An evaluation of the socio-economic costs and benefits of the invasive Rubus (Blackberry/Bramble) genus at selected sites in South Africa
- Authors: Mason, Brett Anthony
- Date: 2021-10-29
- Subjects: Rubus South Africa Cost effectiveness , Invasive plants South Africa Cost effectiveness , Rubus Economic aspects South Africa , Ecology Economic aspects South Africa , Rubus Ecology South Africa , Environmental economics South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/191931 , vital:45180
- Description: Rubus L. (brambles, blackberries, raspberries, or dewberries) are a globally recognised genus due to the edible fruit and negative impacts they can have as invasive species. There are at least 23 species of Rubus subgenus Rubus in South Africa. These include native, alien, naturalised alien, and invasive alien species. The invasive Rubus species are becoming an increasing problem in South Africa with experts in invasion biology urging caution regarding the genus (Henderson, 2011). The taxonomy of indigenous, alien and alien invasive species of Rubus are poorly understood and therefore efforts to understand the genus, the impacts and solutions to those impacts have been very limited (Stirton, 1981; Henderson, 2011; Sochor et al., 2018a). There has also been little research conducted on the economic or ecological impacts on the species or genus of species in South Africa (du Plessis et al., 1984; Botha, 2005), and yet species in the genus have been earmarked for prioritization by invasive species legislation. The potential value of certain species as well as the cost associated with their impacts could potentially create a complex conflict of interest scenario which has not been investigated. This study is an effort to inform future policy decisions regarding this suite of species by investigating the economic impacts of the invasive Rubus species. A method was developed unique to the study that incorporated research tools from environmental economics and geography to identify the nature of interactions between economic agents, experts, and alien and invasive Rubus species in South Africa. Two questionnaires were developed to generate economic data and ground proofing was used to develop geographic data. One questionnaire was directed specifically at researchers and academics that attended the 46th National Symposium on Biological Invasions that took place between 15–17 May 2019, at Waterval Country Lodge, Tulbagh and the other an economic agent questionnaire for economic agents that met strict and selective criteria relating to the impact of the six invasive Rubus species on their economic activity. Both questionnaires were designed with a mixed methods approach in mind. The ground proofing was aimed at understanding the composition and distribution of Rubus species at the selected sites: Cathcart and Hogsback (The Eastern Cape Province), Clarens (Free State Province), and Underberg (KwaZulu-Natal Province). The study established that all economic impacts of invasive Rubus species at selected sites are externalities. Invasive Rubus species in South Africa can be attributed as (i) harbouring vermin, (ii) impeding human and animal livestock, (iii) reducing crop yields, (iv) encroaching on grazing land, (v) presenting fire hazards, and (vi) negatively impacting fire regimes. These species also (i) provide berries that are retailed on a commercial level, or have been, (ii) that are utilized for personal consumption, (iii) provide an ingredient for alcohol brewing processes, and (iv) could potentially facilitate forest regeneration. The invasive species are infrequently browsed by certain livestock and far as we could ascertain do not provide ingredients for anti-inflammatory drugs or modern cosmetics in South Africa, as they do in other regions of the globe. The costs associated with the invasive species can be presented dichotomously; the estimated private cost-benefit ratio, for costs and benefits incurred or enjoyed by 18 private economic agents, stands at 0.33:1. A private-public benefit-cost ratio, that incorporates both private and public costs and benefits, stands at 13,5:1. The private-public benefit-cost includes public expenditure, or government control measures, directed at invasive Rubus and shifts the benefit-cost ratio so that costs now markedly dominate the estimated benefits. The benefits per hectare uncovered in this study stand at R13.14/ha. The private costs stand at R4.32/ha and a holistic cost, including both private and public expenditure, stands at R177,43/ha. The monetary values, when expressed per hectare, are misleading. This is due to a large standard deviation in the spread of benefits received. The benefits are enjoyed by a small number of the already small sample of respondents. The costs and benefits are not uniformly distributed across regions assessed. All benefits in this study accrue to economic agents in the Free State Province, whilst most of the costs accrued to economic agents in KwaZulu-Natal Province. The benefits appear to be primarily derived from an alien species, Rubus sect. Arguti. Management of the 6 species of invasive Rubus could be optimised by the prioritisation of those regions that incur the highest cost and derive the lowest benefit, in this case KwaZulu-Natal Province. Likewise, those regions with the highest benefits and lowest costs, the Free State Province, could provide sites for increased use and beneficiation of berries from invasive species. Management of individual species may prove difficult, given the similar morphologies, and thus, (i) either specialised training for those engaged in control must be instituted, (ii) all species of alien Rubus should be earmarked for management, or (iii) highly specific biocontrol agents for the most problematic species must be found. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2021
