Biochemical and molecular mechanisms involved in the response of Haemaphysalis longicornis (Acari: Ixodidae) to Cinnamomum cassia essential oil and its major constituent

To develop an appropriate program for essential oils (EOs) used in pest control, it is important to acquire information about the effect of the EO when used at a low concentration. Previously, we demonstrated the enzymatic activity of Haemaphysalis longicornis (the main livestock pest in Australia and New Zealand) exposed to Cinnamomum cassia EO and (E)-cinnamaldehyde (its major compound) when applied at 50% lethal concentration (LC50). However, H. longicornis respond to toxic substances via different mechanisms and at different times of exposure. Herein, the enzymes involved in the defense response were studied by monitoring glutathione-S-transferase, acetylcholinesterase, and Na+/K+-adenosine triphosphatases (ATPase) activities in H. longicornis larvae exposed to C. cassia EO and (E)-cinnamaldehyde across different times. Further, the molecular changes related to the defense mechanisms were studied by monitoring adenosine triphosphate (ATP)-binding cassette (ABCB10) gene expression. In addition, we investigated the acaricidal activity of the test substances against the engorged larvae and nymphs of H. longicornis. Our results showed that the activities of these enzymes were significantly affected by the EO and/or (E)-cinnamaldehyde depending on the exposure time. We observed up-regulation of the ABCB10 gene in the larvae. Also, our results revealed that C. cassia EO (LC50 = 1.46 and 16.69 mg/mL) and (E)-cinnamaldehyde (LC50 = 3.86 and 17.96 mg/mL) were effective against the engorged larvae and nymphs, respectively. Our results provided a deeper understanding of the defense mechanisms of H. longicornis, which may provide an important clue for the development of EO-based acaricides that are cheaper and environmentally friendly.