Abstract
Effect of the management of paddy fields on abundance of spiders and their prey insects was investigated in the paddy fields under sustainable cultivation and customary cultivation in Aso area. The densities of spiders and prey were surveyed in the paddy and the levee during 1990-1991 by the sweeping method. Ten to fourteen families of spiders were caught in the study area. Tetragnathid spiders were most abundant, followed by thomisids and clubionids. The spider densities were higher in the sustainable-cultivation field than in the customary-cultivation field. The density and the number of families of spiders were higher on the levee than inside the paddy, suggesting importance of levee as a refuge for spiders. The spider density fluctuated rather synchronously with the densities of planthoppers and leafhoppers. Chironomids were more abundant in the sustainable-cultivation fields and may maintain high spider density in these fields when the hopper density was low. These results suggest that constant prey supply and reduced weeding on the levee serve to increase the spider density.
