Acaricidal Activity of Methyl Palmitate to T. cinnabarinus

Methyl palmitate, a kind of fatty acid methyl ester, has been found in many plants. Many biological functions of methyl palmitate have been found. Recently we isolated the methyl palmitate from the green walnuts husks and found it has acaricidal activity that had not been reported before. Here, the acaricidal activity of methyl palmitate, industrial methyl palmitate and the mixtures of methyl palmitate and Silwet L-77 were studied respectively. The results showed that the LC₅₀ of methyl palmitate for female mites was 1.72 mg/ml and 7.73 mg/ml for eggs. The contact toxicity of methyl palmitate on female mites is better than on eggs. Methyl palmitate also has strong repellent effect on the female mites. Then the acaricidal activity of industrial methyl palmitate was studied, and the results showed that both of the mortality and adjusted mortality of Tetranychus cinnabarinus were more than 70% when the concentration of industrial methyl palmitate was 10 mg/ml and 8 mg/ml. In order to improve the acaricidal activity of industrial methyl palmitate, Silwet L-77, a kind of silicone surfactants, was used to mix with industrial methyl palmitate to increase the permeability of industrial methyl palmitate. The female mites were treated with nine kinds of mixture of industrial methyl palmitate and Silwet L-77. The results showed that the best mixture ratio of the industrial methyl palmitate and Silwet L-77 was 8 mg/mltimes200 ppm, 5 mg/mltimes400 ppm and 8 mg/mltimes400 ppm, and all the acaricidal activity of the three mixtures were more than 90%. The mixture ratio could be used in the production of methyl palmitate acaricides.