Numerous studies have shown the impacts of climate change on species distributions and extinctions, but the mechanisms through which climate variations influence individuals and populations remain poorly understood. This lack of knowledge severely hampers our ability to forecast and anticipate the effects of climate change on multitrophic relationships. The key to forecasting the effect of climate change is an understanding of the microclimate that organisms actually experience and how microclimate will be altered by global change. The project aims at determining both direction and amplitude of the climate change impacts on the population dynamics of a phytophagous spider mite feeding on apple leaves. The project will reveal the mechanisms through which climate change affects individuals and populations directly and also indirectly by altering the biotic interactions within the spider mite microclimate. The project will explore whether organisms such as insects or arachnids have the possibility to move over short distances within the local spatial scales (leaf surface, tree canopy) to buffer against extreme climatic events such as heat waves that happen at a global scale. A biophysical modelling approach will be developed as it allows to identify the precise mechanisms involved by integrating the heat budgets of the organisms. A biophysical modelling cascade will be established in order to predict the body temperature of a spider mite at a given position on a leaf surface, within the tree canopy architecture, and under a specified regional climate. This integrative approach will allow us to map favourable and risky microclimates for spider mite survival. Then, the biophysical modelling cascade will be connected to a population dynamics model to assess the consequences of spatial thermal heterogeneity in microclimates at the population scale. This framework will be used to quantify the amplitude of the micro-climatic change, and its effects on spider mite population dynamics, driven by the climate change scenarios elaborated by the IPCC. Finally, the project will lead to comprehensive predictions on the response of spider mite populations to climate change (outbreaks, local extinctions). This project is therefore at the interface between fundamental research on thermal ecology, population dynamics and applied ecology that provides policy makers and conservation biologists with tools to anticipate the negative impacts of climate change on agricultural systems.