Creation of 'island' habitats in farmland to manipulate populations of beneficial arthropods: predator densities and emigration.
Grass-sown raised earth banks were created as islands in the centres of 2 winter wheat fields in the UK to provide improved overwintering conditions for invertebrate predators. During the 1st year of establishment (1987-88), these areas provided overwintering refuge sites for many species of Araneae, Carabidae and Staphylinidae. Ground-zone searches recorded polyphagous predator densities of up to 150 /m2. During the 2nd year (1988-89), grass establishment increased still further and destructive testing revealed predator numbers exceeding 1500 /m2 in some grass treatments. The overwintering populations affected dispersal patterns of Tachyporus hypnorum and Demetrias atricapillus in the crop. The prospects for the long-term enhancement of predator populations via field scale manipulations of farmland habitats are discussed.