Rising fossil fuel prices, energy security and adherence to existing European Union (EU) climate/energy policies means that Ireland must look towards alternative energy sources to meet future demand. Woody biomass in the form of short rotation coppice willow (SRCW) is considered a viable option. SRCW is vulnerable to damage by a range of diseases and pests however. The blue (Phratora vulgatissima) and brown (Galerucella lineola) willow beetles (Coleoptera: Chrysomelidae) are identified economically as two of the most damaging insect pests of SRCW in Ireland. Policies which mandate levels of renewable energy use, to mitigate future climate change, fail to consider adaptation in the energy sector under increased levels of pestilence due to projected changes in the climate system. The effects of abiotic and biotic factors, mainly temperature and photoperiod, but also host plant, on beetle development were investigated. Constant temperature experiments showed that development time for all assessed life-cycle stages decreased as temperature increased. P. vulgatissima oviposition period and total fecundity were influenced by temperature also. Development was not found to vary considerably when P. vulgatissima larvae were reared on different host plant varieties (Tora, Resolution, Tordis and Inger) across a similar range of constant temperatures. A critical daylength (CDL) for P. vulgatissima facultative reproduction was calculated. The relationship between temperature and P. vulgatissima and G. lineola life-cycle stage development was represented by applying criteria satisfying non-linear deterministic and stochastic functions to development rates and development time distributions respectively. A combined phenology/voltinism model was constructed incorporating a Salix. viminalis degree-day budburst model, the temperature-dependent development rate and temperature-independent time distribution functions, and information regarding the reproductive diapause inducing CDL. Using observed temperature and statistically downscaled climate scenarios derived from different global climate models (GCMs) forced with different emission scenarios, model results suggested important spatio-temporal changes in the life cycle and voltinism of P. vulgatissima, including two annual generations for 5% and 50% beetle emergence proportions (E.P) at all observed locations nationally by the 2050s and three annual generations for 5% E.P for a percentage of years at certain inland and south-westerly observed locations by the 2080s. The findings from this research may have implications for regional SRCW production, integrated pest and crop management and climate and energy policy in the future.