An evaluation of the effects of imported insects on the weed Lantana camara L. in South Africa
- Authors: Cilliers, Catharina Johanna
- Date: 1982
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5808 , http://hdl.handle.net/10962/d1006853
- Description: The plant, Lantana camara L. (V erbenaceae), is a weed in tropical and subtropical areas around the world. In many countries, including South Africa, biological control of this weed has been attempted. Although 12 insect species have been imported into South Africa, only four species established and these are dealt with in this study. Ophiomyia lantanae Diptera: Agromyzidae, a seed fly, is briefly dealt with; the main emphasis is on the leaf damaging species Teleonemia scrupulosa Stål (Hemiptera: Tingidae) and two leaf mining beetles, Octotoma scabripennis Guerin and Uroplata girardi Pic . (Hispidae: Coleoptera). In evaluating the insect damage to lantana leaves, monthly samples of branches were taken over three seasons from 1977- 80. This destructive sampling allowed the study of population build-up of the insects. In addition, counts were made of the numbers of damaged and healthy leaves, flowers and seeds and the damage related to the activities of the different stages of the hispids and the tingid. Insect exclusion experiments were also used to determine the effect of the insects on the growth of L. camara. The results reported in this thesis clearly indicate that the imported natural enemies retard L. camara growth and vigour and the effects are manifested in a marked reduction in stem diameter, internodal length, leaf size, leaf lifespan and in flower and seed set.
- Full Text:
- Date Issued: 1982
- Authors: Cilliers, Catharina Johanna
- Date: 1982
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5808 , http://hdl.handle.net/10962/d1006853
- Description: The plant, Lantana camara L. (V erbenaceae), is a weed in tropical and subtropical areas around the world. In many countries, including South Africa, biological control of this weed has been attempted. Although 12 insect species have been imported into South Africa, only four species established and these are dealt with in this study. Ophiomyia lantanae Diptera: Agromyzidae, a seed fly, is briefly dealt with; the main emphasis is on the leaf damaging species Teleonemia scrupulosa Stål (Hemiptera: Tingidae) and two leaf mining beetles, Octotoma scabripennis Guerin and Uroplata girardi Pic . (Hispidae: Coleoptera). In evaluating the insect damage to lantana leaves, monthly samples of branches were taken over three seasons from 1977- 80. This destructive sampling allowed the study of population build-up of the insects. In addition, counts were made of the numbers of damaged and healthy leaves, flowers and seeds and the damage related to the activities of the different stages of the hispids and the tingid. Insect exclusion experiments were also used to determine the effect of the insects on the growth of L. camara. The results reported in this thesis clearly indicate that the imported natural enemies retard L. camara growth and vigour and the effects are manifested in a marked reduction in stem diameter, internodal length, leaf size, leaf lifespan and in flower and seed set.
- Full Text:
- Date Issued: 1982
Evaluation of Tucumania Tapiacola Dyar (Lepidoptera: Phycitidae) for biological control of jointed cactus in South Africa
- Authors: Hoffmann, John Hugh
- Date: 1982
- Subjects: Phycitidae Cactus -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5634 , http://hdl.handle.net/10962/d1005316
- Description: Jointed cactus, 0puntia aurantiaca Lindley, remains a problem and continues to expand its range in South Africa, in spite of a mandatory herbicidal control. programme. The feasibility of biologically controlling the weed is being explored because the cost of herbicides has escalated and, if it succeeds, biological control is permanent self perpetuating and relatively cheap. This thesis describes the introduction and release in South Africa of the phycitid moth, Tucumania tapiacola Dyar, as a potential biocontrol agent against jointed cactus. A preliminary objective of the study was to resolve the taxonomic confusion within the genus Tucumania, so that the various populations of the moth from widespread localities and from different host plants could be identified. The efficiency of mass-producing T. tapiacola in the insectary was continually improved through investigations of the insects biology, and its response to various environmental parameters. Techniques were developed to manipulate the different life-stages of T. tapiacola so that every release was made with the maximum possible number of individuals, all in the same stage of development. Trials were made with various methods for transporting and releasing T. tapiacola in the field, and the most successful of these were employed during the establishment programme. In all, approximately 830 000 T. tapiacola eggs, larvae and adults have been released at seven localities in South Africa, between May 1977 and February 1982. So far, the moth has failed to establish for more than three to five generations at any release site, for reasons that were not immediately apparent. The mortality factors acting against the immature stages of T. tapiacola have been investigated and quantified. The accumulated data were used to construct partial-life-tables and survivorship curves. These show that survival of the eggs, larvae and pupae differed in shaded and exposed habitats, and on small, medium and large O. aurantiaca plants. The overall mortality suffered by the immature stages alone did not account for the establishment failure. Alternatively, genetic problems that are commonly associated with the collection, mass production and release of biocontrol agents may have been responsible for the failure. Methods of overcoming these problems during future releases are discussed.
