Abstract: The predatory capacities and functional responses of the mirid bug, Cyrtorhinus lividipennis Reuter, on the brown planthopper (BPH), Nilaparvata lugens Stal, on rice plants with different nitrogen contents and the effects of the rice sap and BPH honeydew on its predatory function were determined in the laboratory at International Rice Research Institute (IRRI), Philippines. The results showed that the predatory capacities of C. lividipennis on BPH eggs and young nymphs were negatively related to the nitrogen content of host plants, while no significant difference in predatory capacities was recorded betweenC. lividipennispopulations successively fed on host plants applied with 0 kg N/ha and 200 kg N/ha nitrogen fertilizer for 2 generations. The functional responses of C. Lividipennis populations on BPH eggs belonged to typical Holling II, and theinstantaneous rate of discovery (a) and handling times (T_h) were strongly affected by nitrogen contents in host plants. The instantaneous rate of discovery reduced obviously resulted in the lower functional responses on the host plants applied with high nitrogen rate; however, the similar response shapes of different populations were found on the plants with the same nitrogen regime. Furthermore, the influences of rice sap from the plants and honeydew of the BPH females fed on the plants with high nitrogen regime on the extension of longevities of the adults of C. lividipennis were higher than those on the plants with low nitrogen regime. However, the honeydew of BPH on the plants with high nitrogen regime significantly decreased the predatory capacity of C. lividipennis on BPH eggs. These results implied that the reduction of C. lividipennis natural control function should be one of the crucial factors to induce the outbreak of BPH population in rice fields applied with excessive nitrogenous fertilizer.

Key words: Cyrtorhinus lividipennis, Nilaparvata lugens, rice, nitrogenous fertilization, predatory function