Doctoral Degrees (Conservation Ecology and Entomology)

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Abiotic and biotic drivers of African aquatic insect distribution
(Stellenbosch : Stellenbosch University, 2020-03) Deacon, Charl; Samways, Michael J.; Pryke, James S.; Stellenbosch University. Faculty of AgriSciences. Department of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Freshwater habitats are disproportionately rich in biodiversity, and are among the most threatened, yet poorly protected ecosystems. Aquatic insects make up much of the total freshwater fauna and contribute greatly to ecosystem functioning. At the broad-scale, aquatic insect distribution is driven by combinations of traits, as well as regional climate gradients and historical landscape context. Locally, both aquatic insect species richness and diversity are driven by various aspects related to vegetation and to physiochemical environments. Effective conservation requires thorough understanding of species distribution patterns at various spatial scales. My overall aim here is to combine broad-scale, theoretical biogeography, and local-scale empirical ecology to investigate drivers of aquatic insect distribution across Africa. Species are often binarily classified as ‘widespread generalists’ or ‘narrow-range specialists’ based on their ecological traits. Results in Chapter 2 show that ecological and biological traits are highly interactive among dragonflies, and inferring geographical range size based on ecological preference and/or biotope specialization alone should be approached with caution. Biological traits related to phenology and mobility were also strong drivers of dragonfly range size, indicating that conservation efforts should include multiple species across all habitat types. Regional climates show considerable variation across latitudinal and longitudinal gradients, and determine areas of high species richness and diversity. In Chapter 3, I show strong latitudinal and longitudinal gradients for South-African dragonfly species richness and endemism. Dragonfly assemblage-turnover boundaries coincided with significant geographical features and/or areas where contemporary climate changed from one condition to another. However, these dragonfly assemblage turnover-boundaries were gradual rather than discrete throughout South Africa. At the local scale, natural and artificial ponds contribute greatly to overall biodiversity, especially when they are of high quality and occur in networks across the landscape. I show that ponds characterized by high heterogeneity support diverse aquatic insect assemblages (Chapters 4 and 5). Chapter 4 showed artificial reservoirs, occurring alongside natural ponds in ecological networks, to expand the area of occupancy for most widespread dragonflies, aquatic beetles and true bugs. Some species with specific habitat requirements were confined to natural ponds, suggesting the significance of natural ponds for conserving the full range of insects. Dragonflies, aquatic beetles and true bugs occupy low-quality artificial reservoirs at low abundance to survive the adverse effects of drought (Chapter 5). However, many insects exclusively occupied natural ponds, emphasizing the overall importance of naturalness, and suggests that there is merit in improving artificial reservoirs. This would most likely be by having macrophytes and vegetated banks similar to those of natural ponds.Investigating aquatic insect distribution patterns is important for conservation, and here, I demonstrate the value of dragonflies as model organisms for investigating the drivers of broad-scale distribution patterns. Studying other taxa is also appropriate, as I have demonstrated at the local scale, but not always possible due to limited distribution knowledge. I recommend broad-scale investigations of other complementary taxa to determine their added value for elucidating the drivers of overall insect distribution patterns, and so address our current shortfalls to improve insect conservation.
Acoustic profiling of the landscape
(Stellenbosch : Stellenbosch University, 2014-04) Grant, Paul Brian Charles; Samways, Michael J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Soft, serene insect songs add an intrinsic aesthetic value to the landscape. Yet these songs also have an important biological relevance. Acoustic signals across the landscape carry a multitude of localized information allowing organisms to communicate invisibly within their environment. Ensifera are cryptic participants of nocturnal soundscapes, contributing to ambient acoustics through their diverse range of proclamation songs. Although not without inherent risks and constraints, the single most important function of signalling is sexual advertising and pair formation. In order for acoustic communication to be effective, signals must maintain their encoded information so as to lead to positive phonotaxis in the receiver towards the emitter. In any given environment, communication is constrained by various local abiotic and biotic factors, resulting in Ensifera utilizing acoustic niches, shifting species songs spectrally, spatially and temporally for their optimal propagation in the environment. Besides the importance of Ensifera songs from an ethological point of view, the multitude of species-specific signals provide an acoustic tapestry representing species diversity across ecological gradients and over time. Acoustic inventorying and monitoring of the landscape can reflect the environmental status of ecological systems, from natural to disturbed by human influence. In contrast to traditional survey techniques, sound recording and interpretation is a non-invasive method that allows for the detection and classification of highly cryptic, yet insightful indicators of ecosystem change. Here, acoustic monitoring was used across diverse ecological gradients to improve understanding of species diversity patterns, and how they change in response to both natural gradients and in response to the human dominated landscape mosaic. This study was undertaken in three geographic locations from tropical rain forest of Brunei, Borneo, to the landscapemosaic of plantation forestry in KwaZulu-Natal, South Africa, and to the botanically rich, mountain fynbos region of the Cape Floristic Region, also in South Africa. Each region provided a diverse and particular landscape to test the value of acoustic surveys for determining local diversity patterns across natural gradients and to assess the value of the technique for assessing the impact human influence across landscapes. In tropical rainforests, an entire acoustic guild was investigated to determine how acoustic species partition their acoustic communication channels spectrally, temporally and spatially, to avoid acoustic interference. The overall assemblage showed considerable spectral partitioning. Diurnally active species showed low temporal niche overlap, whereas nocturnal species did not utilize temporal partitioning. Lack of nocturnal temporal partitioning suggests other mechanisms of acoustic avoidance are sufficient to avoid acoustic overlap, or that there are insufficient cues to partition nocturnal acoustic environments. Acoustic species also utilized spatial partitioning, with distinct acoustic assemblages at vertical heights and with elevation. Utilization of a range of different strategies allow many species to communicate with conspecifics with little or no interference from other species in a signal rich environment. Acoustic profiling was also undertaken in KwaZulu-Natal, South Africa, across a plantation forestry landscape mosaic with diverse ecological gradients containing both alien and indigenous vegetation, as well as boarding large natural protected areas. Areas covered in alien timber or non-endemic grass were devoid of acoustic signals. Managed areas that were mowed and heavily grazed were not effective in maintaining the natural complement of nocturnal acoustic species. Within natural vegetation patches inside plantations, acoustic species richness increased with plant heterogeneity and patch size. Patches of indigenous vegetation within the plantation matrix effectively reduced the contrast of transformed landscapes with surrounding natural areas, with indigenous forest patches containing a highly characteristic acoustic species assemblage. Within the botanically rich, mountain fynbos region of the Cape Floristic Region, acoustic profiling was conducted across gradients of elevation, season and vegetation. Across these gradients, katydid acoustic signals were identified and characterized for the first time. This resulted in the discovery of two new katydid species and a novel sound producing structure in a carabid beetle, a species previously unknown to produce sound. Acoustic diversity across seasonal and elevational gradients increased with increasing temperatures. Climatic variability along the elevational gradient produced variation in seasonal phenology. Katydids also utilized high frequency acoustic signals, which is probably an adaptation to overcome background noise from wind, so prevalent in this area. Furthermore, despite producing conspicuous signals for mate attraction and pair formation, katydids were found not to be part of bat-eared fox diet, an insectivorous, nocturnal predator that uses its characteristic large ears to detect sounds made by invertebrate prey. This study shows the value of using acoustic emissions from katydids to identify acoustic diversity patterns across ecological gradients and in response to human impacts on the landscape.
Agrohidrologiese studies aan die Olifantsrivierbesproeiingskema, 1959-1962
(Stellenbosch : Stellenbosch University, 1962) Nieuwoudt, Alexander Daneel; Sim, J. T. R.; Stellenbosch University. Faculty of AgriSciences. Department of Conservation Ecology and Entomology.
No Abstract available.
