Developing an attractant for monitoring fruit-feeding moths in citrus orchards
- Authors: Goddard, Mathew Keith
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2981 , vital:20349
- Description: Fruit-piercing moths are a sporadic pest of citrus, especially in the Eastern Cape Province of South Africa, where the adults can cause significant damage in outbreak years. Currently the only way in which to successfully control fruit-feeding moths within the orchards is the use of repellent lights. However, growers confuse fruit-piercing moths with fruit-sucking moths that don‘t cause primary damage, and there is no way of monitoring which moth species are attacking the fruit in the orchards during the night. In a previous study, banana was shown to be the most attractive bait for a variety of fruit-feeding moth species. Therefore the aim of this study was to determine the population dynamics of fruit-feeding moths develop a cost-effective alternative to the use of fresh banana as a bait for fruit-piercing moths. Fresh banana was compared to nine alternative synthetic attractants, frozen banana and a control under field conditions in several orchards in the Eastern Cape Province. Once again, banana was shown to be the most attractive bait. Some 23 species of fruit-feeding moth species were sampled in the traps, but there was only two fruit-piercing species, Serrodes partita (Fabricius) (Lepidoptera: Noctuidae) and Eudocima sp. Surprisingly S. partita, which was thought to be the main pest, comprised only 6.9% of trap catches. Serrodes partita, is a sporadic pest, only becoming problematic every five to 10 years after good rainfall in the Little Karoo region that causes flushes of their larval host, wild plum, Pappea capensis (Ecklon and Zeyher). During these outbreaks, damage to fruit can range from 70 to 90% and this is especially so for soft skinned citrus. A study on the morphology of the proboscis confirmed that only two species of fruit-piercing moths were present. Trap catches over three citrus growing seasons was linked to fruit damage found within several orchards. Once again fruit-piercing moth damage was relatively low in comparison to other types of damage such as mechanical and undefined damage. There was a very weak correlation between S. partita trap catches and damage, but generally damage was recorded two to three weeks after a peak in S. partita trap catches. Climatic conditions were also recorded and compared to weekly trap catches of S. partita, and while temperature and wind direction had no influence on moth populations, precipitation in the orchards was weakly correlated with trap catches. This study has shown that in non-outbreak seasons, the main fruit-piercing moth, S. partita comprises a small percentage of fruit-feeding moths in citrus orchards, but that growers are unable to determine the difference between fruit-piercing species and the harmless fruit-sucking species. Further fresh banana remains the best method for attracting fruit-piecing moths to traps, but this is not cost effective and thus a commercially viable protocol for monitoring these species remains elusive.
- Full Text:
- Authors: Goddard, Mathew Keith
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/2981 , vital:20349
- Description: Fruit-piercing moths are a sporadic pest of citrus, especially in the Eastern Cape Province of South Africa, where the adults can cause significant damage in outbreak years. Currently the only way in which to successfully control fruit-feeding moths within the orchards is the use of repellent lights. However, growers confuse fruit-piercing moths with fruit-sucking moths that don‘t cause primary damage, and there is no way of monitoring which moth species are attacking the fruit in the orchards during the night. In a previous study, banana was shown to be the most attractive bait for a variety of fruit-feeding moth species. Therefore the aim of this study was to determine the population dynamics of fruit-feeding moths develop a cost-effective alternative to the use of fresh banana as a bait for fruit-piercing moths. Fresh banana was compared to nine alternative synthetic attractants, frozen banana and a control under field conditions in several orchards in the Eastern Cape Province. Once again, banana was shown to be the most attractive bait. Some 23 species of fruit-feeding moth species were sampled in the traps, but there was only two fruit-piercing species, Serrodes partita (Fabricius) (Lepidoptera: Noctuidae) and Eudocima sp. Surprisingly S. partita, which was thought to be the main pest, comprised only 6.9% of trap catches. Serrodes partita, is a sporadic pest, only becoming problematic every five to 10 years after good rainfall in the Little Karoo region that causes flushes of their larval host, wild plum, Pappea capensis (Ecklon and Zeyher). During these outbreaks, damage to fruit can range from 70 to 90% and this is especially so for soft skinned citrus. A study on the morphology of the proboscis confirmed that only two species of fruit-piercing moths were present. Trap catches over three citrus growing seasons was linked to fruit damage found within several orchards. Once again fruit-piercing moth damage was relatively low in comparison to other types of damage such as mechanical and undefined damage. There was a very weak correlation between S. partita trap catches and damage, but generally damage was recorded two to three weeks after a peak in S. partita trap catches. Climatic conditions were also recorded and compared to weekly trap catches of S. partita, and while temperature and wind direction had no influence on moth populations, precipitation in the orchards was weakly correlated with trap catches. This study has shown that in non-outbreak seasons, the main fruit-piercing moth, S. partita comprises a small percentage of fruit-feeding moths in citrus orchards, but that growers are unable to determine the difference between fruit-piercing species and the harmless fruit-sucking species. Further fresh banana remains the best method for attracting fruit-piecing moths to traps, but this is not cost effective and thus a commercially viable protocol for monitoring these species remains elusive.
