Optimization of the insecticidal effect of essential oils of three medicinal plants against rice weevil Sitophilus oryzae L. (Coleoptera: Curculionidae)
International Journal of Agronomy and Agricultural Research (IJAAR), Vol. 7 (No. 2):
p. 55-63 (August 2015)Abstract
This study was carried out to find the best combinations amongst essential oils of three medicinal plants, Vepris heterophylla (Rutaceae), