Abstract:Bradysia odoriphaga Yang et Zhang larvae were fed with leek, garlic, onion and scallion, respectively. The susceptibilities of the fourth instar larvae to garlic oil, sophocarpidine and phoxim were studied using dipping method. Effects of dichlorvos and garlic oil on the activities of acetylcholinesterase (AChE) and some main metabolizing enzymes in the larva were also studied by biochemical analysis method. The LC50 values of garlic oil to the larvae fed with leek, garlic, onion and scallion were 825.14 mg/L,1 202.2 mg/L,1 274.3 mg/L and 1 412.4 mg/L, respectively, and those of phoxim were 0.5437 mg/L,1.1921 mg/L,1.7713 mg/L and 1.9224 mg/L. Significant differences of the LC50 values were observed between the larvae fed with garlic and onion and fed with leek. Compared with the activity of acetylcholinesterase (AChE) of the larva fed with leek, the activities of AChE of the larva fed with garlic and onion were depressed, but that of carboxyleterase was obviously increased, and that of glutathione-S-transferase was relatively increased. The induction or the restraint of the acetylcholinesterase and other related metabolizing enzymes by the thioether compounds in the host plants might be the main reason to cause the differences in the pesticide susceptibility of the larvae.