A COMPARISON OF THE FLORA AND ARTHROPOD FAUNA OF ORGANICALLY AND CONVENTIONALLY GROWN WINTER-WHEAT IN SOUTHERN ENGLAND

Fields of winter wheat on organic and conventional farms were sampled for weeds and invertebrates in June/July in 1990 and 1991. Organic fields were paired with adjoining conventional ones and their invertebrate fauna compared with a D-vac vacuum suction sampler. Weed counts showed greater percentage cover of broad-leaved weeds in organic fields than in conventional ones, with three times as many species present where herbicides were not used. Significantly higher densities of nematoceran and acalypteran Diptera, Hemiptera (especially aphids), aphid-specific predators, parasitic Hymenoptera and cryptophagid and cantharid Coleoptera were found in conventionally grown fields. Significantly higher densities of weevils, spiders, springtails, plant hoppers and sawfly larvae were found in organic fields. Reasons for these differences or the lack of them are discussed.