Browsing by Author "Uys, Wilmari"

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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.