Of all abiotic factors that drive range boundaries, temperature is the best studied because of its pervasive influence on biological processes. For populations at high-latitudes, extreme cold and the populations’ cold-hardiness set the range boundary. Phenotypic plasticity, where a single genotype results in differentiated phenotypes under differential environmental conditions, can assist populations in managing changing temperatures. Local adaptation in phenotypic plasticity, which results in different responses in different populations, can assist with the variability in temperature a species can experience across its range, especially at range boundaries. I used the eastern spruce budworm, Choristoneura fumiferana (Lepidoptera: Tortricidae) as a model system for exploring local adaptation and phenotypic plasticity of insect cold-hardiness. The species is one of the most destructive forest pests in North America, therefore accurately predicting its range and population growth is essential for management. In this thesis, I show that there is no transgenerational plasticity in cold-hardiness. However, I found a fitness cost associated with repeated cold exposures. Additionally, across the species’ range, I found both local adaptation of seasonal cold-hardiness and short-term plasticity of this trait. Therefore, the findings of this thesis provide evidence for including phenotypic plasticity and local adaptation when modelling species distributions under climate change.