although biological control of L. camara is influenced by climate and physiological defence mechanisms, this study has shown that predation by two ant species severely impacts leaf-feeding agents for L. camara. Thus, it is recommended that future selection of additional agents to control lantana should exclude leaf-feeding .
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Marlin, Danica. "The role of the mite Orthogalumna terebrantis in the biological control programme for water hyacinth, Eichhornia crassipes, in South Africa." Thesis, Rhodes University, 2011. http://hdl.handle.net/10962/d1005450.
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Water hyacinth (Eichhornia crassipes) is an aquatic macrophyte originating from the Amazon basin. Due to its beautiful appearance it has been introduced into numerous countries across the world as an ornamental pond plant. It was introduced into South Africa in the early 1900s and has since reached pest proportions in many of the country’s fresh water bodies, causing significant economic and ecological losses. It is now considered to be the worst aquatic weed in South Africa. Efforts to control the spread of the weed began in the early 1970s and there have been some successes. Biological control has been used widely as an alternative to mechanical and chemical controls because it is cost-effective, self-sustaining and environmentally friendly. To date, six biological control agents have been introduced onto water hyacinth in South Africa. However, due to factors such as cold winter temperatures and interference from chemical control, the agent populations are occasionally knocked-down and thus the impact of biological control on the weed population is variable. In addition, many South African water systems are highly eutrophic, and in these systems the plant growth may be accelerated to such an extent that the negative impact of the agents’ herbivory is mitigated. One of the agents established on the weed is the galumnid mite Orthogalumna terebrantis, which originates from Uruguay. In South Africa, the mite was initially discovered on two water hyacinth infestations in the Mpumalanga Province in 1989 and it is now established at 17 sites across the country. Many biological control researchers believe that the mite is a good biological control agent but, prior to this thesis, little quantitative data existed to confirm the belief. Thus, this thesis is a post-release evaluation of O. terebrantis in which various aspects of the mite-plant relationship were investigated to determine the efficacy of the mite and thus better understand the role of the mite in the biological control programme of water hyacinth in South Africa. From laboratory experiments, in which mite densities were lower than densities occurring in the field, it was found that water hyacinth growth is largely unaffected by mite herbivory, except possibly at very high mite densities. When grown in high nutrient conditions the growth of the plant is so great that any affect the mite has is nullified. Plant growth is thus more affected by nutrients than by mite herbivory. However, mite feeding was also influenced by water nutrient levels and mite herbivory was greatest on plants grown in high nutrient conditions. The presence of the mite had a positive effect on the performance of the mirid Eccritotarsus catarinensis, such that the interactions of the two agents together had a greater negative impact on the plant’s growth than the individual agents had alone. Furthermore, water hyacinth physiological parameters, such as the plant’s photosynthetic ability, were negatively impacted by the mite, even at the very low mite densities used in the study. Plant growth rate is dependent on photosynthetic ability i.e. the rate of photosynthesis, and thus a decrease in the plant’s photosynthetic ability will eventually be translated into decreased plant growth rates which would ultimately result in the overall reduction of water hyacinth populations. In addition, temperature tolerance studies showed that the mite was tolerant of low temperatures. The mite already occurs at some of the coldest sites in South Africa. Therefore, the mite should be able to establish at all of the water hyacinth infestations in the country, but because it is a poor disperser it is unlikely to establish at new sites without human intervention. It is suggested that the mite be used as an additional biological control agent at sites where it does not yet occur, specifically at cold sites where some of the other, less cold-tolerant, agents have failed to establish. Finally, conditions of where, how many and how often the mite should be distributed to water hyacinth infestation in South Africa are discussed.
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Kleinjan, C. A. "The natural enemies of Asparagus asparagoides (L.) Wight in South Africa and their potential for use as biological control agents in Australia." Master's thesis, University of Cape Town, 2000. http://hdl.handle.net/11427/11663.
