A study on the application technology of the sterile insect technique, with focus on false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a pest of citrus in South Africa
- Authors: Nepgen, Eugene Stephan
- Date: 2014
- Subjects: Cryptophlebia leucotreta , Citrus -- Diseases and pests -- Control -- South Africa , Insect pests -- Control -- South Africa , Insect sterilization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5879 , http://hdl.handle.net/10962/d1013199
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is considered the most important indigenous pest of citrus in southern Africa. Major concerns such as progressive insecticidal resistance, the negative impact of insecticides on the environment, as well as the influence of consumers opposed to chemical residues on fruit, created opportunities for biological control methods such as Sterile Insect Technology (SIT). This technology is now established in the Western and Eastern Cape provinces of South Africa as an effective, sustainable alternative to conventional FCM control methods. Due to the prevalence of the pest in all citrus producing areas of South Africa, potential for SIT to expand is enormous. Success of an SIT programme is highly dependent on efficient application of the technology to achieve its objectives in a timeous manner. The aim of this study was to advance the application of SIT for control of FCM on citrus in South Africa, by investigating the effect of certain critical stages in the process. The effect of long-distance transportation on fitness of irradiated FCM was determined, showing reduced performance with cold-immobilized transport. A significant decrease in flight ability and longevity of irradiated FCM was found, although critically, realized fecundity was not affected. The effect of two different insecticides in the pyrethroid and organophosphate chemical groups were investigated for their residual effect on mortality of released irradiated FCM, to determine if these pest control programmes could be integrated. Both chlorpyrifos and tau-fluvalinate were effective in killing irradiated FCM for a number of days after application, after which degradation of the active ingredient rendered it harmless. This effect was found to be similar for irradiated and non-irradiated males, consequently ratios of sterile : wild male FCM should be retained regardless of whether sprays are applied or not. The modes for release of sterile FCM in an SIT programme were investigated. Efficacy of ground and aerial release platforms were tested by evaluating the recovery of released irradiated male FCM in these orchards. More irradiated FCM were recovered in orchards released from the ground compared to air. However, an economic analysis of both methods shows application of irradiated insects over a large geographical area is more cost-effective by air. Depending on the terrain and size of the target area, a combination of both methods is ideal for application of SIT for control of FCM in citrus. Development of application technology for advance of the programme is discussed and recommendations for future research and development are offered.
- Full Text:
- Authors: Nepgen, Eugene Stephan
- Date: 2014
- Subjects: Cryptophlebia leucotreta , Citrus -- Diseases and pests -- Control -- South Africa , Insect pests -- Control -- South Africa , Insect sterilization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5879 , http://hdl.handle.net/10962/d1013199
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is considered the most important indigenous pest of citrus in southern Africa. Major concerns such as progressive insecticidal resistance, the negative impact of insecticides on the environment, as well as the influence of consumers opposed to chemical residues on fruit, created opportunities for biological control methods such as Sterile Insect Technology (SIT). This technology is now established in the Western and Eastern Cape provinces of South Africa as an effective, sustainable alternative to conventional FCM control methods. Due to the prevalence of the pest in all citrus producing areas of South Africa, potential for SIT to expand is enormous. Success of an SIT programme is highly dependent on efficient application of the technology to achieve its objectives in a timeous manner. The aim of this study was to advance the application of SIT for control of FCM on citrus in South Africa, by investigating the effect of certain critical stages in the process. The effect of long-distance transportation on fitness of irradiated FCM was determined, showing reduced performance with cold-immobilized transport. A significant decrease in flight ability and longevity of irradiated FCM was found, although critically, realized fecundity was not affected. The effect of two different insecticides in the pyrethroid and organophosphate chemical groups were investigated for their residual effect on mortality of released irradiated FCM, to determine if these pest control programmes could be integrated. Both chlorpyrifos and tau-fluvalinate were effective in killing irradiated FCM for a number of days after application, after which degradation of the active ingredient rendered it harmless. This effect was found to be similar for irradiated and non-irradiated males, consequently ratios of sterile : wild male FCM should be retained regardless of whether sprays are applied or not. The modes for release of sterile FCM in an SIT programme were investigated. Efficacy of ground and aerial release platforms were tested by evaluating the recovery of released irradiated male FCM in these orchards. More irradiated FCM were recovered in orchards released from the ground compared to air. However, an economic analysis of both methods shows application of irradiated insects over a large geographical area is more cost-effective by air. Depending on the terrain and size of the target area, a combination of both methods is ideal for application of SIT for control of FCM in citrus. Development of application technology for advance of the programme is discussed and recommendations for future research and development are offered.
