Arthropod Fauna of Conventional and Organic Rice Fields in California

Levels of both pest and nonpest arthropods were compared among four pairs of fields of conventional and organic rice, Oryza sativa L., in California. For seven major pests, there were no significant differences in abundance or in level of damage between conventional and organic treatments. However, in two organic fields, the combination of high infestation level (>5% of rice plants infested) by immature Hydrellia griseola Fallén, an ephydrid leafminer, and low stand densities (<25 plants per 0.09 m2) warranted preventive action to avoid economic loss. Collections revealed a high degree of taxonomic similarity between conventional and organic treatments; species richness did not differ significantly between treatments. However, three predatory taxa—Belostoma flumineum Say, Notonecta spp., and adult Thermonectus basillaris (Harris)—were significantly more abundant in the organic than in the conventional treatment.