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Bibliography: leaves 73-76.A form of the southern African plant Asparagus asparagoides (Asparagaceae), is a serious environmental week in Australia, where it is known as bridal creeper. Bridal creeper has an extensive underground tuber system and can invade native vegetation, two factors that make chemical and/or mechanical control difficult. The fruit is bird dispersed which facilitates colonisation of new sites. Surveys for potential biological control agents for use against bridal creeper in Australia were initiated in South Africa during 1989. This dissertation describes the identification, distribution and phenology of A. asparagoides in South Africa, as well as the natural enemies associated with the plant and their potential for use as biological control agents in Australia. Potential biological control agents that attack vegetative growth of bridal creeper included an undescribed Zygina sp. (Cicadellidae), two undescribed Crioceris species (Chrysomelidae - Criocerinae) and the rust fungus, Puccinia myrsiphlli DC. (Uredinales). The seeds of bridal creeper are attacked by an undescribed Eurytoma sp. (Eurytomidae) and the fruits by Zalaca snelleni (Wallengren) (Noctuidae). An organism directly attacking the tuber mass of bridal creeper was not found. Experimental results illustrated that herbivore damage to the above ground parts of the plant resulted in reduced tuber mass and also impacted negatively on fruit production.
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Heshula, Unathi-Nkosi Lelethu Peter. "Induced plant responses of different Lantana camara L. (Verbenaceae) varieties to herbivory by Falconia intermedia (distant) (Hemiptera: Miridae)." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015368.
Full textAbstract:
A highly variable invasive shrub, Lantana camara L. (Verbenaceae), has been notoriously difficult to control thus far despite a well established biological control programme in South Africa. A promising leaf-feeding biological control agent, Falconia intermedia (Distant) (Hemiptera: Miridae), released to control this invasive plant eventually crashed at three out of five sites in the Eastern Cape Province. In the Mpumalanga Province, after initially colonising and building up high numbers on the L. camara stands the agent populations crashed. Several reasons for these population crashes have been suggested, but induced plant defences have not been investigated. Although plants face the challenge of herbivory by various organisms while remaining immobile, some plants may possess the ability to induce physical and/or chemical defensive responses following feeding and thus prevent further plant tissue damage and loss. Laboratory trials were conducted to determine the existence, nature and effect of physical and chemical feeding-induced responses of L. camara on the performance of the leaf-feeding biological control agent, F. intermedia. Lantana camara plants used in the study were obtained from five localities in the Eastern Cape Province, South Africa, while the insect culture was established from field populations. Plants from all varieties on which F. intermedia was released significantly increased the toughness of their leaves compared to control treatment plants. In addition, plants from three localities: Lyndhurst Farm, East London and Port Alfred, significantly increased trichome density after prolonged feeding by F. intermedia. On the three varieties showing increases in these two factors (i.e. leaf toughness and trichome density), oviposition, survival and feeding damage by the mirid agent was significantly lower on previously damaged plants. A significant negative correlation between trichome density and population numbers was found (R²= 0.52, p < 0.0003), suggesting that an increase in trichome density strongly contributes to a reduction in F. intermedia's growth. The growth and reproduction of the resistant plants was not significantly impacted by F. intermedia feeding. The defensive responses were found to be plant systemic and rapidly induced as they were elicited and expressed throughout the plant in both damaged and undamaged leaves within five weeks after insect release. Leaf toughness and trichome density were not significantly increased after feeding on plants from Whitney Farm and Heather Glen Farm. On the contrary, mirid individuals performed significantly better on plants from Whitney Farm and Heather Glen Farm than on plants of other varieties, indicating their susceptibility and suitability to the agent and the lack of induced resistance against the agent. Plants from all localities besides East London showed some level of tolerance and overcompensated for feeding damage by increasing plant growth and reproductive factors on plants fed upon. This was however only significant in two variables of the more susceptible localities, Whitney Farm and Heather Glen Farm. This increase in plant fitness did however indicate an induced defence response by these plants to feeding, a response designed to lessen the effects of agent feeding. Headspace volatile analysis was used to investigate any volatile chemical responses by L. camara due to F. intermedia feeding at two of the five localities chosen: East London and Whitney Farm. There was no significant difference in headspace volatiles emitted by leaves of plants from the East London insect infested and control treatment plants. On the Whitney Farm damaged plants however there was a 2.5 fold increase in the emission intensity of one of the three main compounds, later identified as Beta-caryophyllene. Three major chemical constituents which were found to be common to leaf volatiles of the two varieties were identified through gas chromatography-mass spectrometry (GC-MS) from the damaged and undamaged leaves of these two varieties. The methods used in collecting leaf volatiles were shown to be significant in the strength of chromatogram peaks. Using general authentication methods and purified standards, one of these was identified as the sesquiterpene, Beta-caryophyllene (C₁₅H₂₄). This compound is one of the major constituents found in isolations of L. camara varieties worldwide. This is the first such work done on a variety of L. camara in South Africa, and hopefully the beginning of more in-depth studies of the volatile organic chemicals from the numerous naturalised varieties of L. camara. It is suggested that the sum of these responses may play a role bigger than is currently understood in this plant-insect relationship. It is also argued that feeding induced plant defences may play an important role in attempts to control alien plants using insect agents.