- Full Text:
- Date Issued: 1982
- Authors: Hoffmann, John Hugh
- Date: 1982
- Subjects: Phycitidae Cactus -- South Africa Weeds -- Biological control -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5634 , http://hdl.handle.net/10962/d1005316
- Description: Jointed cactus, 0puntia aurantiaca Lindley, remains a problem and continues to expand its range in South Africa, in spite of a mandatory herbicidal control. programme. The feasibility of biologically controlling the weed is being explored because the cost of herbicides has escalated and, if it succeeds, biological control is permanent self perpetuating and relatively cheap. This thesis describes the introduction and release in South Africa of the phycitid moth, Tucumania tapiacola Dyar, as a potential biocontrol agent against jointed cactus. A preliminary objective of the study was to resolve the taxonomic confusion within the genus Tucumania, so that the various populations of the moth from widespread localities and from different host plants could be identified. The efficiency of mass-producing T. tapiacola in the insectary was continually improved through investigations of the insects biology, and its response to various environmental parameters. Techniques were developed to manipulate the different life-stages of T. tapiacola so that every release was made with the maximum possible number of individuals, all in the same stage of development. Trials were made with various methods for transporting and releasing T. tapiacola in the field, and the most successful of these were employed during the establishment programme. In all, approximately 830 000 T. tapiacola eggs, larvae and adults have been released at seven localities in South Africa, between May 1977 and February 1982. So far, the moth has failed to establish for more than three to five generations at any release site, for reasons that were not immediately apparent. The mortality factors acting against the immature stages of T. tapiacola have been investigated and quantified. The accumulated data were used to construct partial-life-tables and survivorship curves. These show that survival of the eggs, larvae and pupae differed in shaded and exposed habitats, and on small, medium and large O. aurantiaca plants. The overall mortality suffered by the immature stages alone did not account for the establishment failure. Alternatively, genetic problems that are commonly associated with the collection, mass production and release of biocontrol agents may have been responsible for the failure. Methods of overcoming these problems during future releases are discussed.
- Full Text:
- Date Issued: 1982
The ecology and control of Opuntia Aurantiaca in South Africa in relation to the cochineal insect, Dactylopius Austrinus
- Authors: Zimmermann, Helmuth G
- Date: 1982
- Subjects: Cochineal insect -- South Africa Cactus -- South Africa Weeds -- Control -- South Africa Insect-plant relationships
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5612 , http://hdl.handle.net/10962/d1003061
- Description: The cochineal insect Dactylopius austrinus De Lotto, which was released on jointed cactus, Opuntia aurantiaca Lindley, in South Africa in 1932, failed to bring the weed under an acceptable level of control in spite of the encouraging results during the first few years after release. The reasons for this apparent failure were never clearly understood. In 1957 the State embarked on an intensive herbicidal control programme which is still in force today. This sustained and expensive programme has undoubtedly reduced the density of the weed in most areas but has failed to solve the problem and the plant continues to expand its range. The biological control of o. aurantiaca in South Africa has been fundamentally influenced by this chemical control campaign. The relationship between chemical and biological control methods is reported in this study.
- Full Text:
- Date Issued: 1982
- Authors: Zimmermann, Helmuth G
- Date: 1982
- Subjects: Cochineal insect -- South Africa Cactus -- South Africa Weeds -- Control -- South Africa Insect-plant relationships
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5612 , http://hdl.handle.net/10962/d1003061
- Description: The cochineal insect Dactylopius austrinus De Lotto, which was released on jointed cactus, Opuntia aurantiaca Lindley, in South Africa in 1932, failed to bring the weed under an acceptable level of control in spite of the encouraging results during the first few years after release. The reasons for this apparent failure were never clearly understood. In 1957 the State embarked on an intensive herbicidal control programme which is still in force today. This sustained and expensive programme has undoubtedly reduced the density of the weed in most areas but has failed to solve the problem and the plant continues to expand its range. The biological control of o. aurantiaca in South Africa has been fundamentally influenced by this chemical control campaign. The relationship between chemical and biological control methods is reported in this study.
