Acaricidal Activity of Ethyl Palmitate against Tetranychus cinnabarinus

Isolation and identification of bioactive compounds from medicinal plant of Inula flower is a potential approach for the development of new pesticides against the mite of Tetranychus cinnabarinus. Dry Inula Flower was used as the starting material to obtain active substances with acaricidal activity by organic solvent extraction and bioactivity assay verification. The main component of the active substances in fraction 33 was further identified by GC/MS and proven to be ethyl palmitate. In order to clarify the roles of ethyl palmitate playing against mites of Tetranychus cinnabarinus, the enzymatic activities were assayed regarding to four essential enzymes in the process of either nerve conduction or anti-oxidation reaction of the mites, including assays for Ca2+-ATPase, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). In addition, the substructures of the ethyl palmitate treated adult female mite of T. cinnabarinus were observed by transmission electron microscopy. In the bioassay, ethyl palmitae showed strong activities against the mites with the corrected mortality rates of more than 90% for samples at 2mg/ml concentration. The activity increases of antioxidant enzymes indicate a certain degree of stimulation of the anti-oxidant mechanisms to response for the ethyl palmitate treatment in vivo. The Ca2+-ATPase plays essential role in the maintenance of nerve cell excitability and conduction. Its enzymatic activity was subject to a certain degree of declination, which might cause the death of the mites due to suppression in nerve conduction. The toxicity effect of the mites by ethyl palmitate was further confirmed by TEM observation. The significant destruction of the skin structures and cellular substructures can directly affect the normal function of the cells, and ultimately lead to the death of the mites. Based on the strong acaricidal activity of ethyl palmitate has against the carmine spider mite, it is valuable to be further investigated for a new type of botanical pesticides development.