3. Reductions of natural enemies around means that natural enemies of pests more must come to the crop from increasingly small and more distant non-crop reservoirs, entering crops too late or in too little numbers to prevent pest outbreaks
4. Intensification results in a reduction of intervals between plantings of the same crop, or overlap of crops, which provides a continuous resource to pests.
5. The search for better cultivars and accelerated movement of plant material around the world and with it the movement of pests. Plant breeders, commercial importers, distributors of food aid and general commerce inadvertently introduce pest species. 6. Virtual reliance on chemicals leading to an increase in pest problems particularly for insects