- Full Text:
Effects of the biocontrol agent, coelocephalapion camarae kissinger, galling on petiole tissues, plant growth and stored reserves in plant parts of two lantana camara L.(verbenaceae) varieties
- Authors: Kistensamy, Yoganambal
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3126 , vital:20372
- Description: The agent evaluated in this study, Coelocephalapion camarae Kissinger (Brentidae), a petiole galling apionid, was released against Lantana camara L. (Verbenaceae) in South Africa and has the potential to significantly contribute to the control of this noxious weed. An important aspect of evaluating the effectiveness of a biocontrol agent; include the understanding of the mechanism in which the biocontrol agent causes damage to the plant and the plant’s response to this damage. Another aspect that was considered in evaluating the effects of the apionid was the varietal differences that exist within the weedy L. camara complex. Larval feeding of C. camarae damaged the tissue in the petioles causing gall formation and this was quantified on two common South African L. camara varieties (017 and 018). Up to 100% of the vascular tissue (xylem and phloem) of effected petioles was eaten by larvae, 25 days after ovipostion in both the L. camara varieties, effectively severing the vascular connection from the leaves. The effect of feeding and galling by different population densities of C. camarae, on biomass and total soluble sugar and starch concentrations of different plant parts was measured on these two varieties during autumn, and compared to a similar study, done during summer. Relatively low galling percentages were achieved in the experiments of this study. Plant growth was less affected by apionid feeding at similar galling levels, as higher galling densities in these trials were similar to those at low exposures in trials by Baars (2002). The dry weights of all individual and combined plant parts for lantana variety 017 was less for both adult density exposures after 70 days compared to the weights of its controls, although not statistically significant at P>0.05 The opposite effect, though barely noticeable was recorded for lantana variety 018; here, the dry weights of individual plant parts and as whole plants weighed more in the plants exposed to both densities of weevil feeding and galling after 70 days, compared to its controls. Coelocephalapion camarae herbivory may thus be more effective in inflicting damage on some L. camara varieties compared to others. The effects of late season carbohydrate storage revealed that, from early- to mid-autumn starch concentrations increased significantly in stems of both L. camara varieties and L. camara var. 018 had larger starch reserves for winter. In L. camara var. 018 stems, starch increased 52 times and concentrations doubled in stems of L. camara var 017. The increase in the sugar and decrease in starch concentrations in leaves of plants of both varieties exposed to apionids in this study was attributed to a possible reduction of available nitrogen and phosphorus, due to apionid feeding, whilst starch was reallocated within the plants to stems and roots. The increase in starch concentrations in stems of plants that were exposed to apionids may have been expected, as compensation for herbivory has been associated with, increases in photosynthetic rates and the mobilization of stored resources. Herbivory by the apionid early in the growing season may be easily compensated for by L. camara as there are nutrient flushes experienced by plants that allows the maximum uptake of nutrients facilitating recovery, whereas later in the season plants suffer lower nutrient availability and don’t recover so readily. Both early and late in the season the accumulated effects of C. camarae feeding over time will undoubtedly decrease fitness of most lantana varieties.
- Full Text:
- Authors: Kistensamy, Yoganambal
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3126 , vital:20372
- Description: The agent evaluated in this study, Coelocephalapion camarae Kissinger (Brentidae), a petiole galling apionid, was released against Lantana camara L. (Verbenaceae) in South Africa and has the potential to significantly contribute to the control of this noxious weed. An important aspect of evaluating the effectiveness of a biocontrol agent; include the understanding of the mechanism in which the biocontrol agent causes damage to the plant and the plant’s response to this damage. Another aspect that was considered in evaluating the effects of the apionid was the varietal differences that exist within the weedy L. camara complex. Larval feeding of C. camarae damaged the tissue in the petioles causing gall formation and this was quantified on two common South African L. camara varieties (017 and 018). Up to 100% of the vascular tissue (xylem and phloem) of effected petioles was eaten by larvae, 25 days after ovipostion in both the L. camara varieties, effectively severing the vascular connection from the leaves. The effect of feeding and galling by different population densities of C. camarae, on biomass and total soluble sugar and starch concentrations of different plant parts was measured on these two varieties during autumn, and compared to a similar study, done during summer. Relatively low galling percentages were achieved in the experiments of this study. Plant growth was less affected by apionid feeding at similar galling levels, as higher galling densities in these trials were similar to those at low exposures in trials by Baars (2002). The dry weights of all individual and combined plant parts for lantana variety 017 was less for both adult density exposures after 70 days compared to the weights of its controls, although not statistically significant at P>0.05 The opposite effect, though barely noticeable was recorded for lantana variety 018; here, the dry weights of individual plant parts and as whole plants weighed more in the plants exposed to both densities of weevil feeding and galling after 70 days, compared to its controls. Coelocephalapion camarae herbivory may thus be more effective in inflicting damage on some L. camara varieties compared to others. The effects of late season carbohydrate storage revealed that, from early- to mid-autumn starch concentrations increased significantly in stems of both L. camara varieties and L. camara var. 018 had larger starch reserves for winter. In L. camara var. 018 stems, starch increased 52 times and concentrations doubled in stems of L. camara var 017. The increase in the sugar and decrease in starch concentrations in leaves of plants of both varieties exposed to apionids in this study was attributed to a possible reduction of available nitrogen and phosphorus, due to apionid feeding, whilst starch was reallocated within the plants to stems and roots. The increase in starch concentrations in stems of plants that were exposed to apionids may have been expected, as compensation for herbivory has been associated with, increases in photosynthetic rates and the mobilization of stored resources. Herbivory by the apionid early in the growing season may be easily compensated for by L. camara as there are nutrient flushes experienced by plants that allows the maximum uptake of nutrients facilitating recovery, whereas later in the season plants suffer lower nutrient availability and don’t recover so readily. Both early and late in the season the accumulated effects of C. camarae feeding over time will undoubtedly decrease fitness of most lantana varieties.
- Full Text:
Field evaluation of the use of select entomopathogenic fungal isolates as microbial control agents of the soil-dwelling life stages of a key South African citrus pest, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae)
- Authors: Coombes, Candice Anne
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/507 , vital:19965
- Description: The control of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick, 1912) (Lepidoptera: Tortricidae), in citrus orchards is strongly reliant on the use of integrated pest management as key export markets impose stringent chemical restrictions on exported fruit and have a strict no entry policy towards this phytosanitary pest. Most current, registered control methods target the above-ground life stages of FCM, not the soil-dwelling life stages. As such, entomopathogenic fungi which are ubiquitous, percutaneously infective soil-borne microbes that have been used successfully as control agents worldwide, present ideal candidates as additional control agents. Following an initial identification of 62 fungal entomopathogens isolated from soil collected from citrus orchards in the Eastern Cape Province, South Africa, further laboratory research has highlighted three isolates as having the greatest control potential against FCM subterranean life stages: Metarhizium anisopliae G 11 3 L6 (Ma1), M. anisopliae FCM Ar 23 B3 (Ma2) and Beauveria bassiana G Ar 17 B3 (Bb1). These isolates are capable of causing above 80% laboratory-induced mycosis of FCM fifth instars. Whether this level of efficacy was obtainable under sub-optimal and fluctuating field conditions was unknown. Thus, this thesis aimed to address the following issues with regards to the three most laboratory-virulent fungal isolates: field efficacy, field persistence, optimal application rate, application timing, environmental dependency, compatibility with fungicides and the use of different wetting agents to promote field efficacy. Following fungal application to one hectare treatment blocks in the field, FCM infestation within fruit was reduced by 28.3% to 81.7%. Isolate Bb1 performed best under moderate to high soil moisture whilst Ma2 was more effective under low soil moisture conditions. All isolates, with the exception of Ma2 at one site, were recorded in the soil five months post-application. None of the wetting agents tested were found to be highly toxic to fungal germination and similar physical suspension characteristics were observed. Fungicide toxicity varied amongst isolates and test conditions. However, only Dithane (a.i. mancozeb) was considered incompatible with isolate Ma2. The implication of these results and the way forward is discussed. This study is the first report of the field efficacy of three laboratory-virulent fungal isolates applied to the soil of conventional citrus orchards against FCM soil-dwelling life stages. As such, it provides a foundation on which future research can build to ensure the development and commercialisation of a cost-effective and consistently reliable product.
- Full Text:
- Authors: Coombes, Candice Anne
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/507 , vital:19965
- Description: The control of false codling moth (FCM), Thaumatotibia leucotreta (Meyrick, 1912) (Lepidoptera: Tortricidae), in citrus orchards is strongly reliant on the use of integrated pest management as key export markets impose stringent chemical restrictions on exported fruit and have a strict no entry policy towards this phytosanitary pest. Most current, registered control methods target the above-ground life stages of FCM, not the soil-dwelling life stages. As such, entomopathogenic fungi which are ubiquitous, percutaneously infective soil-borne microbes that have been used successfully as control agents worldwide, present ideal candidates as additional control agents. Following an initial identification of 62 fungal entomopathogens isolated from soil collected from citrus orchards in the Eastern Cape Province, South Africa, further laboratory research has highlighted three isolates as having the greatest control potential against FCM subterranean life stages: Metarhizium anisopliae G 11 3 L6 (Ma1), M. anisopliae FCM Ar 23 B3 (Ma2) and Beauveria bassiana G Ar 17 B3 (Bb1). These isolates are capable of causing above 80% laboratory-induced mycosis of FCM fifth instars. Whether this level of efficacy was obtainable under sub-optimal and fluctuating field conditions was unknown. Thus, this thesis aimed to address the following issues with regards to the three most laboratory-virulent fungal isolates: field efficacy, field persistence, optimal application rate, application timing, environmental dependency, compatibility with fungicides and the use of different wetting agents to promote field efficacy. Following fungal application to one hectare treatment blocks in the field, FCM infestation within fruit was reduced by 28.3% to 81.7%. Isolate Bb1 performed best under moderate to high soil moisture whilst Ma2 was more effective under low soil moisture conditions. All isolates, with the exception of Ma2 at one site, were recorded in the soil five months post-application. None of the wetting agents tested were found to be highly toxic to fungal germination and similar physical suspension characteristics were observed. Fungicide toxicity varied amongst isolates and test conditions. However, only Dithane (a.i. mancozeb) was considered incompatible with isolate Ma2. The implication of these results and the way forward is discussed. This study is the first report of the field efficacy of three laboratory-virulent fungal isolates applied to the soil of conventional citrus orchards against FCM soil-dwelling life stages. As such, it provides a foundation on which future research can build to ensure the development and commercialisation of a cost-effective and consistently reliable product.
