As with all post mortems the aim is to work out what happened and why. By understanding this we will be better able to address the issue of how much of Australia's cotton will be affected by this pest and what is the level of the threat. A good starting point is the basic set of requirements for a silverleaf whitefly outbreak and here we need to consider the &quote;outbreak pyramid&quote; (Fig. I, modified after Peter Ellsworth, University of Arizona, Maricopa). The two most critical factors are climate and cropping systems, without both of these an outbreak is unlikely.