Effective decision support tools are required in order to provide agricultural practitioners with advice regarding appropriate and economic pest management strategies. Process-based simulation models could enhance farmer’s abilities to make knowledge-based decisions regarding both the timing and extent to which chemical management is relied upon in an agronomical context. This work describes a new simulation model that quantifies the size and timing of grain aphid populations in response to temperature. The simulation model is comprised of compartmentalised aspects of the aphid’s life cycle, which interact with one another to produce the population dynamics. The model is subjected to an independent evaluation in order to assess its descriptive capacity in comparison with previous simulation models, and is shown to constitute an improved tool to describe the seasonal population dynamics of S. avenae.