- Full Text:
Genetic and biological characterisation of a novel South African Cydia pomonella granulovirus (CpGV-SA) isolate
- Motsoeneng, Boitumelo Madika
- Authors: Motsoeneng, Boitumelo Madika
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:20503 , http://hdl.handle.net/10962/d1021266
- Description: The codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is the primary pest of pome fruit cultivated worldwide. The control of this insect pest has been dependent on the frequent use of broad-spectrum chemical pesticides, which has led to the development of resistance in pest populations and negative effects on human health and the environment. The Betabaculovirus of C. pomonella has successfully been applied as a biological control agent in integrated pest management (IPM) programmes for the suppression of pest populations worldwide. Previously, all Cydia pomonella granulovirus (CpGV) biopesticides were based on a Mexican isolate (CpGV-M) and although these products are highly efficient at controlling C. pomonella, resistance cases have been reported across Europe. The identification of novel CpGV isolates as additional or alternative control agents to manage resistance is therefore necessary. This study aimed to genetically and biologically characterise a novel South African C. pomonella granulovirus isolate and to test its virulence against neonate larvae. Based on the morphology of the occlusion bodies observed using transmission electron microscopy, granuloviruses were recovered from diseased and dead larvae collected from an orchard in South Africa where no virus applications had been made. DNA was extracted and the identification of the isolated granulovirus was achieved through the PCR amplification and sequencing of the lef-8, lef-9, granulin and egt genes. Submission of the gene sequences to BLAST revealed high percentage identities to sequences from various CpGV isolates, resulting in the naming of the isolate in this study as the South African Cydia pomonella granulovirus (CpGV-SA) isolate. Phylogenetic analysis based on the single nucleotide polymorphisms (SNPs) detected in the lef-8, lef-9 and granulin nucleotide sequences grouped the South African isolate with CpGV-E2 (genome type B) and CpGV-S (genome type E). The CpGV-SA isolate was further genetically characterised by restriction endonuclease analysis and complete sequencing of the genomic DNA. Differences were observed for the BamHI, EcoRI, PstI and XhoI profiles of CpGV-SA in comparison to the respective profiles generated for CpGV-M extracted from a biopesticide, Carpovirusine® (Arysta Lifescience, France). Several genetic variations between the complete genome sequence of CpGV-SA and the reference isolate, CpGV-M1, as well as a recent genome submission of CpGV-M, both representing genome type A were observed. The complete genome analysis confirmed that CpGV-SA is genetically different from the Mexican CpGV isolate, used in thedevelopment of most biopesticides. In silico restriction profiles of the genome sequence obtained for CpGV-SA and genome sequences of genetically different CpGV isolates originating from Mexico (M1 and M), England (E2), Canada (S) and Iran (I12 and I07), available on the NCBI’s GenBank database confirmed that CpGV-SA is of mixed genotypes. Furthermore, the South African isolate shared the single common difference found in the pe38 gene of resistance overcoming isolates, which was the absence of an internal 24 nucleotide repeat present in CpGV-M1. In addition to the common difference, SNPs detected in the pe38 gene grouped the isolate with the CpGV-S isolate, suggesting that the CpGV-SA isolate is predominantly of genome type E. To determine the biological activity of CpGV-SA against neonate C. pomonella larvae, surface bioassays were conducted alongside CpGV-M (Carpovirusine®) bioassays. The LC50 and LC90 values for the South African isolate were 1.6 × 103 and 1.2 × 105 OBs/ml respectively. The LT50 was determined to be 135 hours. These values were similar to the values obtained for CpGV-M (Carpovirusine®). The results in this study suggest that a novel South African CpGV isolate of mixed genotypes, potentially able to overcome resistance in C. pomonella, with biological activity similar to CpGV-M (Carpovirusine®) and important for the control of C. pomonella was recovered. The CpGV-SA isolate could therefore potentially be developed into a biopesticide for use in resistance management strategies against C. pomonella populations in South Africa.
