The repellent activities of plant ethanolic extracts and their derived compounds against three species of rice planthoppers and their potential side-effects on the main predator, Cyrtorhinus lividipennis

The brown planthopper ( Nilaparvata lugens , BPH), white-backed planthopper ( Sogatella furcifera , WBPH) and small brown planthopper ( Laodelphax striatellus , SBPH) are three serious pests in the rice cultivation of Asia. Using plant extracts or their derived compounds to control rice planthoppers could be sustainable, as they are reliable sources of bio-pesticide. In this study, we evaluated the repellency of eighteen plant ethanolic extracts and their derived compounds against these planthoppers. Our results indicated that ethanolic extracts from Litsea cubeba , Zanthoxylum bungeanum , Piper nigrum , Curcuma longa , and Cinnamomum camphora possessed repellency effects on female adults and nymphs of BPH. The petroleum ether fractions of L. cubeba , Z. bungeanum , and C. longa ethanolic extracts, the ethyl acetate fractions of P. nigrum ethanolic extracts were analyzed with GC–MS. Based on earlier reports and our GC–MS analysis, nine compounds derived from the above ethanolic extracts were selected to screen their repellency to BPH in H-tube olfactometer. Two effective compounds, 1-(2-hydroxy-4, 6-dimethoxyphenyl)-ethanone (xanthoxyline) and caryophyllene oxide, were chosen to investigate their repellency on three species of rice planthoppers. The two compounds showed significant repellency to BPH, WBPH and SBPH under laboratory and greenhouse conditions at 10–1000 ppm. Field experiments showed that the releasers which contained 1000 ppm xanthoxyline or caryophyllene oxide suppressed the planthoppers population significantly. Additionally, xanthoxyline and caryophyllene oxide showed no adverse effect on the predator, Cyrtorhinus lividipennis , in the laboratory and field conditions. These results may contribute to the IPM program for the development of green planthoppers repellents applied in the rice field.