Applying a resilience approach to flood management in rapidly changing landscapes
(Stellenbosch : Stellenbosch University, 2016-12) Ilse, Kotzee; Reyers, Belinda; Esler, Karen J.; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Human land use activities have significantly changed the capacity of ecosystems to deliver essential service. Additional stresses brought about by climate change will require a shift in how ecosystems are managed. Global increases in the magnitude and frequency of flood events in particular have raised concerns that traditional flood management approaches may not be sufficient to deal with future uncertainties. Resilience approaches aimed at understanding and managing the capacity of social-ecological system (SES) to adapt to, cope with, and shape uncertainty and surprise offer a possible avenue to deal with these challenges. Accordingly, through the use improved systems approaches and knowledge on floods, flood regulation services and its impact on people and infrastructure this dissertation contributes towards developing and piloting of a flood resilient management strategy. Research was carried out using three flood prone municipalities in the Eden District of South Africa as a case study. The Millennium Ecosystem Assessment, in its final report, highlighted regulating services as some of the most important and degraded, but least understood ecosystem services. Regulating services moderate the flow of energy and materials and play a critical role in regulating the impacts of extreme events. The progress in research and understanding of regulating services was investigated, with a particular focus on progress on their assessment and quantification. Findings flag key research gaps in all regulating services in developing countries and globally, in specifically understudied regulation services of disease regulation and air quality regulation. Results also revealed the need to include the human dimension into the study of regulating services, which will require an increase of multi-disciplinary research using a social-ecological system approach. Based on these findings and the objectives of the study the use of an existing decision support tool SCIMAP was adapted and explored using globally available data to provide a practical and informative approach for identifying flood receiving areas at a watershed scale. Model outputs highlighted how the combined effect of natural and anthropogenic factors can aggravate or attenuate a flood event, adding valuable insights into flood generation and how it can be managed, especially in under resourced areas. In order to assess the resilience of communities to floods, a composite index and spatial analysis approach was piloted. The approach allows for a simple, yet robust index able to include an array of datasets generally available in flood prone areas with potential to disaggregate and trace variables for management and decision making. Finally, based on the methods and results developed in previous chapters of the dissertation, an approach to characterise and spatially connect the flood regulating ecosystem service flows from supply to demand is introduced and illustrated. The proposed method builds on from the thinking in flood vulnerability and incorporates landscape connections from supply to demand areas. By identifying and linking supply areas to the downstream benefitting areas of the watershed, areas directly linked to high demand can be conserved to ensure a sustainable supply of the flood regulation service. This dissertation provides new and improved approaches for building and managing flood resilient watersheds. The results have immediate applicability to landscape managers in areas where data for process-based models and the capacity to interpret model outputs may be limited.
Arthropod communities of Proteaceae with special emphasis on plant-insect interactions
(Stellenbosch : Stellenbosch University, 1989) Coetzee, J. H.(Jacobus Hendrik); Giliomee, J. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology & Entomology.
ENGLISH ABSTRACT: Arthropod communities of five proteaceous species viz. Protea repens. P. neriifolia. P.cynaroides, Leucospermum cordifolium and Leucadendron /aureolum were studied. A faunal list of the insects was compiled according to the feeding guilds of insects. Six phytophagous guilds were recognized: flower visitors, thrips, endophages, ectophages, sap-suckers, and ants. The guild composition, species packing and seasonal distribution for the free-IMng insects, spiders and other arthropods were investigated on the different plant species. The ants, flower visitors and sap-sucking species found on the plant species, were very similar, but the number of leaf chewing species common to all the plant species was low, suggesting that some species were monophagous. Insect abundance increased during the wet winter months when the plants were in flower. Of the total number of herbivores collected, flower visitors represented 69,5%, leaf feeders 14,5% and sap-suckers 16,1 %. The chewers constituted 60,1% of the total herbivore. biomass. Leaf damage increased with age ; young leaves were practically free of herbivore damage, while older leaves were stm acceptable as food. The degree of insect damage differed amongst the plant species varying from 2% to 15%. The following leaf characteristics were investigated to determine the factors involved in defence against insect herbivory : total phenolic content, protein precipitating ability, cyanogenesis, nitrogen content, leaf toughness, woodiness and fibre content lt appears that the plant species use different mechanisms to protect their leaves. The infructescences of Protea repens were exploited by the larvae of four Coleoptera and four Lepidoptera species. The community structure of these phytophagous insects was determined largely by negative interactions. Various strategies are followed (e.g. niche segregation in time and space) to lessen interspecific competition.
Assessing the role of natural open spaces in ecosystem service provision for enhanced urban planning in the global south
(Stellenbosch : Stellenbosch University, 2022-04) Wessels, Nadia; Esler, Karen J.; Sitas, Nadia; O'Farrell, Patrick; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Natural open space plays an important role in maintaining biodiversity and providing essential ecosystem services, i.e. the contributions we get from nature. Yet, natural systems within urban areas continue to be exploited and encroached upon, and are often undervalued in urban planning and management decisions, particularly within the context of the Global South where institutional constraints, and complex socio-economic and political priorities prevail. In response to these challenges, this research assessed the role of natural open space in ecosystem service provision for enhanced urban planning in the Global South, by using a case study of the Nelson Mandela Bay Municipality, situated in the Eastern Cape Province, South Africa. The research explored how understanding the benefits (ecosystem services) derived from natural open space can optimise and improve planning, which can, in turn, enable more people to benefit from the ecosystem services provided in cities. Urban natural open space systems form part of complex adaptive social-ecological systems. The realisation and optimisation of the ecosystem services provided by natural open space systems require an understanding of how land cover change affects ecosystem services, and consideration of implementation challenges and opportunities related to mainstreaming ecosystem services into urban planning, which include community and local government needs and priorities within the socio-economic and political context. Developing and implementing natural open space plans requires a transdisciplinary approach that moves beyond disciplines, such as the natural and social sciences only, to incorporate other ways of knowing and feedbacks between different knowledge systems, for example, linking practitioners’ and indigenous and local knowledge, where context-specific human needs, attitudes and values are recognised. The multidimensional outcomes of implementing urban conservation plans (or natural open space plans) are rarely critically evaluated. By providing a framework for monitoring and evaluating conservation outcomes and understanding the causal linkages and reasons for the success and failure of conservation outcomes, this research facilitates the institutionalisation of adaptive management approaches, enhancing urban planning and conservation and social outcomes. Through qualitative interviews with community members representing the city’s diverse socio- economic and ethnic variability (living near natural open space), the complex relational values with nature, and nuanced interpretations of how natural open space delivers ecosystem services were explored. Non-material services (relational benefits) were impacted by exploitative material uses, access concerns, and (mis)management. Management of natural open space also has significant implications for intra and inter-generational equity in respect of the benefits of ecosystem services, and the experience of ecosystem disservices, which require explicit consideration in municipal planning, budgeting and management. Innovative collaborative management and stewardship interventions with ecological and socio-economic benefits should be prioritised to protect the natural open space system. In the Global South the benefits of urban nature in terms of the supply and provision of ecosystem services are inequitably distributed and intertwined in complex socio-political processes. The degree to which the ecosystem services provided by natural open space are valued by local government officials, planned for, prioritised, and incorporated in decision- making, in terms of temporal and spatial implications, need to be understood. Institutional constraints of many local governments in the Global South, such as data and resource capacity, inhibit the appropriate consideration and incorporation of ecosystem services into urban planning. In such instances, expert (scientific) knowledge should be used to contribute to understanding the context-specific diverse ecosystem services provided by natural open space, and the implications of land cover changes on ecosystem service provision associated with rapid urbanisation. This expert understanding then needs to be incorporated with other knowledge systems. The research has emphasised the collective role of community members, civil society and the private sector; city officials and decision-makers; and scientists and researchers in the effective integration of ecosystem services into urban planning, in steering cities towards a sustainable trajectory. There is no panacea for effectively integrating ecosystem services into urban planning. Instead, advancing ecosystem services in urban planning requires various context-specific initiatives and approaches, which allow for collaborative governance and innovative nature-based solutions, and which give due consideration to intra and inter- generational equity. The research identifies opportunities for how to incorporate and catalyse stewardship for natural open space systems and contextually appropriate interventions that could be employed in other cities. It also highlights the need to understand the implications of trade-offs associated with the socio-economic drivers of land transformation over ecosystem service retention as cities in the Global South continue to grow and develop. The methodology followed in this research shows that an understanding of urban ecosystem services is possible without expensive and / or data-intensive decision-making tools, and similar approaches could be followed in other under-resourced cities in the Global South, which can then be used to enhance urban planning.
