The biology, behaviour and survival of pupating false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a citrus pest in South Africa
- Authors: Love, Claire Natalie
- Date: 2015
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Larvae -- Behavior , Citrus -- Diseases and pests , Citrus -- Diseases and pests -- Biological control , Biological pest control agents , Entomopathogenic fungi , Insect nematodes , Pupae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5941 , http://hdl.handle.net/10962/d1018907
- Description: Control of the citrus pest, false codling moth (FCM), Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is crucial for the South African citrus industry. The economic losses and phytosanitary status of this pest, coupled with increased consumer awareness and demands, has created a need for effective, IPM-compatible control measures for use against the soil-dwelling life stages of FCM. Promising developments in the field of microbial control through the use of entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPNs) have highlighted the need for research regarding pupation biology, behaviour and survival of FCM, as a good understanding of biology of the target organism is an important component of any biological control programme. The aim of this study was to improve the current understanding of FCM pupation habits through the manipulation of soil texture class, ground cover, shading, soil compaction, air temperature, and soil moisture in the laboratory. These findings would then be used to aid the biological control programmes using EPF and EPNs against FCM in the soil. Three soil texture classes (sandy loam, silt loam and silty clay loam) were obtained from orchards for use in the study. FCM larvae were allowed to drop into the soil of their own accord and the pupation behaviour that followed was then captured on film with pupae formed in the soil being kept in order to measure adult eclosion. In general, very few abiotic factors had a clear influence on FCM pupation. Larval wandering time and distance was short, but also variable between individuals. Distance did increase when soils were moist. Pupation depth was shallow, with pupal cocoons generally being formed on the soil surface. Depth of pupation was less than one centimetre for all abiotic conditions, with little burrowing into soil. Eclosion success was higher for sandier soils when these were dry and uncompacted, but the addition of both moisture and soil compaction increased FCM eclosion success. FCM was sensitive to desiccation when the soils were dry and temperature limits of 15 °C and 32 °C had a strongly negative impact on eclosion success. Preferences for particular abiotic conditions were limited to only certain moisture conditions when interacting with soil texture class and a preference for pupating in soil when it is available. Limited preference was found for particular soil textures despite this having a strong influence on eclosion success, but individuals did appear to pupate in close proximity to one another. Viable direct habitat manipulation for FCM control could not be identified. These results and all of the abiotic variables measured have important implications for EPF and EPN application, survival and persistence in the soil in order to improve the ability of these biological control agents to control FCM. These are discussed in each chapter.
- Full Text:
- Date Issued: 2015
- Authors: Love, Claire Natalie
- Date: 2015
- Subjects: Cryptophlebia leucotreta -- South Africa , Cryptophlebia leucotreta -- Larvae -- Behavior , Citrus -- Diseases and pests , Citrus -- Diseases and pests -- Biological control , Biological pest control agents , Entomopathogenic fungi , Insect nematodes , Pupae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5941 , http://hdl.handle.net/10962/d1018907
- Description: Control of the citrus pest, false codling moth (FCM), Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae) is crucial for the South African citrus industry. The economic losses and phytosanitary status of this pest, coupled with increased consumer awareness and demands, has created a need for effective, IPM-compatible control measures for use against the soil-dwelling life stages of FCM. Promising developments in the field of microbial control through the use of entomopathogenic fungi (EPF) and entomopathogenic nematodes (EPNs) have highlighted the need for research regarding pupation biology, behaviour and survival of FCM, as a good understanding of biology of the target organism is an important component of any biological control programme. The aim of this study was to improve the current understanding of FCM pupation habits through the manipulation of soil texture class, ground cover, shading, soil compaction, air temperature, and soil moisture in the laboratory. These findings would then be used to aid the biological control programmes using EPF and EPNs against FCM in the soil. Three soil texture classes (sandy loam, silt loam and silty clay loam) were obtained from orchards for use in the study. FCM larvae were allowed to drop into the soil of their own accord and the pupation behaviour that followed was then captured on film with pupae formed in the soil being kept in order to measure adult eclosion. In general, very few abiotic factors had a clear influence on FCM pupation. Larval wandering time and distance was short, but also variable between individuals. Distance did increase when soils were moist. Pupation depth was shallow, with pupal cocoons generally being formed on the soil surface. Depth of pupation was less than one centimetre for all abiotic conditions, with little burrowing into soil. Eclosion success was higher for sandier soils when these were dry and uncompacted, but the addition of both moisture and soil compaction increased FCM eclosion success. FCM was sensitive to desiccation when the soils were dry and temperature limits of 15 °C and 32 °C had a strongly negative impact on eclosion success. Preferences for particular abiotic conditions were limited to only certain moisture conditions when interacting with soil texture class and a preference for pupating in soil when it is available. Limited preference was found for particular soil textures despite this having a strong influence on eclosion success, but individuals did appear to pupate in close proximity to one another. Viable direct habitat manipulation for FCM control could not be identified. These results and all of the abiotic variables measured have important implications for EPF and EPN application, survival and persistence in the soil in order to improve the ability of these biological control agents to control FCM. These are discussed in each chapter.
- Full Text:
- Date Issued: 2015
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:
- Date Issued: 2014
- 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:
- Date Issued: 2014
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