THE EFFECTS ON BENEFICIAL ARTHROPODS OF THE EXCLUSION OF HERBICIDES FROM CEREAL CROP EDGES

(1) The arthropod faunas of herbicide-treated and untreated headland plots of a spring wheat crop were compared in a replicated within-field experiment in Hampshire, England. (2) Unsprayed headland plots had more weed species, higher weed densities, greater weed biomass and a higher percentage weed cover. (3) Unsprayed headland plots supported significantly higher densities of non-target arthropods, especially the non-pest species which are important in the diet of insect-eating gamebird chicks. These plots also contained higher densities of predatory arthropod groups, especially the polyphagous species and their alternative prey. (4) Within plywood enclosures placed in treated and untreated headland plots, no significant between-treatment differences were found in the total pitfall trap catch of the two most numerous carabid beetle species, Pterostichus melanarius (Illiger) and Agonum dorsale (Pontoppidan). However, a significantly greater proportion of female A. dorsale were caught in the enclosures in treated plots than in untreated plots. (5) Dissection revealed that significantly more gut sections of gravid and non-gravid female and male P. melanarius and gravid female and male A. dorsale from untreated plots contained solid arthropod food remains. Both carabids had also taken significantly more meals and preyed upon a wider variety of arthropod food in untreated plots. As a consequence fewer cereal aphids were consumed by beetles in unsprayed plots. (6) Higher numbers of eggs per female were found for both species of carabid beetle collected from untreated plots. (7) The consequences of the changes in the pesticide use on the edges of cereal fields to pest-predator relationships are discussed.