An assessment of different beekeeping practices in South Africa based on their needs (bee forage use), services (pollination services) and threats (hive theft and vandalism)
(Stellenbosch : Stellenbosch University, 2017-03) Masehela, Tlou Samuel; Veldtman, Ruan; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Two honey bee subspecies indigenous to South Africa, Apis mellifera capensis Escholtz (Cape honey bee) and Apis mellifera scutellata Lepeletier, are actively managed by beekeepers for honey production, other bee related products (e.g. bees wax) and to provide pollination services. Historic records show that managed colonies of both subspecies to rely on a mix of exotic - (Eucalyptus species, agricultural crops, weeds and suburban plantings) and indigenous forage (genera and vegetation units). However, their extent of use and importance for honey production, pollination, colony maintenance and swarm trapping (together referred to as beekeeping practices), have not been fully explored across South Africa. Additionally, acts of hive theft and vandalism have become a key concern for the industry, threatening and potentially limiting beekeeping in some areas. Related to this is also a concern that growers need more colonies for crop pollination than beekeepers can supply. Furthermore, beekeepers currently face challenges related with their industries’ organisation and governance. The broad aim of my study was to understand the multiple challenges facing the South African beekeeping industry and to contribute detailed knowledge on forage use for beekeeping practices in South Africa. The knowledge thereof would provide a practical understanding of these aspects and ultimately contribute towards the planning and decision making where beekeeping is concerned. Using two questionnaire surveys I determined: 1) the current status of beekeeping in South Africa based on beekeeper opinion; 2) forage use for honey production; 3) the use and demand for pollination services; 4) forage use for colony maintenance and swarm trapping; and 5) trends and implications of hive theft and vandalism for the beekeeping industry. The forage use survey captured the most managed colonies (50067) and respondents (218) compared to the hive theft and vandalism survey, which had 161 respondents constituting 48386 managed colonies. Results showed that beekeepers have concerns similar to those captured in previous studies and reports, with the lack and loss of forage being very important. Across all four beekeeping practices exotic forage was predominantly used, although the level of preference differed provincially. The important forage types and significant species were highlighted in each province on the basis of number of colonies using individual forage species and followed a similar trend to that of forage categories. Some species were both important and of significant use for more than one beekeeping practice (e.g. Eucalyptus grandis, Eucalyptus cladocalyx, Helianthus annuus, Macadamia spp. and Senegalia mellifera) in the same or different provinces. The preference of trapping swarms on different forage highlighted the value of this practice compared to hive splitting, removal of problem swarms and buying of colonies from other beekeepers. Also, the number of localities used for forage differed across provinces, although in some cases the same locality was used for more than one beekeeping practice. Furthermore, some beekeepers used localities situated in their neighbouring provinces. These results suggest that exotics remain the predominantly used forage source for beekeeping in South Africa, and that some forage types and sources are more important that others in their respective localities. Also, provinces have different forage needs in relation to the different beekeeping practices. Therefore, the planning, management and promotion of bee forage at regional or national level should consider all four practices. It was challenging to obtain reliable planting data (given in hectares) and number of colonies used for pollination per hectare for respective crops. This prohibited a thorough understanding of the relationship between pollination service provision and demand, highlighting the importance of formally capturing this data. However, the derived results indicated pollination demands to be stable at a national level while inconclusive for certain provinces (e.g. Free State). The Western Cape had the highest pollination demand overall, while crops such as oil seeds, deciduous-, subtropical fruit, and nuts had high pollination demands. Trends in hive theft and vandalism showed most losses to occur through human induced vandalism. Although the magnitude of losses varied between provinces, factors contributing to the losses were similar with respect to the positioning (agricultural lands) and visibility (medium) of the colonies within the landscape. This means that for these colonies to continue accessing forage for various beekeeping practices, various sites need to be protected from theft and vandalism.
Assessment of farming systems and cover configuration options that enhance natural regulation of herbivorous arthropod abundance in maize-fields
(Stellenbosch : Stellenbosch University, 2018-12) Otieno, Nickson Erick; Jacobs, Shayne Martin; Pryke, James S.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Maize, Zea mais, is grown globally and is a leading staple crop in sub-Saharan Africa, where it crucially sustains many household economic and nutritional needs, and the continent’s food security. However, its production is curtailed by damage from a range of herbivorous arthropods, undermining its potential to fulfil increasing demand from a growing population. In Kenya, maize is produced primarily by small-scale subsistence farmers who have limited economic capacity for commercially-based arthropod herbivore control. Whereas the scale of future crop arthropod damage is projected to increase due to global warming, low economies of operational scale undermine many farmers’ ability to increase their response investment to forestall anticipated crop losses. This calls for measures for crop-field arthropod control that are affordable yet affective for sustainable maize production. I investigated a range of agronomic management practices that may be applied in fostering natural suppression of arthropod herbivore abundance across 16 non-Bt maize-fields in western Kenya. I assessed how structural configurations and cover elements including hedgerows, on-farm trees, crop-cover patterns, woodlots and maize cover proportion enhance farm-level habitat complexity to attract predatory arthropods and insectivorous birds for top-down suppression of herbivorous arthropods. I compared effects of these variables on abundance, richness and diversities of arthropod and birds species between organic and conventional farming systems and between monocultured maize versus maize inter-cropped with legume crops. To assess potential for herbivorous arthropod reduction rates, I analysed δ13C and δ 15N stable isotope signatures to track maize carbon through herbivorous arthropods to arthropod predators, and also established a bird exclusion experiment to test insectivorous birds’ contribution to reducing arthropod abundance. By grouping farms into structural clusters, I further tested how arthropod and bird assemblage turnovers differed between local farm-level and wider spatial scales and along a heterogeneity gradient. Organic rather than conventional farming was more supportive of local-scale arthropod abundance, together with inter-copping, but not at wider spatial levels. However, organic farming was less important than crop diversity in boosting insectivorous bird abundance and richness. Herbivorous arthropods were significantly attracted to fields with higher maize cover proportions especially on conventional farms, suggesting susceptibility of monocultured maize to proliferous arthropod herbivory. Higher hedgerow volume, tree densities and larger woodlots enhanced all arthropod guild and bird aggregations at both spatial scales. Although the bird exclusion experiment proved insectivorous birds’ linkage to herbivorous arthropod suppression at local-farm level, this effect was not evident at wider spatial scales. Stable isotope analyses revealed a stronger predator-herbivore trophic linkage under inter-cropping systems, with lepidopteran herbivores the most significant consumers of both maize and legumes. On the other hand, ants showed the best capacity to suppress maize-consuming arthropods while wasps and beetles would best reduce legume consumers. The findings demonstrate that there is a wide range of farm-level habitat management practices for enhancing habitat complexity to boost natural top-down herbivore suppression across maize-fields, but greater effectiveness is achievable through synergistic application of measures rather than individualistic approaches. Furthermore, a multi-spatial scale strategy in applying appropriate techniques would maximize landscape resilience against herbivorous arthropods.
