| Phytophagous mite is one of most serious pest of wide range of field and forest, causing economic losses, that seriously restricts the production and development of agroforestry in our country. Owing to their small individual, high reproductive potential, short life cycle and the useful of chemical pesticides to control them, result in the "3R" For its prevention has become one of the urgent problems of current agricultural production. Botanical acaricide derived from plants also may be safety for human being and livestock, environment and natural enemies, meeting the demand of the sustainable development of agriculture, has become a popular tendency of the development new acaricide in recent years.Lactuca sativa L., commonly known as lettuce, belong to the compositae family, annual or raw herbs for two years. In the study, we used different solvents to extract the active substances of lettuce roots, leaves and seeds, and screened out the extracts with highest activity against female adult of carmine spider mite, Tetranychus cinnabarinus, then bioassay-directeded fraction and isolated the extracts gave some active compound and identified their structure, and evaluated the acaricidal activities of those compounds. The main results were as follows:1Assessing the acaricidal activity of L. sativaUsing room temperature heat extraction, ultrasonic extraction, reflux extraction and microwave extraction method, harvest lettuce plants in July as the experimental material, to obtained extracts, room temperature extraction is determined finally, according to the differences in crude extract extraction rate, considering the needs of actual operation. Using petroleum ether(60-90℃), acetone and methanol parallel to extract lettuce roots, leaves and seeds,9crude extracts were obtained finally. The acaricidal activity against the female adult of T. cinnabarinus of these extracts were tested, by slide-dip bioassay. At the concentration of2.5mg/mL, the acetone extract of lettuce leaves exhibited the highest acaricidal activity, causing63.04%mortality at48h. Moreover, the toxicity of acetone extract from lettuce leaves in July and September were determined respectively, the result showed that the acetone extract of lettuce leaves in July had stronger acaricidal activity, with LC50value of1.429mg/mL.2The action modes of acetone extract of L. sativa leaves against T.cinnabarinusThe contact activities of acetone extract of lettuce leaves against larvaes, nymphs and eggs of T.cinnabarinus were tested. The result suggested that the extract showed moderate activity against each mite stage. After treatment48h, the LC50values of extract against nymphs and larvaes of T.cinnabarinus were0.569and0.196mg/mL, respectively. Also, extract has influence on egg hatching, at the concentration10mg/mL, the hatching rate was14.68%after treatment7d. Except that, it also had strong repellency activity against mites, at the concentration5mg/mL, the repellent rate against larvaes and nymphs remained above90%, and the repellent activities against adults were reducing with increasing time gradually, was61.11%after treatment48h. Moreover, the actone extracts of lettuce leaves had no obvious oviposition deterrent property against the female adults, at the concentration5mg/mL, the rate of oviposition inhibition was only46.60%.3Bioguided fractionation, purification and identification of active compounds extracted from L. sativaUsing silica gel column and thin layer chromatography, the acetone extract of lettuce leaves was isolated, and27fractions were obtained. Comparing the contact activity against T.cinnabarinus, at the concentration1mg/mL, the11th fraction showed the highest activity, and the mortality was93.47%, LC50was0.751mg/mL. The11th fraction was purified by solid-liquid extraction method, and methanol fraction and the residue fraction were got. In the test of acarcidal activity, the residue fraction presented better activity, with the value LC50of0.036mg/mL. The residue fraction further was purified by repeated column chromatography, and the5subfractions separated from the residue fraction, among which11-b subfraction possessed the highest activity,11-a subfraction was next, their mortality were89.00%and69.35%at48h, respectively.After recrystallization for the11-a subfraction, white needle crystal was obtained. Through the analysis of qualitative test, LC/MS, NMR spectrum and comparison with library spectra, the crystal was β-sitosterol. The compound in11-b couldn’t been got, because that it occured decomposition in the process of purification.4Evaluation of the bioactivity of compoundThe biological activity of β-sitosterol isolated from L. saliva against T. urticae. T. cinnabarinus and Panonychus citri were determined. The result showed that the compound had efficient contact-kill activity, but its repellent and oviposition deterrent activity were not significant, did not have egg hatching inhibition effect. After treatment48h, the LC50value of β-sitosterol against female adults, nymphs and larvaes of T.cinnabarinus were0.315,0.370and0.419mg/mL. respectively, and the value of it against female adults of T. urticae and P. citri were0.380and0.545mg/mL. The repellency activity against female adults of T. cinnabarinus was reducing with time increasing, and the trendency was obvious. After treatment12h, the repellency rate of each concentration were all grade Ⅲ, after24h, the repellency rate was remained grade Ⅲ at the concentration1mg/mL. Moreover,β-sitosterol showed slight ovicidal activity, at the concentrate4mg/mL. eggs’hatching rate was88.63%. The oviposition inhibitory activity of the compound was unstable, at the concentrate0.5and0.25mg/mL, the trend change was volatile, but they both had no obvious inhibition activities. |
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