Lee_2026_Ecotoxicol.Environ.Saf_323_120796

Haemaphysalis longicornis, an ixodid vector associated with severe fever with thrombocytopenia syndrome, remains an important target for vector-control. Screening of Alpinia oxyphylla fruit essential oil identified nootkatone as the principal constituent associated with nymphicidal activity. Purified nootkatone showed activity against H. longicornis nymphs, with an LC(50) of 0.058 microg/cm(2). NTN3 and NTN3 plus piperonyl butoxide (PBO) yielded numerically lower LC(50) values of 0.034 and 0.026 microg/cm(2), respectively; however, because no formal LC(50) comparison or interaction analysis was performed, these values were interpreted only as descriptive shifts in apparent potency. To characterize exposure-associated biochemical responses, AChE activity, detoxification-related enzyme activities, PBO-associated LC(50) shifts, and molecular docking predictions were examined. In vitro nootkatone exposure reduced acetylcholinesterase (AChE) activity by 39.0-80.9% across the tested concentrations, while LC(50) exposure was associated with a 48.0% reduction in AChE activity. These findings indicate an association between nootkatone exposure and reduced AChE activity but do not establish a causal role in mortality. 7-Eethoxycoumarin O-deethylation (ECOD) activity increased by 15.4% after nootkatone exposure, whereas glutathione S-transferase (GST) and alpha/beta-esterase activities were not altered. Because ECOD is a general CYP450-linked proxy assay, this increase indicates altered monooxygenase activity rather than nootkatone-specific detoxification. PBO pre-exposure reduced ECOD activity and was accompanied by numerically lower LC(50) estimates, but these parallel responses alone, without formal mediation analysis, do not demonstrate that ECOD inhibition caused the LC(50) shift. Nootkatone is a promising vector-control candidate against H. longicornis nymphs, although causal mechanisms, environmental safety, and field applicability require further evaluation.