Masters Degrees (Conservation Ecology and Entomology)

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Browsing Masters Degrees (Conservation Ecology and Entomology) by browse.metadata.advisor "Boardman, Leigh"

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    Impacts of temperature variation on performance, life-history and flight ability of the false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae)
    (Stellenbosch : Stellenbosch University, 2018-12) Boersma, Nevill; Terblanche, J. S.; Boardman, Leigh; Gilbert, Martin; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: The sterile insect technique (SIT), the process of mass-rearing, sterilizing and releasing sterile insects, can be used to can be used to combat economically important pests by supressing their population numbers as part of an integrated pest management programme. The success of SIT programmes depends upon the production of high-quality, competitive insects for field release. In SIT programmes, the influence of temperature variation during larval development and chilling during storage and their effects on the field performance of adult mass-reared insects are poorly understood but may be a significant avenue for increasing programme efficacy. The use of different temperatures to rear, handle and immobilise insects allows increased quantities of insects to be collected, handled, irradiated, transported and released. Unfortunately, the use of different temperature regimes in the rearing, storage, handling and shipping of insects have poorly understood impacts on the field performance of mass-reared insects. I mainly studied the impact of different developmental temperatures on larvae and treatment temperatures on adults, examining adult performance in the false codling moth Thaumatotibia leucotreta (Meyrick). After larvae were reared at 15, 20 or 25 °C for their full developmental period, the effect of different acute (2 h) temperature treatments (10, 15 or 20 °C) during the adult stage on traits of (i) cold tolerance, (ii) fecundity and (iii) longevity were determined. In addition, I assessed the flight performance of adults in both laboratory and field conditions after they were exposed to chilling (2 °C) for 16 h during the adult stage. The cold tolerance of adults was not influenced by larval acclimation temperature but was affected by sex and adult treatment temperature. Adult fecundity and longevity were affected by larval acclimation temperature, adult treatment temperature and the interaction of these factors with sex. In flight assays, adults exposed to 2 °C for 16 h performed better in colder environments, both in the laboratory and the field, than adults not subjected to pre-release cold treatment. The benefits of chilling for improved field recapture rates, however, depended on the specific ambient temperature upon release. These results suggest a complex, and in some cases sexdependent, interplay of short- and longer-term temperature history across developmental stages for these traits. Further studies of how these and other traits might respond to artificial manipulation, coupled with information on how any induced trait variation impacts field performance, are essential for the SIT and pest management, with far-reaching implications for understanding thermal adaptation of ectotherms
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    Thermal limits of activity and survival in false codling moth, Thaumatotibia leucotreta (Lepidoptera: Tortricidae) : life-stage and ramping rate effects
    (Stellenbosch : Stellenbosch University, 2014-12) Uys, Wilmari; Terblanche, J. S.; Mitchell, Katherine A.; Boardman, Leigh; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: Knowledge of the factors affecting thermal limits of insects are of central importance to developing control, risk assessments and post-harvest pest management strategies. To better understand these limits, this study investigated life-stage-related variation in acute critical thermal limits to activity and lethal limits in larvae and adults of the false codling moth, Thaumatotibia leucotreta. The effects of variation in rates of cooling and heating on lower and upper critical thermal limits in both life-stages were also examined. I specifically tested the prediction, generated from dynamic ramping assays, that life-stages with a strong positive association between thermal tolerance estimates and ramping rate are predicted to show less pronounced hardening (acute plasticity) effects. T. leucotreta larvae generally survive at more extreme temperatures than adults, while adults can maintain activity over a broader thermal range; mean CTmin larvae vs adults: 10.5 °C vs. 2.3 °C; CTmax: 42.5 °C vs 42.4 °C (at 0.06 °C/min rates of temperature change); mean survival probability for 50 % of the population for 2 h exposure; LLT50 larvae vs adults: -12.0 °C vs -8 °C; ULT50 larvae vs adults: 49.2 °C vs 41.2 °C. In addition, larvae show a more pronounced negative effect of cooling rate on critical thermal minima (CTmin) and a stronger positive effect of heating rate on critical thermal maxima (CTmax) than adults, suggesting that adults are likely to be more thermally plastic. An independent test of this prediction supports the idea that T. leucotreta adults have a pronounced heat-hardening response, which likely facilitates their elevated CTmax under slower heating rates in dynamic assays. By contrast, larvae have less pronounced heat hardening responses (although higher basal tolerance), supporting the limited plasticity inferred from ramping rate variation in CTmax trials. Life-stage-related variation in thermal limits also varied depending on the choice of cooling/heating rate (some differences at one rate disappeared and vice versa). Life-stage-related variation in basal and plastic thermal tolerance further suggests there is a trade-off between these, even within a species. This suggests that hardening effects, and their variation among life-stages, could play a role in predicting the impact of heating rate variation under natural conditions. The results of this study are significant to understanding this species’ physiology and how field temperature variation may impact population dynamics.