Acaricidal and repellent activities of Litsea cubeba (Lour.) oil and 3,7-dimethyl-2,6-octadienal against Haemaphysalis longicornis (Acari: Ixodidae)

The bioactivity of the essential oil extracted from Litsea cubeba fruits against tick vectors of severe fever with thrombocytopenia syndrome is unknown. In this study, L. cubeba oil and its main constituents, 3,7-dimethyl-2,6-octadienal and its similar structures, were evaluated for their acaricidal and repellent activities on the unfed nymphs and adults of Haemaphysalis longicornis. L. cubeba oil displayed both acaricidal and repellent activities against both life stages. Among the constituents of L. cubeba oil, only 3,7-dimethyl-2,6-octadienal exhibited both acaricidal and repellent activities against both life stages. In a repellent bioassay, 3,7-dimethyl-2,6-octadienal and L. cubeba oil at dose of 0.08 mg/cm² provided excellent repellence (100%) against the nymphs and adults for over 60 min post-application. When the acaricidal and repellent activities of 3,7-dimethyl-2,6-octadienal and its similar structures were compared, activities of all tested derivatives were significantly less potent than those of 3,7-dimethyl-2,6-octadienal. The strong acaricidal and repellent activities of 3,7-dimethyl-2,6-octadienal in L. cubeba oil suggests that it is a promising natural candidate for developing new sustainable acaricidal and repellent agents.