- Full Text:
- Authors: Mason, Brett Anthony
- Date: 2021-10-29
- Subjects: Rubus South Africa Cost effectiveness , Invasive plants South Africa Cost effectiveness , Rubus Economic aspects South Africa , Ecology Economic aspects South Africa , Rubus Ecology South Africa , Environmental economics South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/191931 , vital:45180
- Description: Rubus L. (brambles, blackberries, raspberries, or dewberries) are a globally recognised genus due to the edible fruit and negative impacts they can have as invasive species. There are at least 23 species of Rubus subgenus Rubus in South Africa. These include native, alien, naturalised alien, and invasive alien species. The invasive Rubus species are becoming an increasing problem in South Africa with experts in invasion biology urging caution regarding the genus (Henderson, 2011). The taxonomy of indigenous, alien and alien invasive species of Rubus are poorly understood and therefore efforts to understand the genus, the impacts and solutions to those impacts have been very limited (Stirton, 1981; Henderson, 2011; Sochor et al., 2018a). There has also been little research conducted on the economic or ecological impacts on the species or genus of species in South Africa (du Plessis et al., 1984; Botha, 2005), and yet species in the genus have been earmarked for prioritization by invasive species legislation. The potential value of certain species as well as the cost associated with their impacts could potentially create a complex conflict of interest scenario which has not been investigated. This study is an effort to inform future policy decisions regarding this suite of species by investigating the economic impacts of the invasive Rubus species. A method was developed unique to the study that incorporated research tools from environmental economics and geography to identify the nature of interactions between economic agents, experts, and alien and invasive Rubus species in South Africa. Two questionnaires were developed to generate economic data and ground proofing was used to develop geographic data. One questionnaire was directed specifically at researchers and academics that attended the 46th National Symposium on Biological Invasions that took place between 15–17 May 2019, at Waterval Country Lodge, Tulbagh and the other an economic agent questionnaire for economic agents that met strict and selective criteria relating to the impact of the six invasive Rubus species on their economic activity. Both questionnaires were designed with a mixed methods approach in mind. The ground proofing was aimed at understanding the composition and distribution of Rubus species at the selected sites: Cathcart and Hogsback (The Eastern Cape Province), Clarens (Free State Province), and Underberg (KwaZulu-Natal Province). The study established that all economic impacts of invasive Rubus species at selected sites are externalities. Invasive Rubus species in South Africa can be attributed as (i) harbouring vermin, (ii) impeding human and animal livestock, (iii) reducing crop yields, (iv) encroaching on grazing land, (v) presenting fire hazards, and (vi) negatively impacting fire regimes. These species also (i) provide berries that are retailed on a commercial level, or have been, (ii) that are utilized for personal consumption, (iii) provide an ingredient for alcohol brewing processes, and (iv) could potentially facilitate forest regeneration. The invasive species are infrequently browsed by certain livestock and far as we could ascertain do not provide ingredients for anti-inflammatory drugs or modern cosmetics in South Africa, as they do in other regions of the globe. The costs associated with the invasive species can be presented dichotomously; the estimated private cost-benefit ratio, for costs and benefits incurred or enjoyed by 18 private economic agents, stands at 0.33:1. A private-public benefit-cost ratio, that incorporates both private and public costs and benefits, stands at 13,5:1. The private-public benefit-cost includes public expenditure, or government control measures, directed at invasive Rubus and shifts the benefit-cost ratio so that costs now markedly dominate the estimated benefits. The benefits per hectare uncovered in this study stand at R13.14/ha. The private costs stand at R4.32/ha and a holistic cost, including both private and public expenditure, stands at R177,43/ha. The monetary values, when expressed per hectare, are misleading. This is due to a large standard deviation in the spread of benefits received. The benefits are enjoyed by a small number of the already small sample of respondents. The costs and benefits are not uniformly distributed across regions assessed. All