Spatial Scales in Ecological Pest Management (EPM): Importance of Regional Crop Rotations

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Abstract
The importance of spatial scales and landscape heterogeneity to insect populations is widely accepted in ecology and conservation biology. What are the applications to crop protection? Theoretically, insect pest species with certain characteristic metapopulation dynamics may effectively be managed by crop rotation, by applying the same tools as used in conservation. This strategy may in many cases necessitate regionally planned rotations that exceed single farm boundaries. The basic idea of pest management by regional crop rotation is presented, the theoretical background outlined and agroecological prerequisites discussed. Spatiotemporal patterns of both pest occurence and the host crop field allocation in the landscape are important. For example, the required degree of isolation between host crop patches cannot be achieved with regionally covering major crops, e.g. cereals. The dispersal ability of the pest determines the overall spatial scale at which the rotation is practised. Recruitment from wild hosts must not be excessive. These aspects are illustrated with example species, the cabbage root fly, Delia radicum, a possible target for regional management, and the rape pollen beetle, Meligethes aeneus, an unlikely target. Regional rotation and biological control are not conflicting strategies, as the crop-pest systems most promising for regional management are the least promising for biological control.