Abstract:

In order to investigate the mechanism of acaricidal activity of Mentha piperita extracts against Tetranychus cinnabarinus, adult spider mites were treated with 2 mg ·mL^-1 eluted fraction V of M. piperita extracts in vitro, and the resulting acaricidal symptom and ultrastructure were observed. Furthermore, the enzyme activity of monoamine oxidase (MAO), glutathione-S-transferase (GSTs), acetylcholine esterase (AchE) and proteinase in the treated mites was examined. The results illustrated that the toxic symptom of the treated mites experienced four different phases, namely quiescence, activity, convulsion and death. The ultrastructural observation by the electronic microscope indicated that the control had an intact subcellular structure, while the treated mites were severely damaged and their subcellular structure was hardly identified. The enzyme activities of spider mites varied after being treated with M. piperita extracts. MAO activity was boosted up, especially at the 12^th and 24^th h after treatment (P<0.05). The GSTs activity was intrigued after treatment and exhibited an increasing trend during 4-24 h,suggesting that the poisonous component accumulated in T. cinnabarinus and mobilized GSTs for the detoxification. Meantime, the AchE and proteinase activity were inhibited by M. piperita extracts. It suggested that the transfer of nerve impulse was possibly interdicted and the digestive system was maladjustedd.

Key words: Mentha piperita, Tetranychus cinnabarinus, activity of enzyme, ultrastructure