benefits in this study accrue to economic agents in the Free State Province, whilst most of the costs accrued to economic agents in KwaZulu-Natal Province. The benefits appear to be primarily derived from an alien species, Rubus sect. Arguti. Management of the 6 species of invasive Rubus could be optimised by the prioritisation of those regions that incur the highest cost and derive the lowest benefit, in this case KwaZulu-Natal Province. Likewise, those regions with the highest benefits and lowest costs, the Free State Province, could provide sites for increased use and beneficiation of berries from invasive species. Management of individual species may prove difficult, given the similar morphologies, and thus, (i) either specialised training for those engaged in control must be instituted, (ii) all species of alien Rubus should be earmarked for management, or (iii) highly specific biocontrol agents for the most problematic species must be found. , Thesis (MEcon) -- Faculty of Commerce, Economics and Economic History, 2021
- Full Text:
Distribution, ecological and economic impacts and competition of the invasive alien aquatic weeds (Pontederia crassipes Mart., Pistia stratiotes L., Salvinia molesta D.S. Mitch. and Azolla filiculoides Lam.) in Madagascar
- Authors: Lehavana, Adolphe
- Date: 2021-10-29
- Subjects: Pontederiaceae Madagascar , Water lettuce Madagascar , Salvinia molesta Madagascar , Azolla filiculoides Madagascar , Introduced aquatic organisms , Aquatic weeds Economic aspects , Aquatic weeds Social aspects , Aquatic weeds Geographical distribution
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191225 , vital:45072
- Description: In Madagascar, as in several countries in the world, the invasion by four aquatic weeds (Pontederia crassipes Mart. (Pontederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitch Salviniaceae) and Azolla filiculoides Lam. (Azollaceae) are among the drivers of environmental and socio-economic deterioration in aquatic ecosystems. Pistia stratiotes was first recorded on the island in the 19th century, and P. crassipes from the beginning of the 20th century, while S. molesta and A. filiculoides were only documented during in the 21st century. From the 1920s, botanists such as Henri Perrier de la Bathie and Raymond Decary were already aware of the dangers caused, in particular by P. crassipes in other countries, and raised the alarm, but little attention has been paid to these species. The aim of the research conducted for this thesis was to determine the distribution, socio-economic and ecological impacts of these four invasive alien aquatic weeds in Madagascar and to make recommendations for their control. First, the distributions of these four aquatic weeds were mapped. This mapping exercise compiled data from different sources including herbarium records, online data and field visits across Madagascar. The mapping study was undertaken from August 2015 to June 2020. Except for mountainous areas above 1800 m (Tsaratanana Massif, Ankaratra Massif and Andringitra Massif) where no data were available, all of Madagascar's bioclimates were invaded by at least one of the four aquatic weeds. In total, at least one species was recorded in 18 of the 22 Regions. Pontederia crassipes was recorded in 13 Regions, S. molesta in 14 Regions, P. stratiotes in 12 Regions, and A. filiculoides in 13 Regions. Herbarium records revealed the oldest record for P. stratiotes to be 1847, 1931 for P. crassipes, 1995 for S. molesta and there were no herbarium specimens for A. filiculoides prior to the start of the current study in 2015. We now know where these four weeds occur and how abundant they are. An objective of this research was to assess the impacts of the four invasive aquatic plants on the socio-economy of the island, mainly on rice production and fishing. Between 2016 and 2019, 102 households in three regions, Soanierana Ivongo, Foulpointe and Antananarivo, were randomly selected and questioned on the impact of these weeds in their aquatic ecosystems and their livelihoods such as fishing and rice growing. Surveys revealed that the four aquatic weeds significantly threatened household activities. On the east coast of Madagascar, the invasions of these four invasive species decreased fish and freshwater shrimp production by 82%. On the high plateau of Madagascar, they reduced rice yield by 30% despite requiring an additional expense of US$ 1,107/ha for control. Although farmers surveyed only used manual control to manage these weeds, they were receptive to other control methods, including integrated control using herbicides and biological control. Another objective of this research was to determine the ecological impacts of the four weeds and specifically if freshwater ecosystem functioning would return after control. To assess the ecological impact, between February 2017 to August 2019, on Lake Antsokafina, the following abiotic and biotic factors were considered: physico-chemistry of water, succession of macrophyte community and animal diversity. With the exception of turbidity, the values of the physico-chemical parameters of the water (pH, electrical conductivity, water temperature and turbidity), were similar between the infested zone and cleared zone. A study on the invasion process of aquatic