CREATION OF ISLAND HABITATS IN FARMLAND TO MANIPULATE POPULATIONS OF BENEFICIAL ARTHROPODS - PREDATOR DENSITIES AND EMIGRATION

(1) Grass-sown raised earth banks were created as 'islands' in the centres of two cereal fields to provide improved overwintering conditions for invertebrate predators. They recreated those aspects of existing field boundaries which had previously been shown to favour predator overwintering. (2) During the first year of establishment, the new habitats provided overwintering refuge sites for many species of Araneae. Carabidae and Staphylinidae. Ground-zone searches produced total polyphagous predator densities of up to 150 m-2. (3) During the second year, grass establishment increased still further and destructive sampling revealed predator numbers exceeding 1500 m-2 in some grass treatments. (4) Vacuum-net samples taken during the second spring after establishment, showed that the overwintering populations of two predator species in the new habitats influenced dispersal patterns into the crop. (5) Prospects for the long-term enhancement of predator populations via field scale manipulations of farmland habitats are discussed.