The reasons for assessing crop losses due to pests of cereals are reviewed; for making decisions in pest management based on costs and benefits, for allocating resources on the most important pests, and as a guide to how yield is lost. Crop yield is seen as a balanced system, with inputs and output. The methods of quantifying pest attack, measuring losses and the difficulties met are discussed: the interaction of losses, interplot interference, mixed crops, loss distribution and crop compensation. Surveys of loss are described, with examples.
