Community Structure and Regulatory Mechanism of Pest Populations in Rice Paddies Cultivated Under Intensive, Traditionally Organic and Lower Input Organic Farming in Japan

Abstract

ABSTRACT Three different rice production systems in the Chugoku district of southwestern Japan were compared to characterize differences in the arthropod community structures and insect pest regulatory mechanisms. In older traditionally organic rice paddy fields, Nilaparvata lugens was uncommon and was controlled by the sedentary nematode parasite, Agamermis unka. In contrast, in intensively farmed rice paddies, N. lugens was very abundant and A. unka was absent. There were no differences between the intensive paddies and younger traditional paddies. In addition, differences of abundance in spider and collembola populations were not clear in these paddies. In lower-input organic farming systems with no-tillage and winter legume mulch, Sogatella furcifera was much less abundant, and the most important predators, sedentary lycosids, were much more abundant than in the traditionally managed paddy. Densities of N. lugens were similar, but A. unka was not present in the lower-input organic systems. These sedentary natural enemies were more abundant in paddy fields farmed with less soil surface disturbance.