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
- Authors: Tourle, Robyn
- Date: 2010
- Subjects: Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5677 , http://hdl.handle.net/10962/d1005362 , Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Description: 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 .
- Full Text:
- Authors: Tourle, Robyn
- Date: 2010
- Subjects: Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5677 , http://hdl.handle.net/10962/d1005362 , Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Description: 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 .
- Full Text:
Laboratory and field host utilization by established biological control agents of Lantana camara L. in South Africa
- Authors: Heystek, Fritz
- Date: 2006
- Subjects: Lantana camara -- South Africa , Biological pest control agents -- South Africa , Weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5725 , http://hdl.handle.net/10962/d1005411 , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Description: Varieties of Lantana camara (lantana) have been introduced into many countries of the world as ornamental plants and have become invasive weeds in many countries including South Africa. In South Africa, it mostly invades the sub-tropical eastern and northern range. Mechanical and chemical control options are expensive and ineffective. A biocontrol programme was initiated in South Africa in 1961. To date, 22 insect species, and a fungus have been introduced, of these 10, and the fungus have established. Three indigenous lepidopteran species and an exotic generalist pest mealybug are also associated with the weed. The variable success of some of the agents released on L. camara worldwide has been ascribed to a few factors. One important aspect is the large range of varieties encountered in the field. It is therefore essential to be able to predict the possible establishment and impact of agents on many varieties. Laboratory trials on five of the established agents showed clear varietal preferences. In the field, most of the biocontrol agents had limited geographic ranges, linked to altitudinal conditions, as higher populations were recorded at low lying warm summer rainfall areas. A pink and orange flower corolla lobe and throat colour combination and plants with few to medium leaf hairs were most abundant in South Africa. Most of the agent species had individual preferences towards different flower colour combinations, as the agents built up different population levels on varieties in the field, within the suitable geographic region for the insect species. Eight agents preferred smooth leaved varieties, while three preferred hairy leaves, and three had no specific preference to leaf hairiness. Varietal preferences thus did play a significant role in agent populations and accompanied impact achieved in the field. New candidate agents need to be proven specific under quarantine conditions and the results extrapolated to predict specificity in the field, while avoiding potential non-target effects. Many authors have questioned the validity of laboratory host specificity trials. The conventional wisdom is that insects portray a far wider host range in the laboratory than what they would do in the field. In other words, laboratory studies measure the physiological host range of an agent and are conservative and usually don’t reflect the ecological host range of agents in the field. To avoid unnecessary rejections of biocontrol agents, this study has made a retrospective study of the host specificity of agents established in the field. Their laboratory and field host ranges were compared and it was found that virtually all the agents reflect similar or less non-target effects in the field than predicted during multiple choice trials. Of the 14 agents, only one introduced species, Teleonemia scrupulosa, and the indigenous species, Hypena laceratalis and Aristea onychote were able to sustain populations on non-target species in the field in the absence of L. camara. Insect populations on non-target species were much reduced compared to that on L. camara. Furthermore non-target effects were only recorded on plant species closely related to the target weed. The multiple choice trials therefore predict field non-target effects accurately. Predictions of non-target effects of candidate agents can therefore be accurately predicted by laboratory studies, in terms of species likely to be affected and to what extent. One field that need further study though is the impact of non-target effects, especially on Lippia species by L. camara biocontrol agents.
