Chemical composition and insecticidal properties of Origanum glandulosum (Desf.) essential oil from Algeria

BACKGROUND: To find natural compounds with insecticidal properties which could be an alternative to synthetic insecticides, oregano essential oil was tested against the insect Rhizopertha dominica devastating stored cereals. RESULTS: Oregano oils were isolated by steam distillation, analysed by gas chromatography and gas chromatography-mass spectrometry and investigated for their insecticidal activities against Rhizopertha dominica. Contact and fumigant toxicities of global oil and three of its fractions recovered respectively after 2h and after 0-2.5, 2.5-5 and 5-10 min of extraction were tested using the filter paper method. Eighteen components, representing 92.6% of the oil, were identified. The major components were thymol (38.8%), carvacrol (32.9%), p-cymene (7.9%) and gamma-terpinene (5.1%). Toxicity tests showed that insect mortality increases with the concentration used (0.39%, 0.78%, 1.56%, 3.12% and 6.24%V). For all concentrations, the contact effect of global oil and fraction F-2 was better than the fumigant effect. Whereas fractions F-1 and F-3 were more toxic by fumigation for concentrations lower or equal to 1.56%. their contact effect was more significant for concentrations higher than 1.56%. CONCLUSION: These results suggest that oregano oil has important insecticidal properties and may be useful as a natural grain protectant against Rhizopertha dominica to replace synthetic insecticides. (c) 2008 Society of Chemical Industry.