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Kwong, Raelene M., Linda M. Broadhurst, Brian R. Keener, Julie Coetzee, Nunzio Knerr, and Grant D. Martin. "Genetic analysis of native and introduced populations of the aquatic weed Sagittaria platyphylla – implications for biological control in Australia and South Africa." 2017. http://hdl.handle.net/10962/76991.
Full textAbstract:
Sagittaria platyphylla (Engelm.) J.G. Sm. (Alismataceae) is an emergent aquatic plant native to southern USA. Imported into Australia and South Africa as an ornamental and aquarium plant, the species is now a serious invader of shallow freshwater wetlands, slow-flowing rivers, irrigation channels, drains and along the margins of lakes and reservoirs. As a first step towards initiating a classical biological control program, a population genetic study was conducted to determine the prospects of finding compatible biological control agents and to refine the search for natural enemies to source populations with closest genetic match to Australian and South African genotypes. Using AFLP markers we surveyed genetic diversity and population genetic structure in 26 populations from the USA, 19 from Australia and 7 from South Africa. Interestingly, we have established that populations introduced into South Africa and to a lesser extent Australia have maintained substantial molecular genetic diversity comparable with that in the native range. Results from principal coordinates analysis, population graph theory and Bayesian-based clustering analysis all support the notion that introduced populations in Australia and South Africa were founded by multiple sources from the USA. Furthermore, the divergence of some Australian populations from the USA suggests that intraspecific hybridization between genetically distinct lineages from the native range may have occurred. The implications of these findings in relation to biological control are discussed.
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Chauhan, Bhagirath Singh. "Ecology and management of weeds under no-till in southern Australia." 2006. http://hdl.handle.net/2440/37881.
Full textAbstract:
No - till systems have been widely adopted by farmers in Australia over the past decade to reduce soil erosion, improve soil physical and chemical properties, conserve soil moisture and save on fuel costs. These changes in tillage practices can have a major influence on the ecology and management of weeds. Studies were undertaken on the seed biology of six important Australian weed species to provide underpinning knowledge of their response to tillage. Field studies were also undertaken to investigate the effect of no - till on weed seedling emergence, seed bank persistence and herbicide behaviour. Seed germination of threehorn bedstraw and wild turnip, the latter only at sub - optimal temperatures, was inhibited by light. In contrast, seed germination of common sowthistle and Indian hedge mustard was stimulated by light. Seed germination of small - flowered mallow was not influenced by the light conditions. Seedling emergence of threehorn bedstraw, wild turnip, small - flowered mallow and annual ryegrass was low on the soil surface but increased with shallow burial, which suggests that farming practices that achieve shallow burial of seeds are likely to promote greater seedling emergence of these weed species. In contrast, seedling emergence of common sowthistle and Indian hedge mustard was greatest for the seeds present on the soil surface and emergence decreased with increased burial depth. In field experiments, low soil disturbance tillage systems left more seeds on the soil surface after crop sowing, whereas high soil disturbance systems buried most of the seeds. Seedling emergence of annual ryegrass, threehorn bedstraw and wild radish was greater under minimum tillage than no - till system. In contrast, seedling emergence of Indian hedge mustard, common sowthistle, silvergrass, small - flowered mallow and turnipweed was greater under the no - till system. Seedling emergence of wild oat and wild turnip was not influenced by the tillage system. Even though seedling emergence of annual ryegrass was much lower under no - till, the persistence of residual viable seeds of annual ryegrass from one season to the next was similar between the tillage systems. This was because of much greater seed decay under no - till ( 48 to 60 % ) than that recorded under minimum tillage ( 12 to 39 % ). All dinitroaniline herbicides ( trifluralin, pendimethalin and oryzalin ) were more effective in reducing the number of plants, spikes, dry matter and seed production of annual ryegrass when incorporated at sowing with tines than with the discs. At Minlaton in 2004 and 2005, bioavailable trifluralin was greater under tillage systems with greater