Manipulation of Overwintering Habitats for Invertebrate Predators on Farmland.

Abstract

Data are presented from a three-year study on the creation of overwintering habitats in farmland for the arthropod natural enemies of cereal aphids. These new habitats, in the form of grass-sown raised banks, re-created those aspects of existing field boundaries which had previously been shown to favour predator overwintering.
During the first year of establishment, the new habitats provided overwintering refuge sites for many spiders (Araneae), ground beetles (Carabidae) and rove beetles (Staphylinidae), with ground-zone searches producing total densities of these polyphagous predators up to 150 m^-2. In the second and third years, destructive sampling revealed much higher predator numbers, peak densities exceeding 1,500 m^-2 in some grass treatments in the second year. Identification of individual predator species revealed a shift in community structure, with spiders and ground beetles showing successional changes from pioneer to more specialised species as the newly created habitats matured. Beyond this, a range of biotic and abiotic factors were shown to be involved in the processes of successful overwintering and overwintering site selection.Predator sampling studies in the spring showed that the overwintering predator populations in the new habitats could influence subsequent dispersal patterns into the crop, providing an even spread of predators throughout the field early in the season. The results of the study are discussed in the context of the current social and economic climate within European agriculture, and it is suggested that dynamic land management, by enhancing natural pest control, could provide a means of reducing the present-day reliance on chemical pest control measures.