- Full Text:
- Authors: Motsoeneng, Boitumelo Madika
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:20503 , http://hdl.handle.net/10962/d1021266
- Description: The codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), is the primary pest of pome fruit cultivated worldwide. The control of this insect pest has been dependent on the frequent use of broad-spectrum chemical pesticides, which has led to the development of resistance in pest populations and negative effects on human health and the environment. The Betabaculovirus of C. pomonella has successfully been applied as a biological control agent in integrated pest management (IPM) programmes for the suppression of pest populations worldwide. Previously, all Cydia pomonella granulovirus (CpGV) biopesticides were based on a Mexican isolate (CpGV-M) and although these products are highly efficient at controlling C. pomonella, resistance cases have been reported across Europe. The identification of novel CpGV isolates as additional or alternative control agents to manage resistance is therefore necessary. This study aimed to genetically and biologically characterise a novel South African C. pomonella granulovirus isolate and to test its virulence against neonate larvae. Based on the morphology of the occlusion bodies observed using transmission electron microscopy, granuloviruses were recovered from diseased and dead larvae collected from an orchard in South Africa where no virus applications had been made. DNA was extracted and the identification of the isolated granulovirus was achieved through the PCR amplification and sequencing of the lef-8, lef-9, granulin and egt genes. Submission of the gene sequences to BLAST revealed high percentage identities to sequences from various CpGV isolates, resulting in the naming of the isolate in this study as the South African Cydia pomonella granulovirus (CpGV-SA) isolate. Phylogenetic analysis based on the single nucleotide polymorphisms (SNPs) detected in the lef-8, lef-9 and granulin nucleotide sequences grouped the South African isolate with CpGV-E2 (genome type B) and CpGV-S (genome type E). The CpGV-SA isolate was further genetically characterised by restriction endonuclease analysis and complete sequencing of the genomic DNA. Differences were observed for the BamHI, EcoRI, PstI and XhoI profiles of CpGV-SA in comparison to the respective profiles generated for CpGV-M extracted from a biopesticide, Carpovirusine® (Arysta Lifescience, France). Several genetic variations between the complete genome sequence of CpGV-SA and the reference isolate, CpGV-M1, as well as a recent genome submission of CpGV-M, both representing genome type A were observed. The complete genome analysis confirmed that CpGV-SA is genetically different from the Mexican CpGV isolate, used in thedevelopment of most biopesticides. In silico restriction profiles of the genome sequence obtained for CpGV-SA and genome sequences of genetically different CpGV isolates originating from Mexico (M1 and M), England (E2), Canada (S) and Iran (I12 and I07), available on the NCBI’s GenBank database confirmed that CpGV-SA is of mixed genotypes. Furthermore, the South African isolate shared the single common difference found in the pe38 gene of resistance overcoming isolates, which was the absence of an internal 24 nucleotide repeat present in CpGV-M1. In addition to the common difference, SNPs detected in the pe38 gene grouped the isolate with the CpGV-S isolate, suggesting that the CpGV-SA isolate is predominantly of genome type E. To determine the biological activity of CpGV-SA against neonate C. pomonella larvae, surface bioassays were conducted alongside CpGV-M (Carpovirusine®) bioassays. The LC50 and LC90 values for the South African isolate were 1.6 × 103 and 1.2 × 105 OBs/ml respectively. The LT50 was determined to be 135 hours. These values were similar to the values obtained for CpGV-M (Carpovirusine®). The results in this study suggest that a novel South African CpGV isolate of mixed genotypes, potentially able to overcome resistance in C. pomonella, with biological activity similar to CpGV-M (Carpovirusine®) and important for the control of C. pomonella was recovered. The CpGV-SA isolate could therefore potentially be developed into a biopesticide for use in resistance management strategies against C. pomonella populations in South Africa.
- Full Text:
Life history of the maritime platygastrid Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae: Scelioninae)
- Authors: Owen, Candice Ann
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/837 , vital:19995 , 10.21504/10962/837
- Description: Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae, Scelioninae) is an intertidal parasitoid wasp that uses the eggs of the maritime spider, Desis formidabilis O.P. Cambridge 1890 (Araneae: Desidae), as a host. This species is one of only three known maritime parasitoids globally, and is the only known spider egg parasitoid that attacks its host within the intertidal region in southern Africa. Originally described from ‘The Island’, Kommetjie (Western Cape, South Africa), this shore was the only known locality of the species at the commencement of this thesis. Furthermore, the extent of the parasitism pressure the wasp exerts on D. formidabilis was largely unknown, along with its basic biology (drivers of its broad-scale and fine-scale distribution patterns; parasitism incidence; and sex ratios) and morphological and physiological adaptations for living within the frequently saltwater-inundated environment. This thesis unravelled these aspects, as well as experimentally provided data for many components of the life history of E. lamorali that had only been hypothesized by other authors, at a variety of scales, from the country-wide ecosystem, to single shores, and finally to the scale of the individual. While the distribution of E. lamorali was found to be much wider than previously thought, it remained restricted to the shores of the Cape Peninsula (Western Cape, South Africa). The host spiders were located throughout a much wider distributional range than the wasp, from East London in the east to the Peninsula, but some behavioural and morphological differences were found between those within and outside of the range of the parasitoid, suggesting range-limitation imposed by the host on E. lamorali. This limitation may be strengthened by the general lack of suitable shore types within the close vicinity of the Peninsula. Modelling using macro-climatic conditions suggested that maximum temperatures and humidities were also largely limiting to E. lamorali, although these patterns were not observable in the micro-climates in which the species survives. The wasp populations and spiders within the range of E. lamorali as identified in Chapter 2 were assessed to determine any preferences for local conditions, including location along the Peninsula, nesting sites and intertidal zones within single shores, using AICc modelling, which detected parasitism patterns in D. formidabilis and E. lamorali populations, as well as the sex ratios in the latter species. The models showed that the spider population size and distribution was more influenced by bottom-up factors such as abiotic components of the shore than by parasitism, which only showed density dependence with the host at certain scales. Both host and parasitoid populations illustrated a preference for the middle zone on single shores. Observed spider nest characteristics suggested opportunistic nesting behaviour in the species, although preference was shown for construction along an