Haemaphysalis longicornis acetylcholinesterases are triggered by the repellent effect of cinnamaldehyde, a primary compound found in cinnamon oil

The control and prevention of ticks and tick-borne diseases rely on chemical insecticides and repellents. Plant-derived compounds potentially represent new and safer repellents. Cinnamaldehyde, a component of cinnamon oil, exhibits antibacterial, anti-inflammatory, acaricidal, and repellent activity against ticks. Here we studied the molecular mechanism of the repellent effects of cinnamaldehyde on ticks. A 2% cinnamaldehyde treatment resulted in more than 90% nymph repellency within 6 h. Nymphs were exposed to cinnamaldehyde for 30 min, and subsequent transcriptome and metabolome analyses revealed the involvement of Haemaphysalis longicornis Acetylcholinesterases (HL-AchEs) in the response process. HL-AchEs was transcribed in all tick developmental stages and tissues. Following cinnamaldehyde treatment, the transcript and specific activity of the enzyme of AchE were significantly altered. Following RNAi, electroantennography (EAG) tests demonstrated a significant decrease in response to various repellents as well as a significant decrease in repellency. Our findings have revealed that HL-AchEs mediates cinnamaldehyde-induced tick repellency, and the results provide insights into the mechanism of plant-derived tick repellents.