levels of soil disturbance than under lower soil disturbance systems. In the absence of the herbicide, annual ryegrass was less competitive with wheat under the disc - sown systems. The response of grain yield to herbicides was greater under the tine - sown systems than the disc - sown systems. The performance of S - metolachlor on annual ryegrass control was investigated under no - till. The control of annual ryegrass was greater than 80 % when S - metolachlor was applied at sowing ( incorporated by sowing or post - sowing pre - emergence ). However, application of the herbicide at sowing resulted in phytotoxic effects on crop emergence and grain yield of wheat. Application of S - metolachlor at 20 or 23 days before sowing not only provided effective control ( 74 to 83 % ) of annual ryegrass, it was also safe on wheat. Application of this herbicide at 40 or 46 days before sowing was relatively ineffective in controlling annual ryegrass ( 33 to 49 % weed kill ) but safe on wheat. In conclusion, soil disturbance caused by tillage was found to have a major influence on the behaviour of the seed bank of different species including seedling emergence and decay rates of weed seeds. However, the response to tillage tended to be species - specific and was related to their seed biology. Tillage systems also had a major influence on the efficacy and bioavailability of trifluralin, which is prone to volatilisation losses. The findings of this research program are expected to contribute to the improvement in weed management under no - till systems.Thesis (Ph.D.)--School of Agriculture, Food and Wine, 2006.
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Eslami, Seyed Vahid. "Ecology of wild radish (Raphanus raphanistrum) : crop-weed competition and seed dormancy." 2006. http://hdl.handle.net/2440/59619.
Full textAbstract:
Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library.Field experiments investigating the nature and extent of interference in monocultures and mixtures of wild radish and wheat were conducted in 2003 and 2004 at Roseworthy, South Australia. Intraspecific and interspecific interfenernce between wild radish and wheat was investigated in the field using additive series design. Results indicated that higher densities of wheat were able to suppress seed production of this weed species.
http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1274618
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006
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Katembo, Naweji. "Impact of biocontrol agents on Lantana camara L. (Verbenaceae) in the lowveld region of Mpumalanga, South Africa." Thesis, 2018. https://hdl.handle.net/10539/25839.
Full textAbstract:
A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the academic requirements for the degree of
Doctor of Philosophy
School of Animal, Plant and Environmental Sciences.
Johannesburg, June 2018.Lantana camara L. (sensu lato) (Verbenaceae) remains one of the worst invasive alien plants in most tropical and subtropical parts of the world, including South Africa. Despite a concerted biological control (biocontrol) effort, with 45 biocontrol agents released against the weed worldwide since the early 1900s to date, L. camara control is far from satisfactory in most areas, including the study area. In 2012, during the initial stage of this work, a plant-ecological survey was conducted in riparian areas along the Sabie River, across an altitudinal gradient, and also in the adjacent forest plantation areas, in the province of Mpumalanga (South Africa). As a follow-up to two separate previous studies in the same area (1996/7 and 2005), aimed at determining the effectiveness of the ‘Working for Water’s (WfW) invasive alien plant (IAP) control programme, this work is another milestone in a long-term monitoring study. However, despite 16 years (1996/7-2012) of integrated IAP-control operations in the area, the WfW programme was only able to successfully remove larger overstorey IAPs, which opened-up the canopy and reduced competition, creating a conducive growing environment for an amalgamation of understorey IAPs, including L. camara, whose spread and densification were still on the rise. Biocontrol is regarded as a better alternative for long-term, sustainable and environmentally friendly IAP control, compared to the conventional mechanical and chemical methods. Most L. camara biocontrol agents introduced into South Africa have not yet had their full impact quantified under field conditions. This work is novel in that, for the first time, it quantifies the combined impact of the ‘old plus new’ suite of L. camara biocontrol agents, on the growth, reproduction and biomass of the weed under field conditions, in an inland area, through an insecticidal exclusion experiment, using carbofuran. Five