weeds showed that the plant community succession of the lake changed over time in the areas that had been cleared. The submerged species Ceratophyllum demersum was the pioneer, followed by creeping species such as Echinochloa colona and Ipomoea aquatica, before the area was recolonized by aquatic weeds. Among the aquatic weeds, S. molesta was the most aggressive, covering 92% of the area one year after the start of the experiment. For animal diversity, bird, shrimp and fish community were assessed. The cleaning of the plots in the lake allowed the resumption of fishing activity providing 50 to 200g/catch for shrimp and from 0.25 to 0.5kg/catch for fish per person per day, while no catch was obtained in the areas infested by aquatic weeds were fishermen still attempting to harvest fish/shrimp from the aquatic weed infested areas. Three species of birds, Humblot’s Heron (Ardea humbloti), the white-faced whistling duck (Dendrocygna viduata) and red-billed teal (Anas erythrorhyncha) returned once the areas had been cleared. A manipulated outdoor as descriptor for laboratory experiment was conducted to determine the level and nature of competition of four aquatic weeds species against the indigenous floating fern, Salvinia hastata Desv. (Salviniaceae), using an additive series density model. It was shown that all four invasive species outcompeted S. hastata, with P. crassipes being 24 times more dominant, followed by P. stratiotes at 12 times, S. molesta at 8 times, and finally A. filiculoides at 1.2 times more dominant. This study provided direct evidence of the biodiversity impact of these four species and thus also provided an environmental argument for their control. Based on the findings of this study, a series of recommendations was formulated to manage the invasions of alien species in Madagascar with particular attention to invasive aquatic weeds. These recommendations mainly concern the establishment of management structures and legal instruments such as the creation of a lead government agency at national level and a cross-sectorial invasive species advisory committee, which should review legislation and regulations related to invasive species. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Authors: Lehavana, Adolphe
- Date: 2021-10-29
- Subjects: Pontederiaceae Madagascar , Water lettuce Madagascar , Salvinia molesta Madagascar , Azolla filiculoides Madagascar , Introduced aquatic organisms , Aquatic weeds Economic aspects , Aquatic weeds Social aspects , Aquatic weeds Geographical distribution
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191225 , vital:45072
- Description: In Madagascar, as in several countries in the world, the invasion by four aquatic weeds (Pontederia crassipes Mart. (Pontederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitch Salviniaceae) and Azolla filiculoides Lam. (Azollaceae) are among the drivers of environmental and socio-economic deterioration in aquatic ecosystems. Pistia stratiotes was first recorded on the island in the 19th century, and P. crassipes from the beginning of the 20th century, while S. molesta and A. filiculoides were only documented during in the 21st century. From the 1920s, botanists such as Henri Perrier de la Bathie and Raymond Decary were already aware of the dangers caused, in particular by P. crassipes in other countries, and raised the alarm, but little attention has been paid to these species. The aim of the research conducted for this thesis was to determine the distribution, socio-economic and ecological impacts of these four invasive alien aquatic weeds in Madagascar and to make recommendations for their control. First, the distributions of these four aquatic weeds were mapped. This mapping exercise compiled data from different sources including herbarium records, online data and field visits across Madagascar. The mapping study was undertaken from August 2015 to June 2020. Except for mountainous areas above 1800 m (Tsaratanana Massif, Ankaratra Massif and Andringitra Massif) where no data were available, all of Madagascar's bioclimates were invaded by at least one of the four aquatic weeds. In total, at least one species was recorded in 18 of the 22 Regions. Pontederia crassipes was recorded in 13 Regions, S. molesta in 14 Regions, P. stratiotes in 12 Regions, and A. filiculoides in 13 Regions. Herbarium records revealed the oldest record for P. stratiotes to be 1847, 1931 for P. crassipes, 1995 for S. molesta and there were no herbarium specimens for A. filiculoides prior to the start of the current study in 2015. We now know where these four weeds occur and how abundant they are. An objective of this research was to assess the impacts of the four invasive aquatic plants on the socio-economy of the island, mainly on rice production and fishing. Between 2016 and 2019, 102 households in three regions, Soanierana Ivongo, Foulpointe and Antananarivo, were randomly selected and questioned on the impact of these weeds in their aquatic ecosystems and their livelihoods such as fishing and rice growing. Surveys revealed that the four aquatic weeds significantly threatened household activities. On the east coast of Madagascar, the invasions of these four invasive species decreased fish and freshwater shrimp production by 82%. On the high plateau of