Thermal limits to survival and activity in two life stages of false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae).
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The present study examines life stage-related variation in the thermal limits to activity and survival in an African pest, the false codling moth Thaumatotibia leucotreta (Lepidoptera, Tortricidae). Thermal tolerance, including the functional activity limits of critical thermal maxima and minima (CTmax and CTmin respectively), upper and lower lethal temperature, and the effect of heat and cold hardening (short-term acute plasticity), is measured across a diverse range of low or high temperature stress conditions in both larvae and adults. We also report the sum of inducible and cognate forms of the amounts of heat shock protein 70 (HSP70) as an explanatory variable for changes in thermotolerance. The results show that the larvae have high variability in CTmax and CTmin at different ramping rates and low levels of basal (innate) thermal tolerance. By contrast, the adults show high basal tolerance and overall lower variability in CTmax and CTmin, indicating lower levels of phenotypic plasticity in thermotolerance. HSP70 responses, although variable, do not reflect these tolerance or survival patterns. Larvae survive across a broader range of temperatures, whereas adults remain active across a broader range of temperatures. Life stage-related variation in thermal tolerance is most pronounced under the slowest (most ecologically-relevant) ramping rate (0.06 ∘Cmin–1) during lower critical thermal limit experiments and least pronounced during upper thermal limit experiments. Thus, the ramping rate can hinder or enhance the detection of stage-related variation in thermal limits to activity and survival of insects.