prominent biocontrol agents occur on L. camara at the study sites, namely the fruit-mining fly, Ophiomyia lantanae (Froggatt) (Diptera: Agromyzidae); the shoot-sucking bug, Teleonemia scrupulosa Stål (Hemiptera: Tingidae); the defoliating moth, Hypena laceratalis Walker (Lepidoptera: Noctuidae); the leaf-mining beetle, Octotoma scabripennis Guèrin-Mèneville (Coleoptera: Chrysomelidae); and the fungal leaf-spot pathogen, cf. Passalora sp. (Chupp) U. Braun & Crous var. lantanae. During the course of this study, an additional agent, the flower-galling mite, Aceria lantanae (Cook) (Acari: Trombidiformes: Eriophyidae), was released and successfully established at lower altitudes (~843 m), showing an affinity for the dark-pink L. camara variety over others in the study area, namely light-pink and red-orange. Agent impact was difficult to measure because the activity of carbofuran in exclusion plants (carbofuran-treated L. camara plants) was short-lived; and therefore the impact of biocontrol agents on L. camara, which appeared to be negligible, may have been underestimated. Despite failing to maintain the ‘exclusion’ plants biocontrol agent-free through the application of carbofuran, there were reductions of 28% in the number of side-stems per plant, 31% fewer seeds in the soil seedbank, and 29% lower seed production, in ‘biocontrol’ plants compared to ‘exclusion’ plants. Although these differences were not statistically significant, they suggest that the present suite of biocontrol agents slightly reduces the vegetative and reproductive growth of L. camara. To achieve significant biocontrol of L. camara in inland areas, it seems necessary to introduce additional agents, which are well adapted to inland climatic conditions. The effects of micro-environmental factors, namely altitude and the degree of shading, were also investigated. Some biocontrol agents, such as T. scrupulosa, exhibited feeding phenological plasticity, resulting in it maintaining its presence at different altitudinal levels throughout the seasons. The performance of the suite of biocontrol agents, except A. lantanae, was, also, not limited by plant varietal differences. Additional research on biological and integrated control of L. camara is required. Keywords: Biocontrol; Biological invasion; Carbofuran; Insecticidal exclusion; Invasive alien plants; Lantana camara; Post-release evaluation.
LG2018
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Hill, M. P., and Julie Coetzee. "The biological control of aquatic weeds in South Africa: current status and future challenges." 2017. http://hdl.handle.net/10962/59909.
Full textAbstract:
Aquatic ecosystems in South Africa have been prone to invasion by introduced macrophytes since the late 1800s, when water hyacinth, Eichhornia crassipes (Mart.) Solms-Laub. (Pontederiaceae), was first recorded as naturalised in KwaZulu-Natal (Cilliers 1991). Several other species of freshwater aquatic plants, all notorious weeds in other parts of the world, have also become invasive in many of the rivers, man-made impoundments, lakes and wetlands of South Africa (Hill 2003). These are Pistia stratiotes L. (Araceae) (water lettuce); Salvinia molesta D.S. Mitch. (Salviniaceae) (salvinia); Myriophyllum aquaticum (Vell. Conc.) Verd. (parrot's feather); and Azolla filiculoides Lam. (Azollaceae) (red water fern) (Hill 2003), which along with water hyacinth comprise the 'Big Bad Five' (Henderson & Cilliers 2002). Recently, new invasive aquatic plant species have been recorded which are still at their early stages of invasion, including the submerged species, Egeria densa Planch. (Hydrocharitaceae) (Brazilian water weed) and Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae); the emergent species, Sagittaria platyphylla (Engelm.) J.G.Sm. and S. latifolia Willd. (Alismataceae); Lythrum salicaria L. (Lythraceae) (purple loosestrife), Nasturtium officinale W.T. Aiton. (Brassicaceae) (watercress); Iris pseudacorus L. (Iridaceae) (yellow flag); and Hydrocleys nymphoides (Humb. & Bonpl. ex Willd.) Buchenau (Alismataceae) (water poppy); and the new floating weeds, Salvinia minima Baker (Salviniaceae) and Azolla cristata Kaulf. (Azollaceae) (Mexican azolla); and the rooted floating Nymphaea mexicana Zucc. (Nymphaeceae) (Mexican water lily) (Coetzee et al. 2011a; Coetzee, Bownes & Martin 2011b). The mode of introduction of these species is mainly through the horticultural and aquarium trade (Martin & Coetzee 2011), and two issues contribute to the invasiveness of these macrophytes following establishment: the lack of co-evolved natural enemies in their adventive range (McFadyen 1998); and disturbance, the presence of nitrate- and phosphate-enriched waters, associated with urban, agricultural and industrial pollution that promotes plant growth (Coetzee & Hill 2012).
