Insect pest development is often linearly related to air temperature, without taking into account the multiple interactions between the particular host plant and pest, the microclimatic conditions actually experienced by the insect, and the non-linear response of insect development rate to temperature. In this study, using an integrative biophysical model, we have investigated effects of both climatic and tree structure changes on the development of a phytophagous leaf mining moth (Phyllonorycter blancardella), taking into account the heterogeneous microclimatic conditions provided by its host plant, the domestic apple (Malus domestica), the larval body temperature rather than the ambient air temperature, and a non-linear development rate model. Hourly body temperature dynamics of larvae homogeneously dispersed in tree canopies were simulated from hourly meteorological conditions (medium IPCC climate change scenario) within the canopy of apple trees. To analyse the effect of tree architecture on leaf miner development, both pruned and unpruned trees, and one, two and three scaffold branched trees were used. Body temperature dynamics was used to compute larval development time and mortality following the non-linear developmental model for this insect. The results showed that tree pruning influences significantly larval development time and mortality. Nevertheless, the effects of manipulating tree structure on larval development and survival were relatively weak compared with the impact of chosen climate variations. This survey also showed that the variability in insect development time within a year and insect mortality change markedly with climatic variations, and highlights the importance of using non-linear rate curves and insect body temperatures instead of air temperature in forecasting models of climate-related insect pest outbreaks.