Madagascar, they reduced rice yield by 30% despite requiring an additional expense of US$ 1,107/ha for control. Although farmers surveyed only used manual control to manage these weeds, they were receptive to other control methods, including integrated control using herbicides and biological control. Another objective of this research was to determine the ecological impacts of the four weeds and specifically if freshwater ecosystem functioning would return after control. To assess the ecological impact, between February 2017 to August 2019, on Lake Antsokafina, the following abiotic and biotic factors were considered: physico-chemistry of water, succession of macrophyte community and animal diversity. With the exception of turbidity, the values of the physico-chemical parameters of the water (pH, electrical conductivity, water temperature and turbidity), were similar between the infested zone and cleared zone. A study on the invasion process of aquatic weeds showed that the plant community succession of the lake changed over time in the areas that had been cleared. The submerged species Ceratophyllum demersum was the pioneer, followed by creeping species such as Echinochloa colona and Ipomoea aquatica, before the area was recolonized by aquatic weeds. Among the aquatic weeds, S. molesta was the most aggressive, covering 92% of the area one year after the start of the experiment. For animal diversity, bird, shrimp and fish community were assessed. The cleaning of the plots in the lake allowed the resumption of fishing activity providing 50 to 200g/catch for shrimp and from 0.25 to 0.5kg/catch for fish per person per day, while no catch was obtained in the areas infested by aquatic weeds were fishermen still attempting to harvest fish/shrimp from the aquatic weed infested areas. Three species of birds, Humblot’s Heron (Ardea humbloti), the white-faced whistling duck (Dendrocygna viduata) and red-billed teal (Anas erythrorhyncha) returned once the areas had been cleared. A manipulated outdoor as descriptor for laboratory experiment was conducted to determine the level and nature of competition of four aquatic weeds species against the indigenous floating fern, Salvinia hastata Desv. (Salviniaceae), using an additive series density model. It was shown that all four invasive species outcompeted S. hastata, with P. crassipes being 24 times more dominant, followed by P. stratiotes at 12 times, S. molesta at 8 times, and finally A. filiculoides at 1.2 times more dominant. This study provided direct evidence of the biodiversity impact of these four species and thus also provided an environmental argument for their control. Based on the findings of this study, a series of recommendations was formulated to manage the invasions of alien species in Madagascar with particular attention to invasive aquatic weeds. These recommendations mainly concern the establishment of management structures and legal instruments such as the creation of a lead government agency at national level and a cross-sectorial invasive species advisory committee, which should review legislation and regulations related to invasive species. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
Aspects of the biology, thermal physiology and nutritional ecology of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), a specialist herbivore introduced into South Africa for the biological control of Chromolaena odorata (L.) King and Robinson (Asteraceae)
- Authors: Uyi, Osariyekemwen
- Date: 2015
- Subjects: Chromolaena odorata , Chromolaena odorata -- Biological control -- South Africa , Arctiidae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5936 , http://hdl.handle.net/10962/d1017916
- Description: Chromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub native to the Americas that has proven to be a significant economic and ecological burden to many tropical and sub-tropical regions of the world where it impacts negatively on agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against the weed between 2001 and 2009. Although the moth did establish at one out of some 30 release sites, its population level is generally low in the field. This thesis attempts to unravel the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess good biological attributes such as low mortality, high fecundity, egg hatchability and high female mating success. Overall, adult female moths eclosed before their male counterparts suggesting the presence of protogyny. Beyond the contribution of this study to our understanding of the life history traits of erebid moths, it hypothesized that the absence of protandry might have contributed to the low population levels of the moth in the field. To determine if a degree of agent-host plant incompatibility is culpable for the poor performance of P. insulata, insect performance metrics were compared on two distinct C. odorata plants (one from Florida and another from South Africa) in laboratory experiments. Pareuchaetes insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and fecundity between the Floridian and southern African C. odorata plants. In sum, there was no evidence to demonstrate that differences in plant forms in C. odorata are culpable for the poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits, locomotion performance and thermal tolerance range of P. insulata were studied in order to elucidate the possible role of temperature on the poor performance of the moth. The results showed that at temperatures below 25 °C, mortality increased and development time was prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6 °C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized that both direct and indirect negative impacts of low temperature may partly explain the poor performance of P. insulata in South Africa. Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn (relative to winter) were more nutritionally balanced and suitable for herbivore performance. Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity when reared on shaded leaves (relative to full sun) or when reared on autumn leaves compared to leaves growing in winter. This study demonstrates that low winter temperatures can indirectly affect insect herbivore performance by changing the phytochemistry of host plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality, prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated with the performance of P. insulata. From this study, it is demonstrably evident that the poor performance of P. insulata on C. odorata in South Africa is caused by multiple factors such as low temperatures as well as spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows the complexity of determining the causes of low populations and apparent low impact of biological control agents and herbivorous insects generally, in the field. The implications of this research to the biological control programme against C. odorata and the direction of future research for the control of C. odorata are discussed.
- Full Text:
- Authors: Uyi, Osariyekemwen
- Date: 2015
- Subjects: Chromolaena odorata , Chromolaena odorata -- Biological control -- South Africa , Arctiidae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5936 , http://hdl.handle.net/10962/d1017916
- Description: Chromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub native to the Americas that has proven to be a significant economic and ecological burden to many tropical and sub-tropical regions of the world where it impacts negatively on agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against the weed between 2001 and 2009. Although the moth did establish at one out of some 30 release sites, its population level is generally low in the field. This thesis attempts to unravel the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess good biological attributes such as low mortality, high fecundity, egg hatchability and high female mating success. Overall, adult female moths eclosed before their male counterparts suggesting the presence of protogyny. Beyond the contribution of this study to our understanding of the life history traits of erebid moths, it hypothesized that the absence of protandry might have contributed to the low population levels of the moth in the field. To determine if a degree of agent-host plant incompatibility is culpable for the poor performance of P. insulata, insect performance metrics were compared on two distinct C. odorata plants (one from Florida and another from South Africa) in laboratory experiments. Pareuchaetes insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and fecundity between the Floridian and southern African C. odorata plants. In sum, there was no evidence to demonstrate that differences in plant forms in C. odorata are culpable for the poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits, locomotion performance and thermal tolerance range of P. insulata were studied in order to elucidate the possible role of temperature on the poor performance of the moth. The results showed that at temperatures below 25 °C, mortality increased and development time was prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6 °C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized that both direct and indirect negative impacts of low temperature may partly explain the poor performance of P. insulata in South Africa. Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn (relative to winter) were more nutritionally balanced and suitable for herbivore performance. Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity when reared on shaded leaves (relative to full sun) or when reared on autumn leaves compared to leaves growing in winter. This study demonstrates that low winter temperatures can indirectly affect insect herbivore performance by changing the phytochemistry of host plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality, prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated with the performance of P. insulata. From this study, it is demonstrably evident that the poor performance of P. insulata on C. odorata in South Africa is caused by multiple factors such as low temperatures as well as spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows the complexity of determining the causes of low populations and apparent low impact of biological control agents and herbivorous insects generally, in the field. The implications of this research to the biological control programme against C. odorata and the direction of future research for the control of C. odorata are discussed.
- Full Text:
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