| l.contact toxicity of crude extracts from thirty-one acaricidal plants in northeastern China against Tetranychus cinnabarinus The acaricidal activities of petroleum either, chloroform and methanol crude extracts from thirty-one plant species were evaluated against Tetranychus cinnabarinus, a phytophagous spider mite. when concentration was lmg/mL, the crude extracts were tested and the mites' mortalities were observed. The results showed that the mortality rate of seven plant species dissolved by petroleum either, four species by chloroform, and one species by methanol are more than eighty percent. The most effective crude extract is Xiangru (Elsholtzia stauntoni) dissolved by petroleum either, with the mortality rate of 100%. Duncan's test showed that the contact toxicity of some species from Northeastern China are different from each other significantly at P<0.05. Three plant species in the family of Labiatae showed a positive effect against T. cinnabarinus, and LC50 of three different peppermints in this family against the immature T. cinnabarinus are 0.4294mg/mL,0.5061 mg/mL and 0.5917 mg/mL respectively.2.Isolation and identification of the acaricidal substance extracted from Mentha piperita The objective of this study was to measure the toxicity of acaricidal active substance of Mentha piperita extracts, to isolate and to identify the chemical compounds of the extracts. Leaves of Mentha piperita were extracted using petroleum ether, chloroform and methanol respectively as solvents. Liquid-liquid partition technique was used to separate the chemical compounds. The acaricidal active substance was obtained by silica gel column chromatography and thin layer chromatography(TLC). The bioactivity was traced by killing Tetranychus cinnabarinus adults and eggs in vitro. Finally, the components of acaricidal active substance was identified by using UV photospectrum, HPLC, IR and MS methods. The effect of acaricidal active substance extracted from Mentha piperita against the adults of Tetranychus cinnabarinus was examined. Compared with those crude extracts from chloroform and methanol, the acaricidal active substance extracted using petroleum ether was more effective, with mortality rate of 87.05% against adult mites and 93.16% against the eggs. The Duncan's test showed that the contact toxicity of the crude extracts from different solvents was significantly different from each other (P<0.05). The crude extracts from petroleum either was separated by liquid-liquid partition techniques. It indicated that the acaricidal active substance existed in the petroleum ether fraction. The concentrated extracts of petroleum ether was separated into eight fractions, among which the fraction V produced significantly stronger acaricidal activity than other fractions. The mean lethal concentration (LC50) was 0.5464mg/mL and 95% confidence limit was 0.3268～0.9134 mg/mL. The purity of the purified compound was 89.16% by HPLC. IR showed that there were four significant peaks at 1160cm-1,1450cm-1,1380cm-1 and 1700cm-1. It was suggested that the molecular weight of the fraction V was 414 and it had a structure of steroids by the MS technique. The spectrum showed that the acaricidal active substance isolated from Mentha piperita extracts wasβ-sitosterol by any probility. 3.Effects of Mentha piperita extracts on activities of several enzymes of Tetranychus cinnabarinus In order to ensure the mechanism of acaricidal activity of Mentha piperita extracts against Tetranychus cinnabarinus, the adult spider mites were treated by 2mg/ml agents eluted fraction V in vitro, and the resulting acaricidal symptom and ultrastructure were investigated. Furthermore, the effect of treatment on the enzymes of monoamine oxidase (MAO), glutathione-S-transferase (GSTs), acetylcholine esterase (AchE) and proteinase in the mites was also studied. The results illustrated that the toxic symptom of the mites had experienced a significant differences after treatments, including four phases namely quiescence, activity, convulsion and death. The ultrastructural observation by the electronic microscope indicated that the control had a intact subcelluar structure (Original magnification,x5000;Original magnification,×10000), while the treatment was damaged severely (Original magnification,×20000). The enzyme activities of spider mites varied after being treated with Mentha piperita extracts, the monoamine oxidase (MAO) activity was boosted up, especially at the time of 12h and 24h after treatment(p<0.05); Difference was detected in the GSTs activities compared with control. The vibration of the GSTs activity was similar to that of the control indicating that the GSTs was in dynamic after treated with eluted fraction V. The GSTs activity was also intrigued with a trend of rising after treatment (the treated period of 4-24h), which demonstrated that the poisonous component had aroused the detoxification of T.cinnabarinus. Meantime, the acetylcholine esterase (AchE) and proteinase activity were inhibited induced by Mentha piperita extracts. It was implyed that the transfer of nerve impulse was possibly interdicted and the digestive system was maladjusted.
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