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 fie lds were paired with adjoining conventional ones and their invertebrat e fauna compared with a D-vac vacuum suction sampler. Weed counts show ed greater percentage cover of broad-leaved weeds in organic fields th an in conventional ones, with three times as many species present wher e herbicides were not used. Significantly higher densities of nematoce ran and acalypteran Diptera, Hemiptera (especially aphids), aphid-spec ific predators, parasitic Hymenoptera and cryptophagid and cantharid C oleoptera were found in conventionally grown fields. Significantly hig her densities of weevils, spiders, springtails, plant hoppers and sawf ly larvae were found in organic fields. Reasons for these differences or the lack of them are discussed.