Screening of essential oils with acaricidal activity against Haemaphysalis longicornis (Acari: Ixodidae) and analysis of active components

Haemaphysalis longicornis (Acari: Ixodidae) is an important vector of numerous pathogens and poses a great threat to veterinary and public health. Commercially available tick repellents are extensively used and primarily comprise synthetic molecules; however, there are concerns over their safety and environmental impacts. Biologically based acaricides, particularly the plant-derived essential oils (EOs), may constitute an appealing alternative. We screened 20 different EOs by packet tests of unfed H. longicornis nymphs, and found that EOs of cinnamon, clove and chamomile were the most toxic (mortality > 80 %). Cinnamon EO had the most competitive acaricidal activity, with lethal concentration 50 (LC50 ) rates of 0.4530 %, 0.2316 % and 0.0342 % (v/v) for unfed adults, nymphs and larvae, respectively. Furthermore, 5.00 % (v/v) cinnamon EO showed reproductive inhibition against H. longicornis, with significantly higher rates of oviposition reduction (53.19 %) and hatching reduction (46.21 %) compared with the negative control group. Composition analysis of cinnamon EO by gas chromatography-mass spectrometry (GC-MS) revealed that the major chemical compounds were transcinnamaldehyde (72.21 %) and cinnamic acid (19.45 %), with the former showing similar levels of acaricidal activity and oviposition inhibition as cinnamon EO. This study has demonstrated the potential of cinnamon EO and trans-cinnamaldehyde as natural acaricides against H. longicornis, and is the first to characterize their oviposition inhibition activity.