Annual cropping systems consist of a shifting mosaic of habitats that vary through time in their availability and suitability to insect pests. Agroecosystem instability results from changes that occur within a season with crop planting, development, and harvest. Further instability results from continuous alterations in biotic and abiotic insect life system components and from agricultural inputs. Changes to agroecosystems occur across seasons with changing agricultural practices, changing cropping patterns, and technological innovations. Much of this instability is a result of events unconnected with pest management. The abilities of polyphagous pest species to move among and utilize different habitat patches in response to changes in suitability enable the pests to exploit unstable cropping systems. These pest characteristics determine the location and timing of damaging populations. Habitat suitability is influenced by plant species and cultivar, crop phenology, and agricultural inputs. Pest movement is affected by a suite of intrinsic factors, such as population age structure and mobility, and extrinsic factors, including weather systems and habitat distribution. The life systems of three selected polyphagous pests are presented to demonstrate how an understanding of such systems in agricultural ecosystems improves our ability to predict and hence manage these populations.