The Effect of Drosophila release on the Spider Popuration in a Paddy Field

Abstract

Drosophila flies were released into dikes surrounding a paddy field during the period from late April to mid-July as an alternative prey of spiders. Flies were found to be devoured frequently by spiders and constituted 39% of the spider diet. The population density of spiders in the dikes increased soon after release and was followed by an increase in paddy fields situated adjacent to the dikes. The population density of leaf- and planthoppers inhabiting these plots was suppressed during late July in the dikes and during early September in the paddy fields, but the suppression was not evident thereafter. These results suggest that the abundance of spiders in any given paddy field depends upon the extent of food availability prior to migration from dikes, and that their predatory pressure upon hoppers is not significant.