OBJECTIVE  To prepare tea tree oil into microcapsules emulsion, evaluate its repellent effects on leeches and clarify the repellent mechanisms.

  METHODS  Tea tree oil aqueous solution was prepared with Tween 20 as solubilizer. Span 80 was used as the emulsifier to prepare tea oil emulsion. Gelatin and sodium alginate were used by complex coacervation method to prepare tea tree oil microcapsules. The particle size, morphology and the binding mode of microcapsules were characterized. The tea tree oil microcapsules emulsion was obtained by dispersing the microcapsules into the tea tree oil emulsion. The filter-paper ring method and the repellent test in water were used to evaluate the repellent effects and time of the tea tree oil microcapsules emulsion, tea oil aqueous solution, blank microcapsules emulsion and the positive drugs on leeches. The activities of acetylcholinesterase (AchE), glutathione S-transferase (GST) and carboxylesterase (CarE) activities in vivo were measured to clarify the repellent mechanisms of tea tree oil microcapsules emulsion on leeches.

  RESULTS  The optimal ratio of gelatin and sodium alginate with high coacervation yield was obtained. The microcapsules with uniform particle size, uneven size and high encapsulation efficiency were successfully prepared. According to the orthogonal design, the optimal formulation was obtained, and the tea tree oil microcapsules emulsion was uniformly dispersed and stable. The microcapsules emulsion could effectively repel leeches and prolong the repelling time. It was clarified that tea tree oil microcapsules emulsion played a repellent role by increasing AchE activity and inhibiting GST and CarE activities in vivo.

  CONCLUSION  The prepared tea tree oil microcapsules emulsion can avoid the volatilization of tea tree oil, which can prolong the repelling time. In summary, this study provides a new idea for the development of natural essential oil as the repellents with broad market prospects.