Variation in the Distribution of Carabid Beetles in Cereal Field Headlands.
In the Breckland Environmentally Sensitive Area scheme, farmers are encouraged to establish either an 'Uncropped Wildlife Strip' (no crop sown and restricted application of pesticides) or a 'Conservation Headland' (crop sown and restricted use of pesticides) in the outer 6 to 12 m of cereal fields. These were compared with headlands which received a full complement of agricultural applications.
In early Spring the uncropped wildlife strips consisted of predominantly bare ground. By July they became the most complex habitat with the most dense vegetation cover, particularly of dicotyledonous species. They also had greater foliage height diversity and more soil-surface active invertebrates than either the conservation or sprayed headlands.
Carabid abundance and species richness were positively correlated with vegetation cover, in particular by dicotyledonous plants. Consequently there were more individuals of more species of carabid in the uncropped wildlife strips than in the other headland treatments. Individual species varied in their response to ground cover. Bembidion lampros preferred bare ground and was most abundant in the uncropped wildlife strips early in the season. Pterostichus melanarius, Agonum dorsale and Trechus quadristriatus avoided the bare ground in the uncropped wildlife strips in Spring. Harpalus affinis, Harpalus rufipes and Amara aenea preferred dicotyledonous vegetation and were most abundant in the uncropped wildlife strips early in Summer.
The presence of the uncropped wildlife strips delayed the dispersal of A. dorsale into the field from an adjacent field boundary, but not significantly so and, although attracting high densities of many species, they did not affect their activity in the adjacent crop.
In conclusion the uncropped wildlife strip had the greatest value for the conservation of carabids and other wildlife including natural enemies of cereal aphids. This was reflected in significantly lower densities of cereal aphids in the crop adjacent to this headland treatment.