Effect of castor leaf alcohol extract on Diaphania indica
蓖麻叶片粗提物对黄瓜瓜绢螟的作用

Castor plant is increasingly cultivated for use as bio-energy. Castor leaves are also used as bio-pesticides. This study explored the effects of alcohol extracts from castor leaves on Diaphania indica Saunders in cucumber plants. Crude castor leaf extracts were diluted at different degrees to investigate their effects on D. indica feeding on leaves of cucumber plants under greenhouse conditions. 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. indica larvae. The higher the concentrations of the extracts, the less were the consumption and survival rates. When extract was diluted at 200 times, average consumed area of cucumber leaf was 1.89 cm2, which was only 53.7% of the control treatment and 97.7% of treatment with extract diluted at 600 times. At dilution rate of 600 times, survival rate of D. indica larvae was 45.65%, much lower than that of the control (88.89%). Different D. indica larvae instars responded differently to castor leaf extracts. Higher effects were observed at lower larvae ages. When treated with extracts diluted 200 times for 24 h, survival rates of first and fifth instars were 22.22% 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 cucumber leaves treated with crude castor leaf extracts. Under treatment with 200 times dilution of crude castor leaf extracts for 24 h, the first and 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 crude castor leaf extracts were sufficient anti-feedants and poisons to D. indica.