Three species of planthopper,Nilaparvata lugens,Sogatella furcifera, andLaodelphax striatellus, showed characteristic behavior of stylet probing in parenchymal tissues of plants. Feeding experiments of planthoppers on aqueous sucrose solution containing the extract of rice plants or barnyard grass revealed the presence of the stimulant for the probing behavior in the plant tissues. EightC-glycosylflavones which stimulated stylet probing were isolated from rice plants. Four of them were identified to be schaftoside, neoschaftoside, carlinoside, and neocarlinoside, the last one being a new compound isolated from the plant. The isolatedC-glycosylflavones showed the same level of the activity for the probing ofN. lugens as the rice plant extract only when all of them were combined.