- Full Text:
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
- Authors: Stafford, Martha Louise
- Date: 2014
- Subjects: Aquatic weeds -- South Africa -- Cape Town , Aquatic weeds -- Biological control -- South Africa -- Cape Town , Water hyacinth -- Biological control -- South Africa -- Cape Town , Metropolitan areas -- South Africa -- Cape Town
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5874 , http://hdl.handle.net/10962/d1013015
- Description: 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.
- Full Text:
- Authors: Stafford, Martha Louise
- Date: 2014
- Subjects: Aquatic weeds -- South Africa -- Cape Town , Aquatic weeds -- Biological control -- South Africa -- Cape Town , Water hyacinth -- Biological control -- South Africa -- Cape Town , Metropolitan areas -- South Africa -- Cape Town
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5874 , http://hdl.handle.net/10962/d1013015
- Description: 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.
- Full Text:
Genetic and biological characterisation of a novel South African Plutella xylostella granulovirus (PlxyGV) isolate
- Authors: Abdulkadir, Fatima
- Date: 2014
- Subjects: Diamondback moth , Diamondback moth -- Control -- South Africa , Plutellidae -- Control -- South Africa , Baculoviruses , Cruciferae -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4113 , http://hdl.handle.net/10962/d1013059
- Description: The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is an important pest of cruciferous crops worldwide. The prolonged use of synthetic chemical insecticides as a primary means of control has resulted in the development of resistance in pest populations. In addition, the pest has also evolved resistance to the bacterial insecticidal protein of Bacillus thuringiensis which is also widely used as a method of control. Baculoviruses are considered as effective alternatives to conventional methods of control when incorporated into integrated pest management (IPM) programmes. These viruses target the larval stages of insects, are generally host-specific and are safe for use in the environment. This study aimed to isolate a baculovirus from a laboratory-reared P. xylostella colony, characterise it genetically and then evaluate its virulence against neonate and fourth instar larvae. A laboratory colony of P. xylostella was established using pupae and asymptomatic larvae collected from a cabbage plantation outside Grahamstown in the Eastern Cape province of South Africa. The colony flourished in the laboratory due to prime conditions and availability of food. The duration of development from egg to adult was determined by observation and imaging of the various life stages. The mean developmental time from egg to adult was observed to be 14.59 ± 0.21 days. The population of the insects increased rapidly in number leading to overcrowding of the insect colony, and hence appearance of larvae with viral symptoms. Occlusion bodies (OBs) were extracted from symptomatic larval cadavers and purified by glycerol gradient centrifugation. Analysis of the purified OBs by transmission electron microscopy revealed the presence of a granulovirus which was named PlxyGV-SA. The virus isolate was genetically characterised by restriction endonuclease analysis of the genomic DNA, and PCR amplification and sequencing of selected viral genes. The complete genome sequence of a Japanese P. xylostella granulovirus isolate, PlxyGV-Japan, has been deposited on the GenBank database providing a reference strain for comparison with DNA profiles and selected gene sequences of PlxyGV-SA. BLAST analysis of the granulin gene confirmed the isolation of a novel South African PlxyGV isolate. Comparison of the restriction profiles of PlxyGV-SA with profiles of PlxyGV-Japan and other documented PlxyGV profiles obtained by agarose gel electrophoresis revealed that PlxyGV-SA is a genetically distinct isolate. The data obtained from the sequencing and alignment of ecdysteroid UDP-glucosyltransferase (egt), late expression factor 8 (lef-8) and late expression factor 9 (lef-9) genes with those of PlxyGV-Japan also showed that PlxyGV-SA is a genetically different isolate. In order to determine the biological activity of PlxyGV-SA against neonate and fourth instar P. xylostella larvae, surface dose bioassays were conducted. The median lethal concentration of the virus required to kill 50% (LC₅₀) and 90% (LC₉₀) of the larvae was estimated by feeding insects with a range of doses. In addition, the time to kill 50% of the larvae (LT₅₀) was determined by feeding insects with the LC₉₀ concentration. Larval mortality was monitored daily until pupation. The data obtained from the dose response assays were subjected to probit analysis using Proban statistical software. The time response was determined using GraphPad Prism software (version 6.0). The LC₅₀ and LC₉₀ values for the neonate larvae were 3.56 × 10⁵ and 1.14 × 10⁷ OBs/ml respectively. The LT₅₀ was determined to be 104 hours. The neonate larvae were found to be more susceptible to infection than the fourth instar larvae with the same virus concentration. The concentrations used for the neonate larvae assay did not have a significant effect on the fourth instar as no mortality was recorded. This is the first study to describe a novel South African PlxyGV isolate and the results suggest that PlxyGV-SA has significant potential for development as an effective biopesticide for the control of P. xylostella in the field.
