Abstract: 【Aim】 This research aims to evaluate the difference in insecticidal activity among the optical isomers and racemate of terpinen-4-ol against the housefly, Musca domestica, and to provide a guidance for utilization of terpinen-4-ol optical isomers. 【Methods】 The fumigation and knock-down toxicities of the optical isomers and racemate of terpinen-4-ol against 4-day-old adults of M. domestica were detected with the Erlenmeyer flask method, and the effects of these compounds onNa⁺, K⁺-ATPase specific activity in the head were tested. 【Results】 The racemate of terpinen-4-ol showed the highest fumigation and knockdown toxicities to M. domestica adults, followed by the dextroisomer and then the laevoisomer. The median lethal concentration (LC₅₀) values of the racemate, dextroisomer and laevoisomer against M. domestica adults were 2.5, 2.9 and 3.7 μL/L, respectively, and the median knockdown time (KT₅₀) values in treatment of LC_90were 12.6, 16.7 and 18.9 min, respectively. In vivo, the dextroisomer, laevoisomer and racemate of terpinen-4-ol could significantly inhibit Na⁺, K⁺-ATPase specific activity, and the inhibitory effect showed time effect, viz.the inhibition was enhanced as the symptom exacerbated; moreover, the laevoisomer showed more significantly inhibitory effect onNa⁺, K⁺-ATPase activity than the dextroisomer and racemate. In vitro, terpinen-4-ol inhibited Na⁺, K⁺-ATPase activity with a dosedependent effect, and racemate showed remarkably superior inhibitory effect than the dextroisomer and laevoisomer at the same dose. 【Conclusion】 There exist differences in insecticidal activity of the optical isomers of terpinen-4-ol against M. domestica adults, and the racemate has remarkably superior activity to the optical isomers. Thus, the mixture of the optical isomers of terpinen-4-ol should be adopted as the effective component to develop terpinen-4-ol insecticide.

Key words: Musca domestica, terpinen-4-ol, optical isomer, racemate, fumigation toxicity, knock-down toxicity