Abstract: Terpinen-4-ol is the main insecticidal composition in essential oil of Sabina vulgaris Ant.，an insecticidal plant. The toxicity, poisoning symptoms and biochemical effects of terpinen-4-ol on larvae of the oriental armyworm, My thimna separata (Walker) were assayed. The results showed that terpinen-4-ol was very toxic to 3-instar larvae of the armyworm with fumigating application (LC₅₀=5.3473 μL·L^-1)and the LD₅₀ of contact activity to-4-instars larvae of the armyworm was 147.8 μg/larvae. The poisoning symptom caused by the compound could be divided into4-stages, i.e., excitation, convulsion, paralysis and death; but some paralyzed insects could recover. In vivo, the activity of Na⁺,K⁺-ATPase in brain of 5th instar larvae tested was inhibited; the inhibition ratio was 21.28% in exciting stage, 25.62% in convulsing stage, 32.10% in paralysis stage, and 34.92% in recovering stage, respectively. In vitro, the I₅₀ of Na⁺,K⁺-ATPase was 133.75 μg·mL^-1(Y=2.2236+1.3058X r=0.988, χ² =1.26). It had certain influence on the activity of AChE. In the excitation stage, the activity of ester enzyme of the treated larvae was 77.0% of that of the control; in the paralysis stage, it was 1.33 times; but it was as high as that of the control in the recovery stage.

Key words: Terpinen-4-ol, insecticidal activity, Mythimna separata, Na⁺, K⁺-ATPase-AChE