IMPLEMENTING THE SYSTEMS-APPROACH IN PEST-MANAGEMENT

Three broad phases may be distinguished in the application of the systems approach to pest management. Prior to about 1970, much emphasis was placed on the development of concepts and modeling techniques; in the 1970s and early 1980s, a series of pest simulation models for kev pests was developed,- and, in the late 1980s, some crop and socio-economic factors were incorporated to develop decision-aids for farmers and extensionists. Significant advances have been made in methodology at three levels-Level 1 on pest constraint characterization and pest management domain definition, Level 2 on quantitative and qualitative descriptions of the pest-crop-ecosystem interfaces, and Level 3 on the development of specific tools for applying systems techniques in pest management. The three levels are interlinked, as shown in several crop-pest ecosystems such as potato pests in the Mid-Western USA, groundnut diseases in West Africa, and rice pests in Tropical Asia. Analysis of pest profiles over time, resulting in the characterization of relationships among components of a system and improved system definition, has resulted in more focussed analysis of sub-systems. Pest simulation models commonly simulate the dynamics of single diseases or insects as they are affected by the host and physical environment. Pest or pest-crop models find little application for pest management unless they are used within the context of the socio-economic-factors influencing the considered system and are adapted to the application domain. This has been accomplished in several ways. Simplified pest models or simplified decision rules from crop-pest models with economic values assigned to their outputs have been used for managing several pathosystems. Predictive models have been used to define zones of equivalent pest risk to guide extrapolation of pest management technology, from key sites to a broader area, and to deploy host plant resistance. For agricultural development and, more specifically, for an accelerated adoption of the systems approach in pest management, a toolkit may have to be developed to reduce the lag time between generation of global principles and development of site-specific management tactics and strategies.