Toxicities of Eucalyptus dives Oil, 3-Carvomenthenone, and Its Analogues against Stored-Product Insects

The insecticidal toxicities of essential oils and other active components extracted from Eucalyptus dives leaves (as well as structural analogues) were studied against stored-product insects, Plodia interpunctella and Tribolium castaneum. 3-Carvomenthenone was purified from E. dives oil, and the structures were elucidated by electron ionization mass spectra, H-1-nuclear magnetic resonance (NMR), C-13-NMR, heteronuclear multiple quantum coherence, H-1-H-1 correlation spectroscopy, and distortionless enhancement by polarization transfer NMR. Using the fumigant method against P. interpunctella larvae and adults, cyclohexenone exhibited the strongest toxicity (50% lethal dose [LD50] against larvae and adults, 2.45 and 3.63 mu g/cm(3)), followed by methylcyclohexenone (2.95 and 4.24 mu g/cm(3)), seudenone (3.02 and 4.44 mu g/cm(3)), and 3-carvomenthenone (52.4 and 68.7 mu g/cm(3)). Using the contact method, cyclohexenone (LD50 against larvae and adults, 17.25 and 19.35 mu g/cm(2)) exhibited the most potent toxicities against T. castaneum larvae and adults, followed by methylcyclohexenone, seudenone, and 3-carvomenthenone. No functional radical on the backbone (2-cyclohexen-1-one) was more toxic than other chemicals. Structureactivity relationships between 3-carvomenthenone analogues and toxicities indicated that the toxicity of 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone might be conferred through the dermal organs of T. castaneum and P. interpunctella. This study indicates that E. dives oil, 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone have potential as natural agents to control stored-product insects.