Abstract: Castor plant is increasingly cultivated for use as bio-energy. Castor leaves are also used as bio-pesticides. This studyexplored the effects of alcohol extracts from castor leaves on Diaphania indica Saunders in cucumber plants. Crude castor leaf extractswere diluted at different degrees to investigate their effects on D. indica feeding on leaves of cucumber plants under greenhouseconditions. The changes in feeding amounts, survival rates and detoxification enzyme activities of D. indica were measured.The results showed that crude castor leaf extracts significantly inhibited the food consumption and the survival rates of D. indicalarvae. The higher the concentrations of the extracts, the less were the consumption and survival rates. When extract was diluted at200 times, average consumed area of cucumber leaf was 1.89 cm², which was only 53.7% of the control treatment and 97.7% oftreatment with extract diluted at 600 times. At dilution rate of 600 times, survival rate of D. indica larvae was 45.65%, much lowerthan that of the control (88.89%). Different D. indica larvae instars responded differently to castor leaf extracts. Higher effects wereobserved at lower larvae ages. When treated with extracts diluted 200 times for 24 h, survival rates of first and fifth instars were22.22% and 66.67%, respectively. Compared with the fifth instar, survival rate of the first instar was only one-third. Gluthione transferase,carboxylesterase and functional oxidase activities in D. indica larvae increased rapidly after D. indica larvae fed on cucumberleaves treated with crude castor leaf extracts. Under treatment with 200 times dilution of crude castor leaf extracts for 24 h, the firstand fifth instars of D. indica larvae were 23.79% and 78.02% higher in gluthione transferase activity, 72.42% and 23.84% higher incarboxylesterase activity and 100.58% and 122.39% higher in functional oxidase activity, over those under the control. With increased dose of crude extracts, an obvious increase in detoxification enzyme activity was noted. The results indicated that crudecastor leaf extracts were sufficient anti-feedants and poisons to D. indica.