- Full Text:
- Authors: Heystek, Fritz
- Date: 2006
- Subjects: Lantana camara -- South Africa , Biological pest control agents -- South Africa , Weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5725 , http://hdl.handle.net/10962/d1005411 , Lantana camara -- South Africa , Biological pest control agents -- South Africa , Weeds -- Biological control -- South Africa , Invasive plants -- Biological control -- South Africa
- Description: Varieties of Lantana camara (lantana) have been introduced into many countries of the world as ornamental plants and have become invasive weeds in many countries including South Africa. In South Africa, it mostly invades the sub-tropical eastern and northern range. Mechanical and chemical control options are expensive and ineffective. A biocontrol programme was initiated in South Africa in 1961. To date, 22 insect species, and a fungus have been introduced, of these 10, and the fungus have established. Three indigenous lepidopteran species and an exotic generalist pest mealybug are also associated with the weed. The variable success of some of the agents released on L. camara worldwide has been ascribed to a few factors. One important aspect is the large range of varieties encountered in the field. It is therefore essential to be able to predict the possible establishment and impact of agents on many varieties. Laboratory trials on five of the established agents showed clear varietal preferences. In the field, most of the biocontrol agents had limited geographic ranges, linked to altitudinal conditions, as higher populations were recorded at low lying warm summer rainfall areas. A pink and orange flower corolla lobe and throat colour combination and plants with few to medium leaf hairs were most abundant in South Africa. Most of the agent species had individual preferences towards different flower colour combinations, as the agents built up different population levels on varieties in the field, within the suitable geographic region for the insect species. Eight agents preferred smooth leaved varieties, while three preferred hairy leaves, and three had no specific preference to leaf hairiness. Varietal preferences thus did play a significant role in agent populations and accompanied impact achieved in the field. New candidate agents need to be proven specific under quarantine conditions and the results extrapolated to predict specificity in the field, while avoiding potential non-target effects. Many authors have questioned the validity of laboratory host specificity trials. The conventional wisdom is that insects portray a far wider host range in the laboratory than what they would do in the field. In other words, laboratory studies measure the physiological host range of an agent and are conservative and usually don’t reflect the ecological host range of agents in the field. To avoid unnecessary rejections of biocontrol agents, this study has made a retrospective study of the host specificity of agents established in the field. Their laboratory and field host ranges were compared and it was found that virtually all the agents reflect similar or less non-target effects in the field than predicted during multiple choice trials. Of the 14 agents, only one introduced species, Teleonemia scrupulosa, and the indigenous species, Hypena laceratalis and Aristea onychote were able to sustain populations on non-target species in the field in the absence of L. camara. Insect populations on non-target species were much reduced compared to that on L. camara. Furthermore non-target effects were only recorded on plant species closely related to the target weed. The multiple choice trials therefore predict field non-target effects accurately. Predictions of non-target effects of candidate agents can therefore be accurately predicted by laboratory studies, in terms of species likely to be affected and to what extent. One field that need further study though is the impact of non-target effects, especially on Lippia species by L. camara biocontrol agents.
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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
- Authors: Van der Westhuizen, Liamé
- Date: 2006
- Subjects: Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Invasive plants -- Biological control -- South Africa , Chrysomelidae , Beetles , Flea beetles , Anredera cordifolia -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5689 , http://hdl.handle.net/10962/d1005375 , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Invasive plants -- Biological control -- South Africa , Chrysomelidae , Beetles , Flea beetles , Anredera cordifolia -- Biological control
- Description: 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.
- Full Text:
- Authors: Van der Westhuizen, Liamé
- Date: 2006
- Subjects: Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Invasive plants -- Biological control -- South Africa , Chrysomelidae , Beetles , Flea beetles , Anredera cordifolia -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5689 , http://hdl.handle.net/10962/d1005375 , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Invasive plants -- Biological control -- South Africa , Chrysomelidae , Beetles , Flea beetles , Anredera cordifolia -- Biological control
- Description: 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.
- Full Text:
The biological control of Hakea sericea Schrader by the Hakea seed-moth, Carposina autologa Meyrick, in South Africa
- Authors: Gordon, Antony John
- Date: 1993
- Subjects: Weeds -- Biological control -- South Africa , Moths , Carposinidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5648 , http://hdl.handle.net/10962/d1005330 , Weeds -- Biological control -- South Africa , Moths , Carposinidae
- Description: 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.
- Full Text:
- Authors: Gordon, Antony John
- Date: 1993
- Subjects: Weeds -- Biological control -- South Africa , Moths , Carposinidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5648 , http://hdl.handle.net/10962/d1005330 , Weeds -- Biological control -- South Africa , Moths , Carposinidae
- Description: 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.
- Full Text:
An evaluation of Mimorista pulchellalis (Dyar) (Lepidoptera : Pyraustidae) as a biocontrol agent against jointed cactus in South Africa
- Authors: Nieman, Erik
- Date: 1984
- Subjects: Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5812 , http://hdl.handle.net/10962/d1007052 , Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Description: From the introduction: The work on Mimorista is divided into two sections: a laboratory orientated study which describes the biology and rearing techniques and a field orientated study where the establishment of the insect and its impact on jointed cactus populations are examined. In the final chapters the integration of this insect in the current control program are discussed and recommendations regarding its future in South Africa are given.
- Full Text:
- Authors: Nieman, Erik
- Date: 1984
- Subjects: Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5812 , http://hdl.handle.net/10962/d1007052 , Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Description: From the introduction: The work on Mimorista is divided into two sections: a laboratory orientated study which describes the biology and rearing techniques and a field orientated study where the establishment of the insect and its impact on jointed cactus populations are examined. In the final chapters the integration of this insect in the current control program are discussed and recommendations regarding its future in South Africa are given.
- Full Text:
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