Flavonoids in rice: Ultrasonic extraction and its insecticidal effect on the brown planthopper Nilaparvata lugens Stål

The optimal technological requirements for flavonoids extracting by ultrasonic wave from rice plant (variety ASD7) and the insecticidal effect of the flavonoids on brown planthopper (BPH) were investigated. Four main factors, including ethanol concentration, ratio of liquid to solid, ultrasonic power and extracting time were firstly analyzed by singlefactor analysis, and followed by orthogonal experiments. The condition for extracting flavonoids from rice plant was optimized as following: 70% ethanol, a solid-liquid ratio of 1:25, a power of 250 w, and an extracting time of 50 min. Under these conditions the extraction rates of 5 rice varieties was 0.34% (TN1), 0.38% (Rathu Heenati), 0.36% (ASD7), 0.33% (Mudgo), and 0.28% (Xiushui 11), respectively. The survival rates of BPH fed on artificial diets with different dosages of flavonoids were observed at 24 h and 48 h. When treatment with 0.1 mg/ml extracting flavonoids, the survival rates of BPH were 34.0% (24 h) and 6.0% (48 h), significantly differed from the control (78.0%, 24 h; 32.0%, 48 h). The survival rate of BPH decreased with the increase of the flavonoids concentration, especially, at a concentration of 0.5 mg/ml of extracting flavonoids, no BPH survived for more than 24 h. The results indicated that flavonoids had an insecticidal effect on BPH.