east-west orientation and in locations with low sun exposure. Along with larger population sizes on the west coast over the east coast (not reflected by E. lamorali), these observations suggest that D. formidabilis prefers cooler environments. Spider brood success was 50% in unparasitized egg-sacs, but this figure halved when E. lamorali gained access to the eggs (of which 100% within a single compartment were parasitized each time). Encapsulation of the embryo was found to be positively correlated with parasitism, indicating some form of host resistance. Resultant parasitoid broods illustrated a strong female bias in the species, as is common for this group of insects. The life history of E. lamorali was then assessed at a smaller scale, that of the individual. Scanning electron microscopy of whole E. lamorali specimens and light microscopy of sectioned specimens demonstrated no morphological adaptations in the trachea and spiracles to cope with saltwater inundation. On the other hand, respirometry experiments categorically demonstrated that the species copes with inundation through the formation of a physical gill over the full habitus, and the induction of a state of torpor to reduce metabolic needs, when submerged. This precludes the need for any further morphological adaptations. Determination of the wasp’s critical thermal tolerance illustrated a wide temperature range with a particularly cold lower limit of -1.1ºC ± 0.16, suggesting the presence of related genera or ancestors in much colder environments. With a much broader distribution than previously thought, and the inclusion of the distributional range of E. lamorali within the Table Mountain National Park, this species is being effectively conserved and managed through the umbrella-conservation of the park. Links to the host proved to vary at differing scales, proving the need for scale considerations to be included in other similar biological and ecological studies. Finally, the species showed physiological adaptation to its intertidal existence. Echthrodesis lamorali, the only discovered maritime spider egg parasitoid in Southern Africa, displayed unusual characteristics at every scale of its life history and as such, warrants further investigation.
- Full Text:
- Authors: Owen, Candice Ann
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/837 , vital:19995 , 10.21504/10962/837
- Description: Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae, Scelioninae) is an intertidal parasitoid wasp that uses the eggs of the maritime spider, Desis formidabilis O.P. Cambridge 1890 (Araneae: Desidae), as a host. This species is one of only three known maritime parasitoids globally, and is the only known spider egg parasitoid that attacks its host within the intertidal region in southern Africa. Originally described from ‘The Island’, Kommetjie (Western Cape, South Africa), this shore was the only known locality of the species at the commencement of this thesis. Furthermore, the extent of the parasitism pressure the wasp exerts on D. formidabilis was largely unknown, along with its basic biology (drivers of its broad-scale and fine-scale distribution patterns; parasitism incidence; and sex ratios) and morphological and physiological adaptations for living within the frequently saltwater-inundated environment. This thesis unravelled these aspects, as well as experimentally provided data for many components of the life history of E. lamorali that had only been hypothesized by other authors, at a variety of scales, from the country-wide ecosystem, to single shores, and finally to the scale of the individual. While the distribution of E. lamorali was found to be much wider than previously thought, it remained restricted to the shores of the Cape Peninsula (Western Cape, South Africa). The host spiders were located throughout a much wider distributional range than the wasp, from East London in the east to the Peninsula, but some behavioural and morphological differences were found between those within and outside of the range of the parasitoid, suggesting range-limitation imposed by the host on E. lamorali. This limitation may be strengthened by the general lack of suitable shore types within the close vicinity of the Peninsula. Modelling using macro-climatic conditions suggested that maximum temperatures and humidities were also largely limiting to E. lamorali, although these patterns were not observable in the micro-climates in which the species survives. The wasp populations and spiders within the range of E. lamorali as identified in Chapter 2 were assessed to determine any preferences for local conditions, including location along the Peninsula, nesting sites and intertidal zones within single shores, using AICc modelling, which detected parasitism patterns in D. formidabilis and E. lamorali populations, as well as the sex ratios in the latter species. The models showed that the spider population size and distribution was more influenced by bottom-up factors such as abiotic components of the shore than by parasitism, which only showed density dependence with the host at certain scales. Both host and parasitoid populations illustrated a preference for the middle zone on single shores. Observed spider nest characteristics suggested opportunistic nesting behaviour in the species, although preference was shown for construction along an east-west orientation and in locations with low sun exposure. Along with larger population sizes on the west coast over the east coast (not reflected by E. lamorali), these observations suggest that D. formidabilis prefers cooler environments. Spider brood success was 50% in unparasitized egg-sacs, but this figure halved when E. lamorali gained access to the eggs (of which 100% within a single compartment were parasitized each time). Encapsulation of the embryo was found to be positively correlated with parasitism, indicating some form of host resistance. Resultant parasitoid broods illustrated a strong female bias in the species, as is common for this group of insects. The life history of E. lamorali was then assessed at a smaller scale, that of the individual. Scanning electron microscopy of whole E. lamorali specimens and light microscopy of sectioned specimens demonstrated no morphological adaptations in the trachea and spiracles to cope with saltwater inundation. On the other hand, respirometry experiments categorically demonstrated that the species copes with inundation through the formation of a physical gill over the full habitus, and the induction of a state of torpor to reduce metabolic needs, when submerged. This precludes the need for any further morphological adaptations. Determination of the wasp’s critical thermal tolerance illustrated a wide temperature range with a particularly cold lower limit of -1.1ºC ± 0.16, suggesting the presence of related genera or ancestors in much colder environments. With a much broader distribution than previously thought, and the inclusion of the distributional range of E. lamorali within the Table Mountain National Park, this species is being effectively conserved and managed through the umbrella-conservation of the park. Links to the host proved to vary at differing scales, proving the need for scale considerations to be included in other similar biological and ecological studies. Finally, the species showed physiological adaptation to its intertidal existence. Echthrodesis lamorali, the only discovered maritime spider egg parasitoid in Southern Africa, displayed unusual characteristics at every scale of its life history and as such, warrants further investigation.
