To achieve satisfactory management of insect pests of apple and pear, growers must accurately establish the necessity for control actions such as supplementing natural enemy numbers or applying pesticides, and the optimal timing for these actions. Inaccurate determination of these questions can lead to unnecessary or inefficient actions being taken, with undesirable environmental and financial consequences. A project, funded by the British Apple and Pear Research Council, began in 1988 to describe mathematically the population dynamics and phenology of several apple and pear pests. The objective of the research was to develop a suite of simulation models to be used in conjunction with automatic meteorological monitoring equipment to provide a rational basis for decision making in pest management. The models have been thoroughly validated using historical results of pest populations in orchards in south-east England. Output from the models has been satisfactorily accurate, and as a result a delivery system for the models has been developed. This package, named PEST-MAN, has an intuitive style of presentation involving simple pull-down menus, context-sensitive help statements and colour graphics, and allows users to familiarize themselves quickly with the system.