Assessment the Contact Toxicity of Methyl Palmitate on the Carmine Spider Mite

Our previous studies showed that methyl palmitate had the acaricidal activity to T. viennensis. However, the mechanism of action of methyl palmitate on T. viennensis is unknown. Here, the toxicosis symptoms of T. viennensis exposed to methyl palmitate were studied to preliminarily uncover the acaricidal mechanism of methyl palmitate. Methyl palmitate caused dose-dependent mortality of T. viennensis in our studies. A moderate dose of methyl palmitate (5 mg/mL) initially elicited excite, and early oviposit without spinning. After a few hours, limb twitching was observed, and this was followed by a stage of depressed activity in about 5 hours. Subsequently, the mites developed a condition, which had the outward appearance of exosmosis on the back of the mites during the 15^th-20^th hr, and reduced eggs production. The mites eventually died in a few hours. Some typical neurotoxin symptoms such as excitement and convulsions were observed on the mites exposed to methyl palmitate. Methyl palmitate might be a type of neurotoxin. Compared to other neurotoxic insecticide, poisoning with methyl palmitate is slow in mites. Furthermore, the effects caused at sub cellular level by methyl palmitate were evaluated by transmission electron microscopy. Serious damage in ultra structure was observed at a concentration of methyl palmitate (5 mg/mL). Autolysis of membranous structure was observed, especially in mitochondria, which may imply a novel action of methyl palmitate.