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Mapping Nitrogen Loading in Freshwater Systems: Using Aquatic Biota to Trace Nutrients
- Authors: Motitsoe, Samuel Nkopane
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5945 , http://hdl.handle.net/10962/d1020819
- Description: The majority of river systems in developing countries like South Africa, are found in catchments areas that are densely human populated, therefore are subjected to intense land-use and developmental pressures. Anthropogenic nutrient pollution or the excessive addition of nutrients is one important type of stressors that river systems often experience through intense land-use, which includes poor waste management and agricultural practices. Such events are referred to as the “urban syndrome”, were human populations and developmental demands outpace ecosystem services. Traditional measurements of water quality (e.g. physicochemical and micro-nutrient assessments) and biological monitoring (e.g. South African Scoring System 5, SASS5) techniques for assessing ecosystem health have being widely used to reflect the ecological health and status of river systems. However these techniques have a number of challenges associated with their application. SASS5 which is used most prevalently in southern Africa for example, can only be applied in lotic systems, it is habitat dependent and finally (but arguably most importantly) it cannot identify the source of pollution inputs. Recent laboratory studies using stable isotopic ratios (δ15N and δ13C) of aquatic macrophytes (duckweed: Spirodela sp.) have shown successful differentiation between different N-sources and the mapping of temporal and spatial nitrogen dynamics in freshwater systems. Furthermore δ15N isotopic values of Spirodela sp. showed the capability to act as an early warning indicator of eutrophication, before the onset of aquatic ecosystem degradation. Therefore, this study aimed to field test the potential of sewage plume mapping using the stable isotopic values of Spirodela sp. and aquatic macroinvertebrates at nine study sites on the Bloukrans-Kowie River and ten study sites on the Bushman-New Year’s River systems in the Eastern Cape, South Africa. And more...
- Full Text:
- Authors: Motitsoe, Samuel Nkopane
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5945 , http://hdl.handle.net/10962/d1020819
- Description: The majority of river systems in developing countries like South Africa, are found in catchments areas that are densely human populated, therefore are subjected to intense land-use and developmental pressures. Anthropogenic nutrient pollution or the excessive addition of nutrients is one important type of stressors that river systems often experience through intense land-use, which includes poor waste management and agricultural practices. Such events are referred to as the “urban syndrome”, were human populations and developmental demands outpace ecosystem services. Traditional measurements of water quality (e.g. physicochemical and micro-nutrient assessments) and biological monitoring (e.g. South African Scoring System 5, SASS5) techniques for assessing ecosystem health have being widely used to reflect the ecological health and status of river systems. However these techniques have a number of challenges associated with their application. SASS5 which is used most prevalently in southern Africa for example, can only be applied in lotic systems, it is habitat dependent and finally (but arguably most importantly) it cannot identify the source of pollution inputs. Recent laboratory studies using stable isotopic ratios (δ15N and δ13C) of aquatic macrophytes (duckweed: Spirodela sp.) have shown successful differentiation between different N-sources and the mapping of temporal and spatial nitrogen dynamics in freshwater systems. Furthermore δ15N isotopic values of Spirodela sp. showed the capability to act as an early warning indicator of eutrophication, before the onset of aquatic ecosystem degradation. Therefore, this study aimed to field test the potential of sewage plume mapping using the stable isotopic values of Spirodela sp. and aquatic macroinvertebrates at nine study sites on the Bloukrans-Kowie River and ten study sites on the Bushman-New Year’s River systems in the Eastern Cape, South Africa. And more...
