Indirect effects of nutrients in organic and conventional paddy field soils on the rice grasshopper, Oxya japonica (Orthoptera: Acrididae), mediated by rice plant nutrients

Abstract

Current agricultural technology depends on synthetic fertilizers and enhances the growth of herbivorous insect populations. Some organic farming uses bio-based nutrients instead and is considered the most promising way to mitigate the negative effects of conventional farming. The rice grasshopper Oxya japonica (Thunberg) (Orthoptera: Acrididae) is the most abundant herbivore in both conventional and organic fields in northern Japan. This study investigated the effects of soil nutrients associated with conventional versus organic farming on rice plant quality,and the growth and performance of O. japonica in paddy fields at Sakata, Yamagata Prefecture. A laboratory experiment was also conducted to understand the effects, as mediated by host plant quality, of organic and conventional soil nutrients on the growth and feeding (as measured by the leaf area consumed) of O. japonica. Nymphs of O. japonica that fed on nitrogen-rich, carbon-poor plants cultivated in conventional soil grew and developed faster than those feeding on organic plants. The rice plants in conventional fields had greater biomasses, suggesting that they were more likely to tolerate grasshopper damage. These results support the importance of soil nutrient management as a factor that influences plant–herbivore interactions.