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Kitt, Jörg Thomas. "Introduction of Aphidius rosae into Australia for biological control of the rose aphid (Macrosiphum rosae)." 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phk608.pdf.
Full textAbstract:
Bibliography: leaves 221-240. This thesis deals with the introduction of "Aphidius rosae" as a classical biological control agent into South-Eastern Australia. Appropriate host specificity tests are carried out. Laboratory experiments are also completed to gain a better understanding of the interactions between host and parasitoid in the field. The study aims to monitor the performance of the control agent in the Adelaide environment for the first two years after initial release. It is also planned to invent an experimental field technique to estimate the impact of the control agent on rose aphid populations.
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Kitt, Jorg Thomas. "Introduction of Aphidius rosae into Australia for biological control of the rose aphid (Macrosiphum rosae) / by Jorg Thomas Kitt." 1996. http://hdl.handle.net/2440/18781.
Full textAbstract:
Bibliography: leaves 221-240.viii, 240, [13] leaves : ill. (some col.), maps ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
This thesis deals with the introduction of "Aphidius rosae" as a classical biological control agent into South-Eastern Australia. Appropriate host specificity tests are carried out. Laboratory experiments are also completed to gain a better understanding of the interactions between host and parasitoid in the field. The study aims to monitor the performance of the control agent in the Adelaide environment for the first two years after initial release. It is also planned to invent an experimental field technique to estimate the impact of the control agent on rose aphid populations.
Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1997
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Cowie, Blair William. "Bugweed biocontrol: new insights into the biological control agents of Solanum mauritianum, Gargaphia decoris and Anthonomus santacruzi." Thesis, 2016. http://hdl.handle.net/10539/21676.
Full textAbstract:
A Dissertation submitted to the Faculty of Science, University of the Witwatersrand,
in partial fulfilment of the requirements for the degree of Master of Science,
Johannesburg, South Africa. 2016.Solanum mauritianum Scopoli (Solanaceae) is a perennial tree or shrub native to South America, which has become a prominent and widespread invader in numerous sub-tropical countries around the world. In South Africa, S. mauritianum is listed as one of the country’s worst ecological weeds, having been targeted for biological control efforts since 1984. Despite some constraints, biocontrol efforts have seen the successful release of two promising biocontrol agents. The first of these biocontrol agents, released against S. mauritianum, was the sap-sucking lace bug, Gargaphia decoris Drake (Hemiptera: Tingidae). Sap-feeding by G. decoris metabolically impaired the leaves, resulting in a reduction to their photosynthesis, with a greater effect on plants growing in full-sun compared to plants growing in the shade. This difference was attributed to higher leaf temperatures experienced in the sun. Herbivory reduced transpiration rates by more than 50%, resulting in a reduction in evaporative cooling of the leaf. The increased physiological damage experienced by full-sun plants may be a combination of stresses, particularly the direct effect of chlorophyll removal via herbivory and the indirect effect of accumulated heat–light stress. The flowerbud-feeding weevil, Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), was released in 2008 as a biological control agent against S. mauritianum. The hypothesis that climate, particularly low temperature and low relative humidity, restricts the survival and establishment of A. santacruzi in South Africa was tested. Thermal assessments on A. santacruzi adults calculated the CTmin and LT50 as 4.1 ± 0.2 °C (n = 20) and 4.2 ± 0.3 °C (n = 90) respectively. The LH50 of A. santacruzi adults was calculated as 46.9%. The establishment of A. santacruzi at only the warm and humid release sites in South Africa advocates for the consideration of low temperature and low humidity as factors impeding the agents’ establishment and spread, particularly on the cooler and drier Highveld. Furthermore, the impact of A. santacruzi’s florivory on the reproductive output of S. mauritianum, as well as the potential of the agent to act as an indirect pollinator was assessed. Overall direct floral damage caused by A. santacruzi was trivial, with only ~5% of the anther and ~2% of the petal area being removed. However, the consequent effects of A. santacruzi were considerably more damaging, with 25% and 66% reductions in flowering and fruiting respectively. Additionally, fruits produced from inflorescences exposed to A. santacruzi were smaller in size, with fewer, less viable seeds. The feeding and presence of A. santacruzi also maintains the potential for indirect effects on the pollination of S. mauritianum. This suggests that in areas with well-established A. santacruzi populations, the weevils may simultaneously facilitate the self-pollination and potential inbreeding of S. mauritianum. Keywords: Agent impacts and effects; biological control; Bugweed; climatic unsuitability; ecophysiology; indirect effects; post-release evaluation.