Beta diversity across the complementary zones of the Kogelberg Biosphere Reserve
(Stellenbosch : Stellenbosch University, 2019-04) Van Schalkwyk, Julia; Pryke, James S.; Samways, Michael J.; Gaigher, Rene; Stellenbosch University. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Biodiversity loss is occurring at an alarming rate. Protected areas alone are not sufficient for long-term biodiversity conservation. To address this, conservation efforts need to incorporate the landscape surrounding protected areas. Biosphere reserves (BR) consist of three zones with different (but complementary) functions: a core area (dedicated specifically to long-term biodiversity conservation), an adjoining buffer zone (where activities should be compatible with the objectives of the core), and a flexible transition zone (where sustainable resource use and management is promoted). Zonation will generally match existing land-use patterns, and the buffer forms part of a continuous but increasing gradient of land-use intensity (LUI) as one moves away from the core. The aim of this study is to assess the success of biodiversity conservation of the different zones of the Kogelberg Biosphere Reserve (KBR) in response to increasing LUI away from the core. I focused on commercial fruit farming, since it is an important economic activity in the study area. I chose objectives that are related to the ecological function of each zone using arthropods as study organisms, and employed principles based on systematic conservation planning (SCP) and landscape ecology. The specific objectives were: 1) to determine whether arthropod diversity tracks plant diversity, 2) assess how well arthropod diversity is represented in the core zone, 3) to determine whether the buffer zone is effective in protecting the core from activities in the transition, 4) to assess whether the buffer zone complements arthropod diversity in the core zone, 5) to assess how orchards influence arthropod diversity in adjacent non-crop habitats, and 6) to determine how LUI at different spatial scales affects arthropod diversity within orchards. The results showed that arthropod diversity is relatively well-represented within the core zone, but that the buffer has important complementary value by adding ecological environments not present in the core. The buffer also improves the comprehensiveness of the reserve by establishing strong environmental gradients (which are important for congruence in plant and arthropod diversity). The KBR does not have a continuous buffer surrounding its core area, and this was reflected by the influence of anthropogenic activities (i.e. proximity to deciduous fruit orchards) on diversity in the core zone. This influence reached up to 1 km away from orchards, decreasing the effective conservation area of the core zone where the buffer is absent or not wide enough. Closer investigation showed that the observed edge responses were the result of differential responses of different arthropod groups, and that they could be predicted by traits related to species habitat specialization (species which prefer natural habitats, species which prefer orchards, and species which occur in either). The results highlighted the variegated nature of the transformed landscapes that is not captured by patch-orientated views of fragmentation. This study also emphasises the importance of management actions within orchards on diversity in adjacent habitats and the associated non-visible heterogeneity. Arthropod diversity in orchards showed contrasting responses to increasing LUI at different spatial scales. Local LUI (management intensity) had a negative influence on some groups. Landscape scale LUI (in the form of more orchards in the landscape) increased species richness of a subset of species, and contributed to the homogenization of orchard arthropod diversity across the landscape. This highlights the need to consider the influence of LUI on diversity at different spatial scales. Principles from SCP and landscape ecology are valuable for prioritizing conservation efforts, and for guiding planning and management towards promoting biodiversity across the entire landscape. To enhance arthropod diversity across the KBR, the most important recommendations from this study are to include a range of abiotic variables (especially variables related to climate and geology) in conservation areas. This implies conservation efforts should not be restricted to only the core zone. While LUI was important in determining diversity at the local scale, non-crop habitats are essential for enhancing farmland diversity across the entire BR.
Biodiversity assessments using remote sensing and integrative modelling for improved conservation management
(Stellenbosch : Stellenbosch University, 2022-04) Theron, Kasselman Jurie; Pryke, James Stephen; Samways, Michael John; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Insect diversity is declining globally, threatening ecosystem collapse and human well-being. Accurate information on biodiversity dynamics is needed to guide landscape management. This is important within actively managed production landscapes (especially forestry and agriculture), where land use change and habitat degradation impacts biodiversity, which in turn influences ecological resilience. Satellite remote sensing allows for collection of data over time, which enables a greater understanding of species distributions and drivers of change. Combining satellite-derived variables with advanced integrative modelling approaches, such as time series analysis, habitat suitability modelling, functional connectivity analysis and deep learning image fusion, allows for better understanding of biodiversity dynamics to guide landscape management. In this dissertation, I focus on grasshoppers, indicators of high-quality grasslands, and study their diversity within grassland corridors between plantation forests, to gain a greater understanding of how plantation landscapes can be managed (e.g. prescribed burning, invasive plant management, tree harvesting) to ensure ecological resilience. Satellite time series showed that changes in grassland structure can have a lasting positive impact on grasshoppers for up to three years. Prescribed burning, measured using historic Normalised Burn Ratio index, helps maintain high-quality grasshopper habitat, while also influencing functional connectivity of grassland corridors. Normalised Difference Vegetation Index (NDVI) was a useful tool to monitor grassland corridor condition and to assist with planning of prescribed burning. Large corridors with an elevation gradient support diverse assemblages and should be prioritised for conservation. Deep learning image fusion classified American bramble (Rubus cuneifolius), an aggressive invasive species in South African grasslands, with high accuracy compared to conventional satellite imagery. Bramble had negative impact on plant species richness, larger-sized grasshopper species, as well as species of conservation concern. Bramble invaded riparian areas more frequently, threatening Ensifera grasshopper species habitat. Harvesting timber compartments and prescribed burning increased bramble cover within the landscape. Active management of plantation tree saplings after harvesting can lead to enhanced functional landscape connectivity and reduced bramble cover. Grassland corridors have high vegetation heterogeneity caused by prescribed burning, which contribute to high species turnover. Corridors should be burned every 2-3 years. Using NDVI will help foresters to identify where and when to burn corridors, thereby maintaining high-quality grasshopper habitat and functional connectivity. Rotational harvesting of timber compartments is recommended, as logging only some compartments will have positive impact on functional connectivity as well as helping prevent bramble invasion through the landscape. I recommend combining prescribed burning with grazing by domestic cattle to control bramble invasion. Special attention is needed to control bramble two years after harvesting, as this is when bramble cover is highest. This dissertation demonstrated that grassland corridors maintain biodiversity within actively managed production landscapes when management incorporates biodiversity response to disturbance. This motivates for the maintenance and protection of grassland corridors in other parts of the world to conserve biodiversity and help address insect decline. Lastly, the techniques used here provide valuable insights into biodiversity response to actively manage landscapes, and can therefore be applied to other vegetation types for protecting biodiversity.
The biogeomorphology associated with a keystone plant species in the sub-Antarctic
(Stellenbosch : University of Stellenbosch, 2011-03) Haussmann, Natalie Suzette; McGeoch, Melodie A.; Boelhouwers, Jan C.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
AFRIKAANSE OPSOMMING: Min aandag is al gegee aan biogeomorfologiese interaksies in glasiale en periglasiale omgewings. Nietemin is hierdie interaksies, wat op die skeidingsvlak tussen ekologie en geomorfologie fokus, baie belangrik in hierdie omgewings, waar organismes in noue verband met die abiotiese omgewing saamleef. In hierdie tesis bestudeer ek die interaksies tussen die vaskulêre plantspesies met die hoogste voorkoms op sub-Antarktiese Marion Eiland, Azorella selago Hook. (Apiaceae), en die omringende geomorfologiese landskapsvorme, -prosesse en meettegnieke. Verder verskaf die tesis voorstelle om toekomstige geïntegreerde biogeomorfologiese navorsing te vergemaklik. Om die gevolge van A. selago-plante vir sedimentbeweging en -verspreiding te verstaan, het ek die verspreiding van sedimentgroottes om hierdie plante gemeet deur middel van 'n kombinasie van fotografiese analise-metodes. Deur as sedimentbewegingsobstruksies te dien, het plante 'n waarneembare effek op die omringende sedimentverdeling. Dit is veral belangrik om hierdie interaksies tussen A. selago en sy omgewing te verstaan in die lig van onlangse klimaatsverandering op die eiland, omdat sedimentgrootte belangrike grondeienskappe soos waterretensiekapasiteit en vriesgevoeligheid beïnvloed. Om die effek wat A. selago plante op die omringende mikroklimaat het beter te verstaan, is die kleinskaalse variabiliteit in grondtemperature om A. selago plante bestudeer. Grootskaalse grondligting as gevolg van fors is gemeet, ten spyte van relatief ligte forseienskappe. Dit dui daarop dat naaldys ook by temperature bo -2°C kan vorm. Wintergrondtemperature aan die oostekant van plante was effens laer en minder veranderlik as aan die westekant van plante, waarskynlik as gevolg van laer windsnelhede en/of sneeu wat ophoop aan die oostelike, lykant van plante. Die resultate benadruk dat A. selago plante 'n belangrike rol speel in die verandering van mikroklimate en dat dit belangrik is om die gevolge van sulke veranderings, soos die skep van mikrohabitatte vir grondorganismes, te verstaan. Daar word vermoed dat positiewe plantinteraksies negatiewe interaksies oorheers in omgewings met hoe abiotiese druk. Gevolglik wys ek dat daar 'n positiewe verband bestaan tussen A. selago plante en saailinge van beide A. selago self, asook van die meerjarige gras Agrostis magellanica Lam. (Poaceae). Ek stel voor dat beide plante en klippe sade, wat deur wind, reenval en/of afdraande sedimenttransportering as gevolg van vriesprosesse vervoer word, opvang. Verder dui verhoogde A. selago saailinggetalle om plante, maar nie om klippe nie, daarop dat plante een of ander biologiese voordeel aan A. selago saailinge bied. Dit is bekend dat die verspreidingspatrone van plantspesies as gevolg van abiotiese stresgradiente varieër. Met hierdie bevinding in gedagte, is moontlike faktore verantwoordelik vir A. selago saailinggetalle en -verspreidingspatrone, soos hoogte bo seespieël en substraatbedekking, bestudeer. Alhoewel dit wil voorkom asof daar 'n verband tussen saailinggetalle en hoogte bo seespieël is, is saailinggetalle en verpreidings meestal afhanklik van ongemeette perseel-spesifieke eienskappe. Plante kan die omringende geomorfologie beïnvloed, maar ook geomorfologiese meettegnieke. Om die potensiaal van kosmogeniese dateringsmetodes as geomorfologiese hulpmiddels in fellfield habitatte te verken, is die akkumulasietempo van die kosmogeniese isotoop ¹ºBe onder en langs 'n A. selago plant bepaal. Die resultate dui daarop dat ¹ºBe nie ten volle in die grondprofiel behoue bly nie en verskeie potensiële redes word bespreek. Verder dui die resultate daarop dat ¹ºBe konsentrasies in fellfield habitatte versigtig geïnterpreteer moet word, aangesien A. selago plante effektief ¹ºBe opvang in hulle grondryke kern. Om vordering in biogeomorfologie te vergemaklik, is dit belangrik om bewus te wees van die verskillende metodes wat geomorfoloë en ekoloë volg. Ekologiese benaderings is dikwels op strenger statistiese tegnieke gebaseer, terwyl geomorfoloë eerder fokus op 'n meer beskrywende benadering en teoretiese beredenering. Ek verduidelik hoekom die twee velde sulke uiteenlopende benaderings volg, benadruk moontlike struikelblokke en verskaf voorstelle om samewerking te vergemaklik.
