Authors : T.S.L. Ngamo , I. Ngatanko , M.B. Ngassou , P.M. Mapongmestsem and T. Hance
Abstract: To prevent attacks of stored grains by insects pest, rural farmers in the past times, regularly introduce aromatic plants in their granaries. These plants were used alone or associated in groups of 2 or 3 plants. Active compounds of these aromatic plants, mostly present in their essential oils have insecticidal properties. In the present work, crude essential oils of some Lamiaceae, as Hyptis spicigera (Lam.) Ocimum canum (Sims) and Plectranthus glandulosus (Hook); of Rutaceae Vepris heterophylla (Letouzey) and finally of Astareceae Echinops giganteus (Adams) were applied both alone and in balanced combinations on the adults of stored grain pest Sitophilus oryzae (L.) (Coleoptera: Curculionidae) to evaluate their toxicity. These experiments show that all tested essential oils are insecticide except that of E. giganteus. Applied alone, their LD50 vary from 42.91 ppm for the oil of O. canum to 349.8 ppm for oil of V. heterophylla. Applied in balanced combination O. canum and H. spicigera expresses no difference (p<0.05) between observed (75.83 ppm) and expected (77.46 ppm) LD50. E. giganteus which was without any insecticidal efficiency synergise the essential oil already active. Moreover, of 20% O. canum in 80% of E.giganteus leads to 100% of mortality. While combined in this same proportion O. canum and P. glandulosus oils also express synergy. V. heterophylla, relatively rich in oxygenated sesquiterpenes increases values of the observed LD50 higher and significantly different (p<0.05) from the expected values.
T.S.L. Ngamo , I. Ngatanko , M.B. Ngassou , P.M. Mapongmestsem and T. Hance , 2007. Insecticidal Efficiency of Essential Oils of 5 Aromatic Plants Tested Both Alone and in Combination Towards Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Research Journal of Biological Sciences, 2: 75-80.