LG2017
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King, Anthony Michael. "The effect of temperature on biological control of water hyacinth, Eichhornia crassipes (Pontederiaceae) in South Africa." Thesis, 2012. http://hdl.handle.net/10539/11066.
Full textAbstract:
MSc., Faculty of Science, University of the Witwatersrand, 2011The behaviour and physiology of every insect, during all developmental stages, is largely determined by temperature. Metabolic rate, flight activity, nutrition, growth rate, oviposition and longevity can all be correlated to temperature. Consequently, insect development occurs within a definite temperature range which can be experimentally determined. This serves as a basis from which models that estimate insect growth, development and reproduction can be formulated. Such studies on temperature-dependent development are therefore important for understanding predator-prey relationships and insect population dynamics relevant in epidemiology, pest management and biological control of weeds and insect pests. The biological control of water hyacinth, Eichhornia crassipes (Pontederiaceae), in South Africa currently relies on six established agents. However, the results of this programme do not compare well with the achievements made elsewhere. This has been attributed to a number of constraining factors, chief among which is a wide variety of climatic regions, low minimum temperatures and a high incidence of frosting which slows the build-up of natural enemy populations. This research verified and augmented the thermal tolerance data available for three of South Africa’s more efficacious agents used against water hyacinth, namely Neochetina eichhorniae, N. bruchi (Curculionidae) and Eccritotarsus catarinensis (Miridae). Using these data, plant productivity and insect activity was modelled against fine-scale temperature data incorporating three distinct microclimates from 14 field sites distributed throughout South Africa’s climatic regions. Water hyacinth and its natural enemies were found to be negatively affected by low average temperatures. However, the relative consequences for each species at a population level were quite different. Similar thresholds for development, close to 10°C, meant that periods available for growth in areas where temperature is limiting were roughly the same for both plant and insects. Nevertheless, although plant growth largely ceased each winter and aerial parts were often extensively damaged from frost, low temperatures rarely led to significant plant mortality. By contrast, reduced insect recruitment coupled with a high susceptibility to cold- and frost-induced mortality of all life-history stages, pushed insect populations into winter bottlenecks and even caused local extinctions. The ability to overwinter effectively appears to the primary cause for limited control in colder regions. Surviving post-winter insect populations were therefore small, inflicted minimal damage due to reduced feeding rates, and were generally asynchronous with the recovery of water hyacinth. This asynchronous development translated into a lag period of roughly 42 days between the onset of water hyacinth growth and the time at which the plant was subjected to meaningful herbivory. Free from early season herbivory, coupled with the fact that vegetative reproduction continued through winter, water hyacinth populations were able to quickly recover and outpaced the detrimental affects caused by insect feeding well into the growth season. The implications for supplementary management strategies are also discussed in light of these outcomes.
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Oberholzer, Izak Gerhardus. "The effect of nutrient rich water on the biological control of water hyacinth." Diss., 2002. http://hdl.handle.net/2263/28536.
Full textAbstract:
Please read the abstract on p1 of the document 00dissertationDissertation (M Inst Agrar (Sustainable Insect Management))--University of Pretoria, 2007.
Zoology and Entomology
M Inst Agrar
unrestricted
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Craemer, Charnie. "Eriophyidae (Acari) as potential control agents of South African weeds, with descriptions of a new species of Tegonotus nalepa and of Paraphytoptus nalepa." Thesis, 2014. http://hdl.handle.net/10210/9776.