Biological and ecological factors contributing to the successful use of entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) for the control of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) under South African conditions
(Stellenbosch : Stellenbosch University, 2011-12) De Waal, Jeanne Yvonne; Malan, Antoinette P.; Addison, M. F.; Addison, Pia; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: Codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) is a devastating pest of pome fruit in temperate regions of the world. Control of this pest, previously involved the extensive use of broad-spectrum insecticides. However, concerns over human safety, environmental impact, widespread dispersal of resistant populations of codling moth and the sustainability of synthetic pesticides in agroecosystems, has encouraged the development and use of alternative environmentally-friendly pest management technologies including the use of entomopathogenic nematodes. These nematodes are lethal pathogens of insects and belong to the families Steinernematidae and Heterorhabditidae, and are ideal candidates for incorporation into the integrated pest management programme currently being developed for residue-free pome fruit production in South Africa. The biological and ecological factors pertaining to the successful use of these nematodes for the control of codling moth were investigated in this study. Their use for bin-disinfestations was evaluated, focusing on the optimum handling conditions to ensure the survival and subsequent efficacy of the nematodes. The study proved that the local isolate SF41 of Heterorhabditis zealandica Poinar 1990 could be used for successful bin-disinfestation. The use of the same nematode isolate was also investigated for the disinfestation of mulch layers of diapausing codling moth larvae. An insect containment device which allowed for direct trial efficacy evaluation was identified and ecological factors pertaining to the successful use of nematodes for mulch disinfestation were investigated. The biological control potential of local nematode isolates, which had previously never been tested against codling moth larvae, was investigated in the laboratory under conditions as can be expected during orchard applications. The efficacy of the selected isolates was confirmed in field experiments. Innovative insect containment methods for above-ground trial efficacy evaluation in the field were investigated. Desiccation proved to be the most limiting factor to the survival and subsequent efficacy of the nematodes during field applications in temperate regions. The effect of low moisture levels on H. zealandica’s efficacy to control diapausing codling moth larvae was subsequently investigated and a starch-based formulation was further tested to overcome the issue of desiccation. Conclusive results indicated that there were several biological and ecological factors influencing the survival of nematodes and illustrated how these factors could be manipulated to overcome these issues and thereby ensure the efficacy of treatments. This is the first report of its kind to comprehensively investigate the use of South African entomopathogenic nematodes for the control of diapausing codling moth larvae and all results emanating from the study can be integrated into a framework for the commercial use of these nematodes in this regard in future.
Biological control of the banded fruit weevil, Phlyctinus callosus (Schönherr), using entomopathogenic nematodes and fungi
(Stellenbosch : Stellenbosch University, 2018-11) Dlamini, Bonginkhosi; Addison, Pia; Malan, Antoinette P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The overall aim of this study was to establish guidelines, from research undertaken mainly in the laboratory, and from field application, for the use of entomopathogenic nematodes (EPNs) and entomopathogenic fungi (EPF) to control the banded fruit weevil (BFW), Phlyctinus callosus (Schönherr), in vineyards and apple orchards in the Western Cape province. Discovering new species of entomopathogens is important, as more virulent, locally adapted species can be used to increase the potential of microbial control. The first objective of this study was to survey for EPNs and EPF strains/species in orchards and vineyards of the Western Cape, and to investigate their potential to control the BFW. The most virulent EPN species for the biological control of the BFW were selected in laboratory bioassays, and a field trial using Steinernema yirgalemense at different concentrations was conducted. In a further study, the best EPF strains for the biological control of the BFW were selected in laboratory bioassays. The most virulent EPN and EPF isolates were applied, in combination, to determine their interaction-effect on the mortality of BFW in the laboratory, as the final objective. In total, 70 soil samples were collected from deciduous fruit orchards and vineyards in the Western Cape. The soil samples were baited with mealworms, Tenebrio molitor (Coleoptera: Tenebrionidae) to trap EPNs and EPF, which were characterised by using morphological and molecular techniques, and evaluated for their potential to control the BFW adults. EPNs were isolated from 17 % (12) of the samples, with Heterorhabditis bacteriophora Poinar and Heterorhabditis safricana as the only two EPN species isolated. Heterorhabditis bacteriophora (53 % mortality) resulted in significantly higher (p < 0.05) mortality of adult BFW, compared to H. safricana (37 % mortality), in laboratory trials. EPF were trapped from 37 % (26) of samples, consisting of a total of 14 Beauveria bassiana isolates and 12 isolates from the Metarhizium anisopliae complex. A Metarhizium isolate (79 % mortality) resulted in significantly higher (p < 0.05) mortality of BFW adults, compared to B. bassiana (63 % mortality) in laboratory trials. Results obtained from the study indicate that the soil samples from the deciduous fruit orchards and vineyards from the Western Cape contained both EPNs and EPF that can be used to control BFW. Different EPN species were evaluated by laboratory screening for virulence against the different life stages of the BFW. A field trial to determine the performance of Steinernema yirgalemense, applied at different concentrations, followed. Results from a probit analysis showed S. yirgalemense to be six times more potent than Heterorhabditis noenieputensis, giving 95 % mortality of BFW larvae at a concentration of 400 infective juveniles (IJ) per insect, which was significantly higher (p < 0.05) compared to other concentrations. At a concentration of 100 IJs/insect, Steinernema yirgalemense, H. noenieputensis, and Steinernema feltiae resulted in significantly higher (p < 0.05) mortality of BFW larvae compared to the other EPNs, with no significant difference between each other. Heterorhabditis indica (70 % mortality) and H. baujardi (67 % mortality) resulted in significantly higher (p < 0.05) mortality of the BFW pupae, compared to H. noenieputensis (55 % mortality). In the case of adult BFW, Heterorhabditis indica (95 % mortality) and S. yirgalemense (94 % mortality) gave significantly (p < 0.05) higher mortality, compared to three other EPN species evaluated. In the field trials, S. yirgalemense, at 20 and 40 IJs/cm2, gave 69 % and 78 % mortality of BFW larvae, respectively. The results showed that all EPNs screened controlled the juvenile and adults stages of BFW. Steinernema yirgalemense was also shown to be capable of controlling BFW under field conditions, even at low concentrations. Different Different EPF isolates were tested at 1 × 106 conidia ml-1 for their virulence against the different life stages of the BFW. Results showed that Broadband® (Beauveria bassiana strain PPRI5339) (97 %) and Meta 69 (Metarhizium anisopliae) (93 %) gave significantly higher (p < 0.05) mortality of BFW larvae compared to Eco-Bb® (B. bassiana) (58 %), with no significant difference in mortality between Broadband® and Meta 69. In the case of pupae, Broadband® (92 %) gave significantly higher (p < 0.05) mortality, compared to Eco-Bb® (67.5 % mortality) and Meta 69 (65.8 % mortality). Broadband® (90 % mortality) gave significantly higher (p < 0.05) mortality of adult BFW compared to Eco-Bb® (69.2 % mortality) and Meta 69 (65 % mortality), of which neither differed from each other. When compared to a local EPF (M. anisopliae EA2), Broadband® (91.7 % mortality) gave significantly (p < 0.05) higher mortality of BFW adults, compared to EcoBb® (65 % mortality), Meta 69 (59.5 % mortality) and M. anisopliae isolate EA2 (64.2 % mortality), which did not differ significantly from one another. In a sand bioassay, Broadband® (85 % mortality) resulted in significantly (p < 0.05) higher mortality of BFW larvae compared to Eco-Bb® (55 % mortality) and Meta 69 (70 % mortality). The results indicated that all the EPF isolates tested were effective against juvenile and adults stages of the BFW, with Broadband® showing the most promise in controlling the BFW under laboratory conditions. The last objective of the study was to evaluate the combined use of the EPF; Eco-Bb®, Broadband®, Meta 69 and a local isolate M. anisopliae EA2, with the EPN, S. yirgalemense against BFW larvae and adults. The EPF were either applied alone, or at the same time as S. yirgalemense, or S. yirgalemense was introduced 1 and 2 weeks after fungal application; the EPNs were also applied alone. Results showed that 100% larval and adult mortality was obtained when S. yirgalemense was applied 1 or 2 weeks after Eco-Bb® and BroadBand® application. Synergistic interactions were noted when Eco-Bb® and S. yirgalemense, BroadBand® and S. yirgalemense, Meta 69 and S. yirgalemense, and M. anisopliae isolate EA2 and S. yirgalemense when applied 1 or 2 weeks after application of the EPF. Additive interactions were observed when the EPF and S. yirgalemense were applied simultaneously. Future research into the biological control of the BFW, using EPNs and EPF, should be focused on conducting large-scale field trials to demonstrate their potential use as biocontrol agents, within an integrated pest management programme. Both entomopathogens have shown outstanding potential to control the BFW when used alone, and in combination, could provide an economically viable control strategy against the BFW.
The biology and management of aerial populations of woolly apple aphid, Eriosoma lanigerum (Hausmann) (Homoptera: aphididae)
(Stellenbosch : Stellenbosch University, 2001-03) Heunis, J. M. (Juanita Maria); Pringle, K. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The basic biology of Eriosoma lanigerum (Hausmann) and its natural enemy, Aphelinus mali (Haldeman), was investigated in the Western Cape Province of South Africa. The first instar nymph can be identified by the absence of cornicles and the adult female by the presence of the vulva. Body length and distance between cornicles can be used to distinguish between the 2nd , 3rd and 4th instars. The development of E. lanigerum was negatively influenced by temperatures above 27DC. The net replacement rate (Ro) and intrinsic rate of increase (rm) peaked at 20DC. The theoretical lower and upper threshold temperatures for development were estimated at 4.48DC and 28.07DC, respectively. Crawlers of E. lanigerum migrated from the roots up into the trees during spnng to start new infestations. Colonies became visible from December and maximum colony numbers were reached from the end of summer until autumn, at which time most of the colonies were parasitised by A. mali. Colony numbers declined at the end of autumn after high parasitism and the appearance of winged E. lanigerum. The aphid overwintered on the tree. Chemical sprays, rain during spring and high temperature influenced population numbers negatively. E. lanigerum can be monitored by counting the unparasitised colonies in leaf axils of half of each of 25 trees per 2 hectare plot with 5 unparasitised colonies as the economic threshold. Sampling error was high at 40% but increasing the number of trees did not reduce it. Presence-absence sampling, which will reduce the time required for monitoring, did not seriously compromise the reliability of decisions regarding the necessity for intervention. Chemicals containing nitrogen usually sprayed for bitterpit control stimulated the settling of E. lanigerum crawlers on Granny Smith trees, while fruit weevil barriers for the control of Phlyctinus callos us Boh. limited crawler movement into the trees but did not prevent colonisation. All the postembryonic developmental stages of E. lanigerum were parasitised by A. mali. Complete parasitism of the population was never reached as younger instars sheltered under other aphids and mummified aphids. Development of A. mali was not influenced negatively by high temperatures. The minimum developmental temperature and number of degree days needed for development of the larval stage and emergence of the adult from the mummy were .6.72°C and 172.41°D, and 10.27°C and 109.89°D respectively. Mummies collected during early winter survived long periods of cold storage in postdiapause. The rrummum threshold temperature for postdiapause development of A. mali was ·10.15°C. Most chemicals tested against A. mali adults were highly toxic to the wasp, except endosulfan and two growth regulators, flufenoxuron and fenoxycarb. The mortality of adults exposed to the fungicides tested was low within the first 24 hours. The percentage emergence from the mummies was high for all chemicals tested, but more than 60% of the adults died soon after emergence from mummies treated with chlorpyrifos. Nearly 30% of the adults died soon after they emerged from carbaryl (XLR-Plus) and fenthion treated mummies. The growth regulators, flufenoxuron and fenoxycarb, did not influence fecundity adversely.
Biology of subterranean populations of woolly apple aphid, Eriosoma lanigerum (Hausmann)(Homoptera:Aphididae), in apple orchards
(Stellenbosch : Stellenbosch University, 2000-03) Damavandian, M. R.; Pringle, K. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: A study was made of the basic biology of subterranean Eriosoma lanigerum (Hausmann) populations in apple orchards in the Western Cape Province of South Africa. The absence of cornicles and the presence of a vulva could be used to identify 1st instar nymphs and adults respectively. Body length, body width and length of the hind femur are useful for separating 2nd , 3rd and 4th instars. However, separation of 2nd from 3rd instar nymphs was very unreliable. Maximum population growth rate was at 23°C while at 30 °C population growth was zero. The estimated minimum and maximum threshold temperatures for development were 4.32 and more than 30°C respectively. Numbers of underground E. lanigerum in soil samples taken using mechanical and hand augers were similar. However, numbers of aphids in samples were influenced by the distance from the trunk at which the samples were taken and the presence and the type of root material in the samples. More aphids were recorded close to the trunk, and at a given distance from the trunk more aphids were recorded if there was root material in the sample, especially if the roots were galled. early autumn (February, March) and declined during winter, especially if the winter rainfall was high. These cycles coincided with the nitrogen cycles in the roots. Embryos were also present in all instars throughout the year. There were more embryos in the 4th instar and adult aphids than in the other instars. The highest number of embryos in the 4th instar and adult aphids occurred during spring, which coincided with peak nitrogen levels in the roots of apple trees. Nitrogen levels in root material adjacent to galls and in ungalled roots were higher than in root galls. A number of entomopathogenic fungi, including species of Conidiobolus, Hirsufella and Beauveria were found. Their present contribution to biological control is not known. A straw mulch suppressed subterranean E. lanigerum population levels at least as well as the soil insecticide, imidacloprid, currently in use.
