The crop field is in dynamic interaction with its abiotic and biotic environment and not an island onto itself. Pests (e.g. aphids), natural enemies (e.g. ladybeetles, carabid beetles and parasitoids), pollinators (e.g. wild and managed honeybees), spores of pathogenic micro-organisms (e.g. spores of Phytophthora infestans), and weed seeds (e.g. Cirsium arvense) travel in the wider landscape, often by aerial dispersal, but in the case of some insects, also by walking.