Full textAbstract:
M.Sc. (Zoology)This study centres around the findings on mites (Acari: Eriophyidae) (also referred to as "eriophyids") as potential biological control agents of weeds in South Africa. The use of mites in the biological control of weeds is briefly reviewed. Four species of the family Eriophyidae have been used against weeds in other countries. Seventeen eriophyid species, causing symptoms possibly of significance to biological weed control of 12 plant species regarded as weeds in South Africa, are discussed. Methods to rear and study eriophyids in the laboratory have not yet been fully developed and studying these practically invisible arthropods, very closely associated with their host plants, frequently presents difficulties. Reported methods, and those used for the present study, are reviewed and discussed. The eriophyid, Aceria lantanae (Cook), causing flower and leaf galls on Lantana camara L. could not be successfully established in a quarantine laboratory on potted plants propagated from cuttings of L. camara forms from South Africa. The results obtained during this attempt were inconclusive. The failure of establishment on local L. camara forms could be attributed to a variety of factors, of which rearing methods and host incompatibility are the most likely. Convolvulus arvensis is a troublesome agricultural weed and occurs in especially the Orange Free State and the eastern and southern parts of the Cape Province. Biological control may possibly contribute to curbing this weed in South Africa. The eriophyid, Aceria malherbae Nuzzaci, causing deformation and galling on C. arvensis is regarded as one of the most promising candidates for the biological control of this weed. It was imported and successfully established on potted plants in a quarantine laboratory on biotypes of the weed occurring in South Africa. The biology and host specificity of A malherbae are accounted for, by using reported information and data obtained during this study. The biology of A. malherbae broadly conforms to the biology of other eriophyid species. This species has a narrow host range, being restricted to species very closely related to C. arvensis. The symptoms caused by this eriophyid on C. arvensis are described, and seem especially harmful to the reproductive potential of the plant. Two eriophyid species from L. camara from Paraguay, Tegonotus stefneseri and Paraphytoptus magdalenae, are described as new species. An illustrated as well as a dichotomous key to species (Eriophyoidea) described from L. camara, including the two new species, are provided. A key, and a review of known Tegonotus species, incorporated in a compendium based on the original descriptions of 74 species, are included. Shevtchenkella Bagdasarian is considered to be a junior subjective synonym of Tegonotus Nalepa.
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Kokkinn, M. J. (Michael J. ). "A control strategy for `Tanytarsus barbitarsis` Freeman (Diptera : Chironomidae), a small-scale pest organism / M.J. Kokkinn." 1986. http://hdl.handle.net/2440/20989.
Full textAbstract:
Bibliography: leaves 214-235iv, 235 leaves : ill ; 30 cm.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, Dept. of Zoology, 1987
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Paull, Cate. "The ecology of key arthropods for the management of Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae) in Coonawarra vineyards, South Australia." 2008. http://hdl.handle.net/2440/47971.
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There is currently little knowledge about the dynamics of invertebrates in Australian viticultural ecosystems. This study was conducted in Coonawarra vineyards over three seasons (years) and has focused on identifying natural enemies, their seasonal phenology, multiple species interactions, and potential for the suppression of the pest lepidopteran Epiphyas postvittana (Tortricidae). The work presented in this thesis shows that endemic natural enemies have far greater potential to control E. postvittana than has been realised. An initial survey identified a diverse and abundant range of potential natural enemies. Of these, the species most likely to attack E. postvittana include a predatory mite Anystis baccarum and a number of hymenopteran parasitoids. The most abundant parasitoid in the vineyards was a braconid, Dolichogenidea tasmanica. Understanding the characteristic behaviour of parasitoids in response to host density can help to gauge their potential for pest suppression. The results of large-scale field experiments showed that the response of D. tasmanica to the density of E. postvittana was inversely density-dependent, and that parasitism was consistently higher in Cabernet Sauvignon compared with Chardonnay varieties. Despite the fact that interactions among multiple species of natural enemies can increase or decrease pest suppression, particularly when they share a common prey/host, few multispecies interactions have been investigated. Laboratory studies identified a novel interaction between the predatory mite A. baccarum an abundant predator in the vine canopy, the parasitoid D. tasmanica and host E. postvittana larvae. Although A. baccarum readily ate E. postvittana eggs and free roaming larvae, they could not access larva in their silk leaf rolls. However, the addition of D. tasmanica significantly increased predation of E. postvittana larvae, by altering the behaviour of host larvae and increasing their vulnerability to the mite. Experiments conducted at a landscape level in the Coonawarra showed that D. tasmanica was also present in habitat other than vineyards including native vegetation. However, it was not present in highly disturbed habitats. Although the exact mechanism for this remains unknown, results indicate that viticultural practices and resources in the surrounding landscape can influence the presence of parasitoids. Together, the findings presented in this thesis make a significant contribution towards developing sustainable pest management in Australian viticulture.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1320930
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008
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Van, der Westhuizen Liamé. "The evaluation of Phenrica sp. 2 (Coleoptera: Chrysomelidae: Alticinae), as a possible biological control agent for Madeira vine, Anredera cordifolia (Ten.) Steenis in South Africa /." 2006. http://eprints.ru.ac.za/496/.
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