Biology, ecology and management of white wax scale, Ceroplastes destructor Newstead (Hemiptera: Coccidae), on citrus and syzygium
(Stellenbosch : Stellenbosch University, 2000-12) Wakgari, Waktola (Waktola Muleta); Giliomee, J. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The population density of the white wax scale, Ceroplastes destructor Newstead, has increased since 1994 in certain areas of Western and parts of Eastern Cape Provinces of South Africa where citrus is grown, particularly on Citrus reticulata (Blanco). A study was conducted to investigate its morphology, biology and ecology as contributions to the development of a sound integrated management programme. Characteristics of the immature stages and adult females were described and illustrated from field-collected and slide-mounted specimens. A key to the different stages and morphometeric characteristics useful for separating them are provided. No significant differences in female fecundity were found between orchards (P > 0.05). However, fecundity varied significantly between female size classes from the same orchard (P < 0.001). Female body-size also differed significantly between orchards (P < 0.05) and was significantly positively correlated with fecundity (P < 0.01). C. destructor has one discrete generation per year in South Africa. Oviposition commenced in November and continued through to the end of December with a few females ovipositing until mid January. Population density of the second instar peaked in February while the third instar extended from March to the end of July, followed by a peak population of adults in August. Seven primary and three secondary parasitoids, as well as four predator species attacking C. destructor were identified. Aprostocetus (= Tetrastichus) ceroplastae (Girault) was the dominant species, accounting for 78.87% of the total primary parasitoids reared. Peak numbers of parasitoids and predators were synchronized with peak emergence of susceptible scale stages, indicating that the host-parasitoid/predator system contained a density-dependent regulatory mechanism. Key mortality factors varied slightly between two of the orchards. Key stage mortality determined from a cohort life table was generally in the third instar (LIlI) and preovipositional female (POF) stage. Significant density-dependent mortality factors were demonstrated for the first instar (LI) and PDF stage. Dispersal of C. destructor is by first instar nymphs and the numbers caught on a series of yellow sticky traps varied significantly between crawler densities at the source, trap distances and trap directions from the source (P < 0.001). The numbers caught were positively correlated to the initial crawler density at the source (P < 0.01), suggesting that dispersal was density dependent. Trap distance and the numbers caught were inversely correlated (P < 0.01). Evaluation of effects of different densities of C. destructor on growth, survivorship and reproduction of scales as well as on leaf bearing ability of trees and area of leaf surface covered with sooty mould fungus was carried out on naturally infested Syzygium (= Eugenia) malaccensis (L.) plants. Scale body size and fecundity were inversely related to scale density (P < 0.01), suggesting density-dependent intraspecific competition. Scale survivorship generally declined with increasing density whereas scale parasitism and predation were positively correlated with density (P < 0.05). At high scale densities production of new leaves was significantly reduced (P < 0.01), reducing the resource base for subsequent generations of scale. Scale density and leaf area covered with sooty mould fungus were significantly positively correlated (P < 0.05). The toxicity of four synthetic insecticides against the three immature stages of C. destructor and of eight insecticides against the parasitoid A. ceroplastae was evaluated. Development of the first and second instars of C. destructor was completely arrested by the chemicals. Female fecundity, fertility and body sizes of survivors of treatments applied at the LIII stage were not significantly affected by any of the chemicals (P > 0.05). All the chemicals exhibited high toxicity to A. ceroplastae and hence are not recommended for integrated management of C. destructor in citrus orchards where A. ceroplastae plays an important role.
Bionomics, behaviour and control of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), in pome fruit orchards in South Africa
(Stellenbosch : Stellenbosch University, 2003-03) Blomefield, Thomas Loftus; Giliomee, J. H.; Pringle, K. L.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The codling moth, Cydia pomonella (L.) has been a major pest of pome fruits since before the turn of the last century. However, despite its high economic profile little is known about the bionomics and . behaviour of this pest in apple orchards in South Africa, information required for the development of a sustainable integrated management programme. In field trials there was contingency between the time of year and the upper and lower half of the tree. First generation moths laid significantly more eggs in the bottom half of the tree while second and third generation moths laid significantly more eggs in the top half of the tree. The preferred oviposition sites on Granny Smith (GS) and Golden Delicious (GD) cultivars, in order of preference, were leaves, fruit and wood. More eggs were laid on the fruit ofGS spurs (35.6 %) than on those ofGD spurs (10.7 %). On fruit spurs there was a significant increase in the number of eggs on GD leaves and GS fruit over the season, whereas the number of eggs on GS leaves and GD fruit remained constant. On branches there was an increase in the number of eggs on GD and GS leaves, but not on the fruit or wood. The preferred oviposition site on the fruit was the fovea of the stalk insertion and the rounded cheek area surrounding the fovea. The distribution within different fruit bearing classes (1 - 4 fruit per spur) was random only for one fruit per spur, while on the other spur classes clustering occurred. In laboratory studies of the embryonic and immature stages there was a linear relationship between rate of development and constant temperatures of 15, 17,20,25 and 30·C ± l·C. The lower threshold temperatures for embryonic, larval and pupal development were 11.1, 7.9, 9.9°C respectively. The degree-days required to complete embryonic, larval and pupal development were 80.5, 345, and 279 respectively. The response of the different stages to constant temperatures was similar to that under fluctuating temperatures. At temperatures below 16°C or abouve 27°C moths did not mate and few eggs were laid. Moth longevity decreased with increasing temperature. There was seasonal variation in longevity and oviposition at constant and fluctuating temperatures. Summer adults produced significantly more eggs than spring adults at constant temperatures. At a constant temperature of2S·C and fluctuating temperatures there were five distinct larval instars. The similarity between the mean head capsule width and ranges for each instar reared on fruit of different stages of development at fluctuating temperatures indicates that fruit development and temperature have little influence on mean head capsule width. From sleeve-cage studies in the orchard there was no significant difference in the fecundity of spring and summer moths. In the beginning of October spring moths produced significantly fewer eggs than in November. Egg mortality increased from 8.2 %in spring to 21.2 %in summer. Failure of 1st instar larvae to penetrate the fruit ranged from 4.9 % to 19.5 %, while mortality oflarvae from egg hatch to emergence from the fruit ranged from 29.7 % to 42.9 %. Mortality of 5th instar larvae after emerging from the apples ranged from 0 % to 8.7 % and pupal mortality from 0 % to 3.5 %. On large 27-year old trees more overwintering larvaewere found on Golden Delicious (13.9) than on Granny Smith trees (5.7), with over 70 % oflarvae being found in pruning wounds on both cultivars. On small 7-year old Golden Delicious and Granny Smith trees the mean number oflarvae was 0.5 and 2.0 per tree. A combined mating disruption and insecticide control programme reduced codling moth resistant populations to levels requiring a minimum to no insecticide intervention for several seasons. The efficacy of a pheromone based strategy, number of pheromone treatments, number of dispenserslha and level of insecticide intervention required are strongly influenced by prevailing weather conditions. Fruit infestation in orchards under a mating disruption programme and under an insecticide programme were greater along the borders compared to the interior. The presence of horticultural mineral oil on the leaves and branches did not have a detrimental effect on oviposition nor was there any significant ovicidal effect. A significant ovicidal effect was obtained when applied after oviposition. In field trials, insecticides with lower levels of efficacy than the primary insecticide, azinphos-methyl, provided acceptable control when successfully incorporated into a spray programme which followed a policy of alternation of insecticides across generations. The least variation in the number of degree-days between biofix and first egg hatch of the spring flight was when the second trap catch (Biofix 2) was used as the biofix. A biofix based on the first evening when the temperature reached or exceeded 1TC at 18:00 after first trap catch also showed less variation than when the biofix was based on first trap catch. The mean number of degree-days accumulated between Biofix 2 and first egg hatch was found to be 139.1 ° D. The number of degreedays between the first and second flight biofixes varied between 531.2 and 488.87°D with a mean of 508.1°D.
'n Bydrae tot die biologie en beheer van die valskodlingmot Cryptophlebia leucotreta (Meyr.) (Lepidoptera : Eucosmidae) op nawels
(Stellenbosch : Stellenbosch University, 1981-12) Schwartz, A. (Allen); Giliomee, J. H.; Stellenbosch University. Faculty of AgricSciences. Dept. of Conservation Ecology and Entomology.
