Thermal performance curves (TPCs), which quantify how an ectotherm's body temperature (T b ) affects its performance or fitness, are often used in an attempt to predict organismal responses to climate change. Here, we examine the key -but often biologically unreasonable -assumptions underlying this approach; for example, that physiology and thermal regimes are invariant over ontogeny, space and time, and also that TPCs are independent of previously experienced T b. We show how a critical consideration of these assumptions can lead to biologically useful hypotheses and experimental designs. For example, rather than assuming that TPCs are fixed during ontogeny, one can measure TPCs for each major life stage and incorporate these into stage-specific ecological models to reveal the life stage most likely to be vulnerable to climate change. Our overall goal is to explicitly examine the assumptions underlying the integration of TPCs with T b , to develop a framework within which empiricists can place their work within these limitations, and to facilitate the application of thermal physiology to understanding the biological implications of climate change.

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The ability of insects to cope with stressful temperatures through adaptive plasticity has allowed them to thrive under a wide range of thermal conditions. Developmental plasticity is generally considered to be a non-reversible phenotypic change, e.g. in morphological traits, while adult acclimation responses are often considered to be reversible physiological responses. However, physiologically mediated thermal acclimation might not follow this general prediction. We investigated the magnitude and rate of reversibility of developmental thermal plasticity responses in heat and cold tolerance of adult flies, using a full factorial design with two developmental and two adult temperatures (15 and 25°C). We show that cold tolerance attained during development is readily adjusted to the prevailing conditions during adult acclimation, with a symmetric rate of decrease or increase. In contrast, heat tolerance is only partly reversible during acclimation and is thus constrained by the temperature during development. The effect of adult acclimation on heat tolerance was asymmetrical, with a general loss of heat tolerance with age. Surprisingly, the decline in adult heat tolerance at 25°C was decelerated in flies developed at low temperatures. This result was supported by correlated responses in two senescenceassociated traits and in accordance with a lower rate of ageing after low temperature development, suggesting that physiological age is not reset at eclosion. The results have profound ecological consequences for populations, as optimal developmental temperatures will be dependent on the thermal conditions faced in the adult stage and the age at which they occur.

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Tuta absoluta Meyrick (Lepidoptera: Gelechiidae), commonly known as the tomato borer, is native to South America and has rapidly spread in various European countries becoming one of the major threats of tomato crop. The parasitic wasp Trichogramma achaeae Nagaraja and Nagarkatti (Hymenoptera: Trichogrammatidae) has been suggested as a possible biological control agent of the invasive pest and several aspects of its taxonomy have been elucidated. As for other egg parasitoids, the parasitism rate of this species is influenced by the rearing host and by the biotic environment, especially temperature. Starting from commercially available material, we assessed the influence of different rearing host eggs on T. achaeae longevity and fertility. We found that a single generation of the parasitoid on Tuta absoluta eggs laid on tomato leaf significantly improved T. achaeae attack rate against the tomato borer.Moreover, we found a positive effect between temperatures during development (acclimation) and the fertility of the parasitoid at different temperatures. This was particularly evident at 15°C which was optimal for parasitoid fertility at low temperatures. We conclude that the combination of rearing system (plant ? host egg) and temperatures (during development and use) are crucial factors for optimizing efficiency in terms of longevity and fertility of this species as a biocontrol agent of the tomato borer.