- Full Text:
- Date Issued: 1982
The Karoo caterpillar Loxostege Frustalis Zeller (Lepidoptera : Pyralidae) in relation to its host plants and natural enemies
- Authors: Möhr, Johann Diederich
- Date: 1982
- Subjects: Caterpillars -- South Africa Lepidoptera -- Host plants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5604 , http://hdl.handle.net/10962/d1002054
- Description: The Karoo is an arid inland plateau in the central and northeastern Cape Province of South Africa and is characterised by sparse, stunted vegetation. The vegetation is rich in species, and over large areas species of Pentzia, which are drought-resistant shrubs, are extremely abundant. These plants are food for stock (mainly sheep), and because the larvae of the Karoo caterpillar periodically occur in sufficient numbers to defoliate the plants, they assume pest status. Fully-fed Loxostege frustalis larvae construct cases in the soil beneath their food plants and they overwinter in these cases. A census of the numbers of larval cases accumulated in the soil, conducted from 1975 to 1980, showed that an expanded distribution of the pentzias is responsible for the periodic larval outbreaks. Further, alternate food plants are an important food supply for L. frustalis larvae when they disperse under crowded conditions The census data for L. frustalis were analysed by constructing partial life tables for the life-history period from case construction to moth emergence. The mortality of 'encased larvae' is useful for assessing the impact of the known L. frustalis natural enemies. The most important natural enemies were the braconids Chelonus curvimaculatus Cameron, Macrocentrus maraisi Nixon and the fungus Beauveria bassiana (Balsamo) Vuillemin. The collective responses of all the natural enemies to the density of L. frustalis encased larvae was direct, but undercompensating, so that areas with more pentzias produced more L. frustais. Strategies for immediate measures to alleviate the Karoo caterpillar problem, and for future research, are discussed. It is concluded that reduction of pentzia populations to acceptable levels and/or supplementing pastures with non-host plants of L. frustalis offer the only practical solutions to the Karoo caterpillar problem. Biological control of L. frustalis is dismissed as an option for reducing the pest status of the Karoo caterpillar
- Full Text:
- Date Issued: 1982
- Authors: Möhr, Johann Diederich
- Date: 1982
- Subjects: Caterpillars -- South Africa Lepidoptera -- Host plants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5604 , http://hdl.handle.net/10962/d1002054
- Description: The Karoo is an arid inland plateau in the central and northeastern Cape Province of South Africa and is characterised by sparse, stunted vegetation. The vegetation is rich in species, and over large areas species of Pentzia, which are drought-resistant shrubs, are extremely abundant. These plants are food for stock (mainly sheep), and because the larvae of the Karoo caterpillar periodically occur in sufficient numbers to defoliate the plants, they assume pest status. Fully-fed Loxostege frustalis larvae construct cases in the soil beneath their food plants and they overwinter in these cases. A census of the numbers of larval cases accumulated in the soil, conducted from 1975 to 1980, showed that an expanded distribution of the pentzias is responsible for the periodic larval outbreaks. Further, alternate food plants are an important food supply for L. frustalis larvae when they disperse under crowded conditions The census data for L. frustalis were analysed by constructing partial life tables for the life-history period from case construction to moth emergence. The mortality of 'encased larvae' is useful for assessing the impact of the known L. frustalis natural enemies. The most important natural enemies were the braconids Chelonus curvimaculatus Cameron, Macrocentrus maraisi Nixon and the fungus Beauveria bassiana (Balsamo) Vuillemin. The collective responses of all the natural enemies to the density of L. frustalis encased larvae was direct, but undercompensating, so that areas with more pentzias produced more L. frustais. Strategies for immediate measures to alleviate the Karoo caterpillar problem, and for future research, are discussed. It is concluded that reduction of pentzia populations to acceptable levels and/or supplementing pastures with non-host plants of L. frustalis offer the only practical solutions to the Karoo caterpillar problem. Biological control of L. frustalis is dismissed as an option for reducing the pest status of the Karoo caterpillar
- Full Text:
- Date Issued: 1982
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