EKSERP: Vanwee die voortdurende probleme wat die valskodlingmot, Cryptoph lebia leucotreta (Meyr.), by die verbouing van nawels in die Oos-Transvaalse Laeveld daarstel, is 'n indringende studie van hierdie insekprobleem onderneem. Die biologie van die insek is onder sowel laboratorium as natuurlike toestande nagevors. Daar is bevind dat temperatuur 'n belangrike rol in die ontwikkeling van die insek speel. By 20 tot 30°C het temperatuurstygings die ontwikkeling van die insek laat versnel. By 35°C het die lewensduur van die volwasse motte afgeneem en is geen eiers gelê nie . Die valskodlingmot is deur middle van 'n kunsmatige metode geteel om genoegsame proefmateriaal te verkry. Verskeie verbeteringe is in die bestaande tegniek aangebring.
Carcinops pumilio (Erichson) (Coleoptera: Histeridae) as a predator of house flies in poultry manure
(Stellenbosch : Stellenbosch University, 2004-04) Achiano, K. A. (Kwaku Akoming); Giliomee, J. H.; Stellenbosch University. Faculty of Agricultural and Forestry Sciences. Dept. of Entomology and Nematology
ENGLISH ABSTRACT: In surveys carried out on poultry farms in the Western Cape Province, South Africa, the larvae of the flies Musca domestica L., Fannia canicularis (L.) and Leptocera sp. were found to be numerous. The majority of M domestica larvae and the mite Proctolaelaps sp. were recovered from manure with temperatures between 20 and 26°C while the larvae of F. canicularis and Leptocera sp. were mostly found between 14 and 22°C. Predominant predatory arthropods in the manure were the histerid Carcinops pumilio (Erichson), the staphylinid Philonthus sordidus (Gravenhorst) and the mite Macrocheles muscaedomesticae (Scopoli). These had a manure temperature tolerance of between 12 and 31°C. Macrocheles muscaedomesticae and P. sordidus preferred fresh manure, whilst C pumilio preferred aged manure. Therefore these two predators could complement one another in integrated pest management programmes. From a study of the vertical cross-sectional profile of the manure cone it was clear that the larvae of the prey species M domestica and F. canicularis and predator P. sordidus distinctly occupy the crest of the manure cone. The succession of arthropods in accumulating poultry manure and the effect of manure height on their numbers was studied. The prey species M domestica and F. canicularis were the first colonizers followed by the predators P. sordidus and M muscaedomesticae. Carcinops pumilio was a late colonizer. The numbers of M domestica and F. canicularis larvae were negatively correlated with the increase in manure height whilst the numbers of the predators C pumilio and M muscaedomesticae were positively correlated with this. The total developmental time of C pumilio from egg to adult emergence at 30°C was 20.5 days. Two larval instars were recorded. The immature stages sustained about 50% mortality before adult emergence. Carcinops pumilio adults can live up to 130 days at 30°C and had a Type I survivorship curve. The intrinsic rate of natural increase (rm) was 0.064943 and net reproduction rate (Rs) was 20.191.The rate of oviposition was directly proportional to body size and weight. Increase in density had a dampening effect on fecundity and led to an increase in developmental time. Thus density will be a critical factor in any mass rearing programme for this predator of fly larvae. In addition, an increase in density stimulated the dispersal of C. pumilio. A crowding level of 50 C. pumilio adults per 200ml container resulted in the least dispersal which did not exceed 2.5% per day, compared with up to 24.0% at a crowding level of 400. The predation rate of flies by C. pumilio in the laboratory decreased with an increase in predator density, but increased with an increase in starvation. Starvation had no effect on predation rate of M muscaedomesticae. A technique exploiting Drosophila melanogaster Meig. as a source of prey was successfully developed for rearing C. pumilio, which could be of commercial value. Drosophila melanogaster appeared to be an ideal candidate as a source of prey for mass rearing C. pumilio due to its short developmental time of about ten days. It is also inexpensive and easy to breed, and has a very high biotic potential. Carcinops pumilio that were fed on artificial diet had a prolonged developmental time and increase in weight, and laid fewer eggs than those fed on natural diet. C. pumilio completed its development on the artificial diet and both the F, and F2 generations fed on an artificial diet were able to lay eggs. This could be the first step towards finding an artificial diet that would allow continuous rearing of C. pumilio and their availability at all times for utilization in the biological control of houseflies.
Changes in the Berg River Basin over time
(Stellenbosch : Stellenbosch University, 2018-12) Magoba, Rozwivhona Faith; Esler, Karen J.; Brown, Cate; Mazvimavi, Dominic; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
ENGLISH ABSTRACT: The nature of river ecosystems is influenced by the history of activities in their basins. This dissertation investigated historic changes in the Berg River Basin and their influence on river ecosystem structure. The central assumption was that all activities in a river basin landscape contribute either directly or indirectly to the condition (physical, biological, chemical) of rivers that run through them. It was first necessary to establish what changes had taken place in the river basin over time and this was done in different ways at different spatial scales. Changes in land-use were collated and mapped across the basin since these were considered to influence the river’s flow regime and river channel structure. Predictions were made about how changes in flow and river channel habitat would influence the distribution and abundance of aquatic macroinvertebrates. A history of land-use changes over the Berg River Basin was explored between four periods, 1955-1965, 1976-1985, 1996-2005 and 2006-2015. The bulk of the dryland crop production was in the lower foothills and lowlands while the upper foothills comprised orchards, vineyards and forestry. From 1955-2015 the extent of agricultural land in the basin declined by half as dryland crops were changed to orchards and vineyards and large tracts of land were left fallow. Over the same period the area under forest declined by 73% and urban areas doubled in size as did the number of farm dams in response to the increased need for irrigation to supply the more water hungry crops. The effects of the changes in land-use, the increase in farm dams and the construction of large dams on the river’s flow regime was investigated next. Changes in flow were explored at four river gauges along the length of the Berg River up- and down-stream of the two main in channel dams; the Berg River Dam in the Upper Foothills and Misverstand Dam in the Lowlands. In general the changes were more marked at the downstream gauges and the trends were towards increased dry season flows and slightly decreased wet season flows due to release of water from, and capturing of floods by the in-channel dams to meet irrigation demand in the dry season. Flow pattern from early records was better correlated with rainfall than that from the recent record indicating that flow changes were likely to be attributable to anthropogenic effects such as land-use and water resource developments. Both land-use and water resource developments were predicted to have consequences on river channel shape and habitat that was investigated next. Changes in river channel shape, the extent and composition of the floodplain and riparian area was mapped from aerial photographs at five sites along the Berg River and at five adjacent tributaries. Each site responded differently, which was not unexpected, and reductions in the extent of the channel and riparian area were more severe along the Berg River main stem when compared to the tributaries. Along tributaries no floodplains were discernible at the scale measured, however a decreased in extent over time along the main river except downstream of the Berg River Dam where the floodplain area had increased due to the previously braided channel of 1938 changing to a single thread channel with floodplain and a greater area of sandbanks. Changes in river habitat, such as these, were predicted to effect change in the abundance and community structure of aquatic macroinvertebrates, which was investigated next. The abundance of aquatic macroinvertebrates was studied from the 1950s to 2015 and showed a reduction in simulids and baetids with an increase in the abundance of chironomids, indicating a decline in water quality. Changes in other groups indicated a decline in quality of habitat, for instance a loss of plecopterans that prefer clean gravel beds being replaced by caenids that prefer a sandy channel bottom. In 2015 there were also more groups of invertebrates that are associated with slow-flowing areas and marginal vegetation, which was presumed to have occurred in response to the clearing of woody alien trees from the river banks and the subsequent proliferation of aquatic and marginal plants along the water’s edge. Data collected for land-use, hydrology, channel and riparian changes, macroinvertebrates were synthesized using BEST (BIOENV and BVSTEP) multivariate statistics in PRIMER to search for high rank correlations between environmental and biological variables. When the environmental variables were tested against the biological variables showed that changes in macroinvertebrates were strongly related to area of plantations, area of undeveloped land, the extent of braiding, maximum 5-day average discharge in the wet season and the daily average volume in the dry season. Environmental variables were most influenced/driven by location (separated into sub-basins) while time was the driving factor for the macroinvertebrates data.

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