Chemical Constituents and Insecticidal Activities of the Essential Oil from Amomum tsaoko against Two Stored-Product Insects

The aim of this research was to determine the chemical constituents and toxicities of the essential oil derived from Amomum tsaoko Crevost et Lemarie fruits against Tribolium castaneunz (Herbst) and Lasioderma serricorne (Fabricius). Essential oil of A. tsaoko was obtained from hydrodistillation and was investigated by gas chromatography-mass spectrometry (GC-MS). GC-MS analysis of the essential oil resulted in the identification of 43 components, of which eucalyptol (23.87%), limonene (22.77%), 2-isopropyltoluene (6.66%) and undecane (5.74%) were the major components. With a further isolation, two active constituents were obtained from the essential oil and identified as eucalyptol and limonene. The essential oil and the two isolated compounds exhibited potential insecticidal activities against two stored-product insects. Limonene showed pronounced contact toxicity against both insect species (LD50 = 14.97 mu g/adult for E castaneum; 13.66 mu g/adult for L. serricorne) and was more toxic than eucalyptol (LD50 = 18.83 mu g/adult for E castaneum; 15.58 mu g/adult for L. serricorne). The essential oil acting against the two species of insects showed LD50 values of 16.52 and 6.14 mu g/adult, respectively. Eucalyptol also possessed strong fumigant toxicity against both insect species (LC50 = 5.47 mg/L air for E castaneum; 5.18 mg/L air for L. serricorne) and was more toxic than limonene (LC50 = 6.21 mg/L air for T castaneum; 14.07 mg/L air for L. serricorne), while the crude essential oil acting against the two species of insects showed LC50 values of 5.85 and 8.70 mg/L air, respectively. These results suggested that the essential oil of A. tsaoko and the two compounds may be used in grain storage to combat insect pests.