Abstract: 【Aim】The purpose of this study is to explore the physiological and biochemical responses in rice plants to the stress imposed by different densities of the adult brown planthopper (BPH), Nilaparvata lugens for different time.【Methods】The contents of chlorophyll (Chl) and total protein (TP), and the activities of lipoxygenase (LOX), total superoxide dismutase (T-SOD), peroxidase (POD) and polyphenol oxidase (PPO) in rice plants fed by N. lugens adults at the densities of 2, 4 and 8 individuals/plant for 6, 24, 48 and 96 h were tested by biochemical methods.【Results】At 6 h after being fed by N. lugens adults at the low density (2 individuals/plant), the Chl content in rice plants decreased significantly and the TP content and PPO activity in rice plants increased significantly, while the Chlb and total Chl contents, TP content and activities of LOX and POD in rice plants at 6 h after being fed by N.lugens adults at the high density (8 individuals/plant) increased significantly as compared to those in the control group non-inoculated with N. lugens adults. Compared to the control group, the stress imposed by low density of N. lugens adults resulted in significantly reduced Chl content and PPO activity, and significantly enhanced activities of LOX, T-SOD and POD in rice plants, and that imposed by high density of N. lugens adults caused significantly increased Chl content and PPO activity, and significantly decreased activities of T-SOD and POD in rice plants at 24 h. In rice plants fed by N. lugens adults at the low density and medium density (4 individuals/plant), the Chl content and activities of T-SOD and POD decreased significantly, and the TP content significantly enhanced at 48 h, while in rice plants fed by N. lugens adults at the high density, the Chl content and T-SOD activity significantly reduced and the TP content and POD activity increased significantly at 96 h, as compared to those in the control group. 【Conclusion】The stress imposed by different densities of N. lugens adults for different time induces changes in the contents of Chl and TP, and activities of LOX, PPO, T-SOD and POD. The change intensity and response time are obviously different due to the feeding density of N. lugens adults.

Key words: Nilaparvata lugens, feeding stress; Oryza sativa, induced reaction, enzyme activity