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Liothrips wasabiae Haga and Okajima (Thysanoptera: Phlaeothripidae) was previously found only on field-cultivated wasabi (Eutrema japonicum) in the Chugoku region ( west Honshu, Japan) . However, it was found on water-cultivated wasabi in Shizuoka Prefecture (central Honshu, Japan) in 2016, where wasabi is cultivated in terraced fields with high humidity saturated by mountain streams. Unlike fieldcultivated wasabi, sprayed insecticide on water-cultivated wasabi is susceptible to dilution due to the high humidity and mist. Therefore, we conducted an experiment to determine the lethal effects of three neonicotinoid insecticides on adult and larval L. wasabiae at concentrations below the normal dilution, since both the adult and larval insects usually occur concurrently. The three neonicotinoid insecticides registered to the insect are dinotefuran, nitenpyram, and imidacloprid. The results revealed that dinotefuran and nitenpyram demonstrated greater insecticidal activities against both the adult and larval L. wasabiae than imidacloprid; however, all three insecticides, when used in lower concentrations than normal, proved less effective. This indicates that dinotefuran and nitenpyram may be used when sprayed insecticide is likely to be diluted, such as in water wasabi fields, even when both adult and larval insects occur simultaneously, taking into consideration the reduced insecticidal effect. [ABSTRACT FROM AUTHOR]