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Laboratory bioassays were conducted to characterize the acute toxicity of 7 monoterpenoids to tracheal mites, Acarapis woodi (Rennie), and their honey bee, Apis mellifera L., hosts. Citral, thymol, carvacrol, α-terpineol, pulegone, d-limonene, and menthol were applied as fumigants to mite-infested honey bees. Thymol and menthol were the most toxic compounds to honey bees, and α-terpineol was the least toxic. Menthol, citral, thymol, and carvacrol were more toxic to tracheal mites than to honey bees. Pulegone, d-limonene, and α-terpineol were more toxic to honey bees than to tracheal mites. Menthol was 18.9 times more toxic to tracheal mites than to honey bees at the LC 50 concentrations; however, as the concentration increased, bee mortality increased more rapidly than mite mortality, and menthol was only 5.7 times more toxic at the LC90 concentrations. Probit regressions for bee and mite mortality were parallel for citral and thymol. Citral and thymol were 2.9 (2.5-3.3) and 2.0 (1.0-3.6) times more toxic to tracheal mites, respectively, at all concentrations estimated.