- Full Text:
Quantifying the water savings benefit of water hyacinth (Eichhornia crassipes) control in the Vaalharts Irrigation Scheme
- Authors: Arp, Reinhardt
- Date: 2016
- Language: English
- Type: Thesis , Masters , MEcon
- Identifier: http://hdl.handle.net/10962/409 , vital:19956
- Description: Global fresh water resources are under increasing pressure from an ever-growing population and global economic development, highlighting the need for sustainable water management. Effective sustainable management must also control any additional factors that may aggravate the water scarcity problem. Invasive alien plants present such an aggravating threat, and pose a particular problem for water scarce countries in particular. South Africa is not immune to this global phenomenon, with plant invasions estimated to carry an annual loss of R5.8 billion in water provisioning services. Given the country’s semi-arid climate, and relative water scarcity, the threat presented by invasive plants needs to managed effectively for the sustainability of the countries already scarce fresh water resources. One species in particular, water hyacinth (Eichhornia crassipes), is regarded as one of the most destructive aquatic weeds in the world. The threat presented by this weed is of particular concern for economically productive water resources, such as irrigation water. Through high levels of evapotranspiration, water hyacinth leads to substantial water losses that could otherwise have been used more productively, thereby creating an externality on irrigation fed agriculture. An economic valuation of irrigation water and the loss thereof from water hyacinth, is a step towards improved water management and alien plant control. This will provide policy makers, stakeholders and irrigation managers with the relevant information they need to improve sustainability, allocate scarce resources more efficiently and enhance the returns to water. This thesis provides such an evaluation of the benefits of water hyacinth control, using the Vaalharts Irrigation Scheme as a case study. The benefit of water hyacinth control programmes are essentially ‘avoided costs’ of no control. The study quantified the water saving benefits of water hyacinth control for the Vaalharts Irrigation Scheme at Warrenton Weir on the Vaal River, South Africa. Three evapotranspiration to evaporation (ET:EW) ratios at three levels of invasion (100; 50 and 25% cover) were used to estimate the net annual water loss at Warrenton Weir. A Residual Value Method was employed to estimate the average production value of irrigation water, to serve as a proxy for the value of water lost via evapotranspiration by water hyacinth. The average production value of irrigation water for the Vaalharts was estimated to be R300/m3, which translated into an annual benefit of between R500 million and R9 billion. However, due to various limitations associated with the valuation method, the inflationary bias of estimating the average value of water and the unlikelihood of ET:EW ratios being larger than 1.4 in reality, it was suggested that R500 million was the more realistic value of the benefit of control. Despite being a conservative estimation, the benefit still equated to a quarter of the annual production value of the irrigation scheme, suggesting the water hyacinth could potentially reduce the productivity of the scheme by as much as 25% in the event of a scarcity of water on the scheme. The results of this research highlight the need for invasive plant control, especially where invasions affect economically productive water resources. Therefore, it is recommended that alien plant control policy prioritise invasions of this nature, as they present significant costs to the economy yet carry substantial benefits.
- Full Text:
- Authors: Arp, Reinhardt
- Date: 2016
- Language: English
- Type: Thesis , Masters , MEcon
- Identifier: http://hdl.handle.net/10962/409 , vital:19956
- Description: Global fresh water resources are under increasing pressure from an ever-growing population and global economic development, highlighting the need for sustainable water management. Effective sustainable management must also control any additional factors that may aggravate the water scarcity problem. Invasive alien plants present such an aggravating threat, and pose a particular problem for water scarce countries in particular. South Africa is not immune to this global phenomenon, with plant invasions estimated to carry an annual loss of R5.8 billion in water provisioning services. Given the country’s semi-arid climate, and relative water scarcity, the threat presented by invasive plants needs to managed effectively for the sustainability of the countries already scarce fresh water resources. One species in particular, water hyacinth (Eichhornia crassipes), is regarded as one of the most destructive aquatic weeds in the world. The threat presented by this weed is of particular concern for economically productive water resources, such as irrigation water. Through high levels of evapotranspiration, water hyacinth leads to substantial water losses that could otherwise have been used more productively, thereby creating an externality on irrigation fed agriculture. An economic valuation of irrigation water and the loss thereof from water hyacinth, is a step towards improved water management and alien plant control. This will provide policy makers, stakeholders and irrigation managers with the relevant information they need to improve sustainability, allocate scarce resources more efficiently and enhance the returns to water. This thesis provides such an evaluation of the benefits of water hyacinth control, using the Vaalharts Irrigation Scheme as a case study. The benefit of water hyacinth control programmes are essentially ‘avoided costs’ of no control. The study quantified the water saving benefits of water hyacinth control for the Vaalharts Irrigation Scheme at Warrenton Weir on the Vaal River, South Africa. Three evapotranspiration to evaporation (ET:EW) ratios at three levels of invasion (100; 50 and 25% cover) were used to estimate the net annual water loss at Warrenton Weir. A Residual Value Method was employed to estimate the average production value of irrigation water, to serve as a proxy for the value of water lost via evapotranspiration by water hyacinth. The average production value of irrigation water for the Vaalharts was estimated to be R300/m3, which translated into an annual benefit of between R500 million and R9 billion. However, due to various limitations associated with the valuation method, the inflationary bias of estimating the average value of water and the unlikelihood of ET:EW ratios being larger than 1.4 in reality, it was suggested that R500 million was the more realistic value of the benefit of control. Despite being a conservative estimation, the benefit still equated to a quarter of the annual production value of the irrigation scheme, suggesting the water hyacinth could potentially reduce the productivity of the scheme by as much as 25% in the event of a scarcity of water on the scheme. The results of this research highlight the need for invasive plant control, especially where invasions affect economically productive water resources. Therefore, it is recommended that alien plant control policy prioritise invasions of this nature, as they present significant costs to the economy yet carry substantial benefits.
- Full Text:
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