- Full Text:
- Authors: Abdulkadir, Fatima
- Date: 2014
- Subjects: Diamondback moth , Diamondback moth -- Control -- South Africa , Plutellidae -- Control -- South Africa , Baculoviruses , Cruciferae -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4113 , http://hdl.handle.net/10962/d1013059
- Description: The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is an important pest of cruciferous crops worldwide. The prolonged use of synthetic chemical insecticides as a primary means of control has resulted in the development of resistance in pest populations. In addition, the pest has also evolved resistance to the bacterial insecticidal protein of Bacillus thuringiensis which is also widely used as a method of control. Baculoviruses are considered as effective alternatives to conventional methods of control when incorporated into integrated pest management (IPM) programmes. These viruses target the larval stages of insects, are generally host-specific and are safe for use in the environment. This study aimed to isolate a baculovirus from a laboratory-reared P. xylostella colony, characterise it genetically and then evaluate its virulence against neonate and fourth instar larvae. A laboratory colony of P. xylostella was established using pupae and asymptomatic larvae collected from a cabbage plantation outside Grahamstown in the Eastern Cape province of South Africa. The colony flourished in the laboratory due to prime conditions and availability of food. The duration of development from egg to adult was determined by observation and imaging of the various life stages. The mean developmental time from egg to adult was observed to be 14.59 ± 0.21 days. The population of the insects increased rapidly in number leading to overcrowding of the insect colony, and hence appearance of larvae with viral symptoms. Occlusion bodies (OBs) were extracted from symptomatic larval cadavers and purified by glycerol gradient centrifugation. Analysis of the purified OBs by transmission electron microscopy revealed the presence of a granulovirus which was named PlxyGV-SA. The virus isolate was genetically characterised by restriction endonuclease analysis of the genomic DNA, and PCR amplification and sequencing of selected viral genes. The complete genome sequence of a Japanese P. xylostella granulovirus isolate, PlxyGV-Japan, has been deposited on the GenBank database providing a reference strain for comparison with DNA profiles and selected gene sequences of PlxyGV-SA. BLAST analysis of the granulin gene confirmed the isolation of a novel South African PlxyGV isolate. Comparison of the restriction profiles of PlxyGV-SA with profiles of PlxyGV-Japan and other documented PlxyGV profiles obtained by agarose gel electrophoresis revealed that PlxyGV-SA is a genetically distinct isolate. The data obtained from the sequencing and alignment of ecdysteroid UDP-glucosyltransferase (egt), late expression factor 8 (lef-8) and late expression factor 9 (lef-9) genes with those of PlxyGV-Japan also showed that PlxyGV-SA is a genetically different isolate. In order to determine the biological activity of PlxyGV-SA against neonate and fourth instar P. xylostella larvae, surface dose bioassays were conducted. The median lethal concentration of the virus required to kill 50% (LC₅₀) and 90% (LC₉₀) of the larvae was estimated by feeding insects with a range of doses. In addition, the time to kill 50% of the larvae (LT₅₀) was determined by feeding insects with the LC₉₀ concentration. Larval mortality was monitored daily until pupation. The data obtained from the dose response assays were subjected to probit analysis using Proban statistical software. The time response was determined using GraphPad Prism software (version 6.0). The LC₅₀ and LC₉₀ values for the neonate larvae were 3.56 × 10⁵ and 1.14 × 10⁷ OBs/ml respectively. The LT₅₀ was determined to be 104 hours. The neonate larvae were found to be more susceptible to infection than the fourth instar larvae with the same virus concentration. The concentrations used for the neonate larvae assay did not have a significant effect on the fourth instar as no mortality was recorded. This is the first study to describe a novel South African PlxyGV isolate and the results suggest that PlxyGV-SA has significant potential for development as an effective biopesticide for the control of P. xylostella in the field.
