Abstract
Cereal aphid studies form the backbone of this chapter and will be discussed at length, but shall also occasionally discuss the dynamics of aphids that use other annual crops and trees as their host. The overall purpose is to outline the components of an aphid population that determine its dynamics, then discuss how to frame a process-based model and review some of the important issues and decisions that arise as a result. The chapter introduces first the main characteristics of aphid populations and then move on to the concept of forcing (driving) variables, processes and their functions that will be of general applicability to all crop aphids, but often referring to the model species, Sitobion avenae. In this chapter, a process-based model is defined to be a mechanistic model that incorporates processes using difference, differential or rule-based equations. It is hoped that this chapter will reach a broad audience that may not otherwise have the mathematical skills required to read many of the citations used. The chapter concludes with an overview of the challenges that face modellers in their quest to predict aphid population dynamics.