Browsing by Author "Esterhuizen, Nanike"

Now showing 1 - 4 of 4
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    The botanical origin, physicochemical properties and antibacterial activity of selected West Coast honeys
    (Stellenbosch : Stellenbosch University, 2020-04) Esterhuizen, Nanike; Wossler, Theresa Clair; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Honey is a complex natural product made by honey bees. In recent years consumer preference in the market has shifted towards honeys with distinct characteristics such as unique floral origin (i.e. monoflorals) and potential health benefits. The specific physical and chemical properties that make every honey unique are primarily influenced by the distinct nectar composition of the plants that were visited by the bees. The Cape Floristic Region (CFR) is characterised by high plant species diversity and exceptionally high species endemism. With the close association between botanical origin and honey properties in mind, this study aimed to identify novel honeys produced from fynbos plants along the West Coast of South Africa that could be marketed as an exclusive, niche product to higher tier local and international consumers. The botanical composition of honeys was investigated by generating the first pollen library for the West Coast and using melissopalynology to identify honey floral components and monofloral varieties. Honey bees preferred and utilised similar floral sources across space and time, with differences in botanical origin between years ascribed to differences in floral availability, due to changes in rainfall. Sandbos (Aspalathus spinescens form A) was the most abundant monofloral honey produced. The physicochemical composition of honey also varied over space and time, as well as with honey age. However, the majority of honeys produced along the West Coast were of good quality and complied with local as well as international regulations – fresh and after 12-months in storage. Hydrogen peroxide was responsible for the antibacterial activity of the West Coast honeys, which was confirmed using a phenol equivalence agar well diffusion assay. Almost 70% of honeys were potentially therapeutically useful, although the variation in antibacterial activity of specific monofloral honey varieties was quite high. Unfortunately, the sample sizes of different honey varieties were limited due to the severe drought conditions experienced between 2015 and 2017, making it difficult to give definitive recommendations on honey properties to be used for value-added marketing. Climate change scenarios predict that the West Coast will become warmer and drier in the future and environmental fluctuations such as changes in rainfall and temperature that affect nectar availability will also greatly influence honey production. The beekeeping industry should focus on optimising the honey yield from drought-tolerant plant species such as sandbos, through the identification and preservation of sites where these plants occur, or through cultivation. This approach of botanical, physicochemical and antibacterial characterisation of honeys produced from indigenous flora could be extended over larger areas of the CFR with the help of beekeepers and citizen science initiatives. Research characterising the unique honeys produced from indigenous vegetation must continue, increasing honey’s value on local as well as international honey markets and in turn boosting the beekeeping industry of South Africa.
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    Effects of thermal history on temperature-dependent flight performance in insects : Ceratitis capitata (Diptera: Tephritidae) as a model organism
    (Stellenbosch : Stellenbosch University, 2013-12) Esterhuizen, Nanike; Terblanche, J. S.; Clusella-Trullas, Susana; Van Daalen, Corne E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Understanding the impact of environmental factors on locomotor performance and flight energetics is of fundamental importance to understanding evolution and ecology. Increased performance that leads to increased dispersal ability can result in increased migration distance to reach optimal habitats, increased gene flow between populations and an overall contribution to the survival of individuals as well as the structuring of species‟ geographic range sizes. The temperature-dependent nature of insects, in conjunction with predicted climate change and shifting optimal climatic ranges, could have important ecological and economic consequences such as increased invasion by alien and pest species. In this study, the influence of thermal history on temperature-dependent flight performance was investigated in a notorious invasive agricultural pest, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at random at either of those temperatures (Ttest) as adults in a full-factorial experimental design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Performance increased with increasing Ttest across all acclimation groups, e.g. at 15°C only 10% of all flies had successful flight, whereas at 30°C the success rate was 76.5%. Even though Tacc alone did not affect flight performance, it did have an effect in combination with Ttest. The negative interaction term Ttest x Tacc, in combination with a multiple comparison between Tacc groups at each Ttest, indicated that flies acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures. This provides partial support for the "colder is better‟ hypothesis. To explain these results, several key, flight-related traits were examined to determine if Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase (CCO) activity. Although significant effects of Tacc could be detected in several of the traits examined, with emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any one of these traits. To illustrate the potential applied value of this study, the main flight performance outcomes were also coupled with a degree-day (thermal development) model to determine if knowledge of flight ability could improve predicted population dynamics. The results and insights obtained from this study are broadly applicable to a variety of insect species and demonstrate that, by recognising the impact of environmental factors on locomotor performance and flight energetics, an increased understanding of the functioning, biology and evolution of flight-capable arthropods can be obtained.
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    Effects of within-generation thermal history on the flight performance of Ceratitis capitata : colder is better
    (The Company of Biologists, 2014-07) Esterhuizen, Nanike; Clusella-Trullas, Susana; Van Daalen, Corne E.; Schoombie, Ruben E.; Boardman, Leigh; Terblanche, John S.
    The influence of thermal history on temperature-dependent flight performance was investigated in an invasive agricultural pest insect, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at these temperatures (Ttest) as adults using a full-factorial study design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Successful flight performance increased with increasing Ttest across all acclimation groups (from 10% at 15°C to 77% at 30°C). Although Tacc did not affect flight performance independently, it did have a significant interaction effect with Ttest. Multiple comparisons showed that flies which had been acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures, but warm-acclimated flies did not outperform cold-acclimated flies at warmer temperatures. This provides partial support for the ‘colder is better’ hypothesis. To explain these results, several flight-related traits were examined to determine whether Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase enzyme activity. Although significant effects of Tacc could be detected in several of the traits examined, with an emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any of these traits. Overall, these results are important for understanding dispersal physiology despite the fact that the mechanisms of acclimation-related changes in flight performance remain unresolved.
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    The metabolic costs of sexual signalling in the chirping katydid Plangia graminea (Serville) (Orthoptera: Tettigoniidae) are context dependent : cumulative costs add up fast
    (The Company of Biologists, 2017) Doubell, Marcee; Grant, Paul B. C.; Esterhuizen, Nanike; Bazelet, Corinna S.; Addison, Pia; Terblanche, John S.
    Katydids produce acoustic signals via stridulation, which they use to attract conspecific females for mating. However, direct estimates of the metabolic costs of calling to date have produced diverse cost estimates and are limited to only a handful of insect species. Therefore, in this study, we investigated the metabolic cost of calling in an unstudied sub-Saharan katydid, Plangia graminea. Using wild-caught animals, we measured katydid metabolic rate using standard flow-through respirometry while simultaneously recording the number of calls produced. Overall, the metabolic rate during calling in P. graminea males was 60% higher than the resting metabolic rate (0.443±0.056 versus 0.279±0.028 ml CO₂ h⁻ ¹ g⁻ ¹), although this was highly variable among individuals. Although individual call costs were relatively inexpensive (ranging from 0.02 to 5.4% increase in metabolic rate per call), the individuals with cheaper calls called more often and for longer than those with expensive calls, resulting in the former group having significantly greater cumulative costs over a standard amount of time (9.5 h). However, the metabolic costs of calling are context dependent because the amount of time spent calling greatly influenced these costs in our trials. A power law function described this relationship between cumulative cost (y) and percentage increase per call (x) (y=130.21x⁻¹˙⁰⁶⁸, R2=0.858). The choice of metric employed for estimating energy costs (i.e. how costs are expressed) also affects the outcome and any interpretation of costs of sexual signalling. For example, the absolute, relative and cumulative metabolic costs of calling yielded strongly divergent estimates, and any fitness implications depend on the organism's energy budget and the potential trade-offs in allocation of resources that are made as a direct consequence of increased calling effort.