- Full Text:
Screening of entomopathogenic fungi against citrus mealybug (Planococcus citri (Risso)) and citrus thrips (Scirtothrips aurantii (Faure))
- FitzGerald, Véronique Chartier
- Authors: FitzGerald, Véronique Chartier
- Date: 2014
- Subjects: Entomopathogenic fungi , Citrus mealybug -- South Africa -- Eastern Cape , Citrus thrips -- South Africa -- Eastern Cape , Citrus -- Diseases and pests , Citrus mealybug -- Biological control , Citrus thrips -- Biological control , Biological pest control agents , Scanning electron microscopy , Mycoses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4166 , http://hdl.handle.net/10962/d1020887
- Description: Mealybugs (Planococcus citri) and thrips (Scirtothrips aurantii) are common and extremely damaging citrus crop pests which have proven difficult to control via conventional methods, such as chemical pesticides and insect growth regulators. The objective of this study was to determine the efficacy of entomopathogenic fungi against these pests in laboratory bioassays. Isolates of Metarhizium anisopliae and Beauveria bassiana from citrus orchards in the Eastern Cape, South Africa were maintained on Sabouraud Dextrose 4% Agar supplemented with Dodine, chloramphenicol and rifampicin at 25°C. Infectivity of the fungal isolates was initially assessed using 5th instar false codling moth, Thaumatotibia leucotreta, larvae. Mealybug bioassays were performed in 24 well plates using 1 x 107 ml-1 conidial suspensions and kept at 26°C for 5 days with a photoperiod of 12 L:12 D. A Beauveria commercial product and an un-inoculated control were also screened for comparison. Isolates GAR 17 B3 (B. bassiana) and FCM AR 23 B3 (M. anisopliae) both resulted in 67.5% mealybug crawler mortality and GB AR 23 13 3 (B. bassiana) resulted in 64% crawler mortality. These 3 isolates were further tested in dose-dependent assays. Probit analyses were conducted on the dose-dependent assays data using PROBAN to determine LC₅₀ values. For both the mealybug adult and crawlers FCM AR 23 B3 required the lowest concentration to achieve LC₅₀ at 4.96 x 10⁶ conidia ml-1 and 5.29 x 10⁵ conidia ml-1, respectively. Bioassays on adult thrips were conducted in munger cells with leaf buds inoculated with the conidial suspensions. Isolate GAR 17 B3 had the highest mortality rate at 70% on thrips while FCM AR 23 B3 resulted in 60% mortality. Identification of the isolates, FCM AR 23 B3, GAR 17 B3 and GB AR 23 13 3, were confirmed to be correct using both microscopic and molecularly techniques. ITS sequences were compared to other sequences from GenBank and confirmed phylogenetically using MEGA6. Mealybug infection was investigated using scanning electron microscopy, mycosis was confirmed but the infection process could not be followed due to the extensive waxy cuticle. These results indicate that there is potential for the isolates FCM AR 23 B3 and GAR 17 B3 to be developed as biological control agents for the control of citrus mealybug and thrips. Further research would be required to determine their ability to perform under field conditions.
- Full Text:
- Authors: FitzGerald, Véronique Chartier
- Date: 2014
- Subjects: Entomopathogenic fungi , Citrus mealybug -- South Africa -- Eastern Cape , Citrus thrips -- South Africa -- Eastern Cape , Citrus -- Diseases and pests , Citrus mealybug -- Biological control , Citrus thrips -- Biological control , Biological pest control agents , Scanning electron microscopy , Mycoses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4166 , http://hdl.handle.net/10962/d1020887
- Description: Mealybugs (Planococcus citri) and thrips (Scirtothrips aurantii) are common and extremely damaging citrus crop pests which have proven difficult to control via conventional methods, such as chemical pesticides and insect growth regulators. The objective of this study was to determine the efficacy of entomopathogenic fungi against these pests in laboratory bioassays. Isolates of Metarhizium anisopliae and Beauveria bassiana from citrus orchards in the Eastern Cape, South Africa were maintained on Sabouraud Dextrose 4% Agar supplemented with Dodine, chloramphenicol and rifampicin at 25°C. Infectivity of the fungal isolates was initially assessed using 5th instar false codling moth, Thaumatotibia leucotreta, larvae. Mealybug bioassays were performed in 24 well plates using 1 x 107 ml-1 conidial suspensions and kept at 26°C for 5 days with a photoperiod of 12 L:12 D. A Beauveria commercial product and an un-inoculated control were also screened for comparison. Isolates GAR 17 B3 (B. bassiana) and FCM AR 23 B3 (M. anisopliae) both resulted in 67.5% mealybug crawler mortality and GB AR 23 13 3 (B. bassiana) resulted in 64% crawler mortality. These 3 isolates were further tested in dose-dependent assays. Probit analyses were conducted on the dose-dependent assays data using PROBAN to determine LC₅₀ values. For both the mealybug adult and crawlers FCM AR 23 B3 required the lowest concentration to achieve LC₅₀ at 4.96 x 10⁶ conidia ml-1 and 5.29 x 10⁵ conidia ml-1, respectively. Bioassays on adult thrips were conducted in munger cells with leaf buds inoculated with the conidial suspensions. Isolate GAR 17 B3 had the highest mortality rate at 70% on thrips while FCM AR 23 B3 resulted in 60% mortality. Identification of the isolates, FCM AR 23 B3, GAR 17 B3 and GB AR 23 13 3, were confirmed to be correct using both microscopic and molecularly techniques. ITS sequences were compared to other sequences from GenBank and confirmed phylogenetically using MEGA6. Mealybug infection was investigated using scanning electron microscopy, mycosis was confirmed but the infection process could not be followed due to the extensive waxy cuticle. These results indicate that there is potential for the isolates FCM AR 23 B3 and GAR 17 B3 to be developed as biological control agents for the control of citrus mealybug and thrips. Further research would be required to determine their ability to perform under field conditions.
- Full Text:
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