Determination of the Susceptibility to Three Insecticides and the Activities of Three Enzymes of Diaphania indica

A study was carried out on the susceptibility to cyhalothain, phoxim and abamectin and the activities of AchE, carboxylesterase and MFO of three field strains of Diaphania indica which were collected from Danzhou city, Ledorig and Chengmai counties/cities respectively. The results of the mensuration showed that the susceptibility to cyhalothain, phoxim and abamectin and the activities of AchE, carboxylesterase and MFO of Diaphania indica varied with strains. Chengmai strain had the least susceptibility to cyhalothain and phoxim compared to Danzhou and Ledong strains, and the strain of Ledong demonstrated the least susceptibility to abamectin compared to Chengmai and Danzhou strains. The LD50 values of cyhalothain and phoxim for Chengmai strain were 5.088 4 mg/g and 12.543 7 mg/g, whereas for Danzhou strain 3.045 4 mg/g and 7.598 6 mg/g and for Ledong strain 3.382 9 mg/g and 3.811 2 mg/g. The LDx values of abamectin for Danzhou, Ledong and Chengmai strains were 0.022 8 mg/g, 0.041 6 mg/g and 0.012 4 mg/g. The activities of AchE, carboxylesterase and MFO were the highest in Chengmai strain, which were 14.660 5 mmoL/(mg·min), 22.329 9 mmoL/(mg.min) and 8.827 4 mmoL/(mg·min) respectively. The activities of AchE and MFO of the Ledong strain and carboxylesterase of the Danzhou strain were the lowest, which were 5.380 4 mmoL/(mg·min), 3.362 5 mmoL/(mg·min) and 8.085 6 mmoL/(mg·min). Based on the test results, it could be inferred that the higher activity of carboxylesterase is one of the major factors that enhance the resistance of Indian cabbage moth to cyhalothain, and the increased activities of AchE and MFO act as the important factors that decrease the susceptibilities of Indian cabbage moth to phoxim. It seemed that AchE, carboxylesterase and MFO did not exert dominant influences on the susceptibilities of Indian cabbage moth to abamectin.