The Lethal Mechanism of Trap Plant Vetiveria zizanioides Against the Larvae of Chilo suppressalis

【Objective】 Vetiver grass (Vetiveria zizanioides) can effectively attract female adults of Chilo suppressalis to lay 3 期 鲁艳辉等:诱集植物香根草对二化螟幼虫致死的作用机制 487 eggs, while the larvae can not complete their life cycles by feeding on vetiver. The objective of this study is to illuminate the lethal mechanism of trap plant-vetiver against the larvae of C. suppressalis and provide a theoretical basis for the development of sustainable control technology for C. suppressalis based on the application of trap plant vetiver in rice based ecosystem. 【Method】 The toxic substances were extracted from vetiver by the methods of extraction and silica gel column chromatography, and the biological activities of these extracts against 3rd instar larvae of C. suppressalis were determined by mixing them in the artificial diet. The nutrient contents of rice and vetiver, and the detoxifying and digestive enzymes activities of C. suppressalis larvae fed on rice and vetiver were analyzed using biochemical methods. 【Result】 The mortalities of the C. suppressalis 3rd instar larvae after 9, 12, 15 days treated by sherwood oil extract of vetiver were 38.89%, 57.41%, and 85.19%, respectively, which were significantly higher than the mortalities of larvae treated by ethyl acetate extract, n-butyl alcohol extract and other fractions. The fraction 1 (Fr1) and fraction 5 (Fr5) were isolated and obtained from sherwood oil extract of vetiver, and the mortalities of C. suppressalis the 3rd instar larvae to Fr1 and Fr5 (0.05 g·mL) were 85.00% and 67.67% after 3 days treatment, respectively. These results indicated that vetiver contains toxic substances, which have lethal effect on C. suppressalis larvae. Results of nutrient contents determination showed that the contents of total protein, cellulose, total sugar and amino acids in vetiver were 9.45 μg, 1.61%, 1.45%, 4.00%, respectively, significantly lower than those in rice, and the methionine (MET) content in rice was 7-fold higher than that in the vetiver. However, the content of tannin was 1.31-fold higher than that in rice. In addition, the protease, amylase, trehalase and sucrase enzyme activities of C. suppressalis larvae on 3rd day after fed (DAF) on vetiver were significantly lower than those in the larvae fed on rice; and on the 6th DAF, the activity of P450 enzyme in the larvae fed on vetiver was significantly lower than that in the larvae fed on rice; and the esterase activity of C. suppressalis larvae on the 9th DAF on vetiver was significantly lower than that in the larvae fed on rice. Compared to glutathione S-transferase (GSTs) activity of the 3rd instar larvae feeding on rice, the enzyme activity of the larvae feeding on vetiver was also decreased, however, there was no significant difference by statistical analysis. 【Conclusion】 Vetiver as a dead-end trap plant of C. suppressalis, there were probably two lethal mechanisms of vetiver against C. suppressalis. Firstly, vetiver contains toxic substances, which have lethal effect on C. suppressalis and these substances inhibited the esterase and cytochrome P450 enzyme activities, leading to the function loss of larvae in detoxification and metabolism. Secondly, compared to rice, lack of nutrients in vetiver can not meet the demand of the larvae, and led to digestive function and physiological activity disorder and ultimately death.