The Impact of Field Boundary Habitats on the Diversity and Abundance of Natural Enemies in Cereals

Abstract

Semi-natural biotopes of agricultural landscapes take the form of linear and insular structures which remain in predominantly cultivated areas (Lubbe, 1988). The linear structures are typically grass boundaries or hedges between fields, along farm tracks, roadsides, drainage ditches, water courses and forest edges (Greaves and Marshall, 1987). These semi-natural, remnant biotopes have been included in recent ecological studies of agricultural ecosystems because they provide habitat for farmland gamebird species (Potts, 1980; Sotherton, 1991), wildlife, in particular, song birds (Parish et al., 1994) and butterflies (Dover, 1991). They were also considered to influence the species composition and population size of natural enemies in arable fields which were either the stenophagous predators or parasitoids of crop pests (van Emden, 1965) or polyphagous, generalist predators, which predate on crop pests only as part of a general diet which is typically composed of arthropods, mycoflora and herbage (Sotherton, 1985; Coombes and Sotherton, 1986). It was suggested that the densities of these predators of insect pests in crop fields may be increased by these adjacent habitats because they could provide shelter, breeding sites and sources of alternative food (Hagen et al., 1976).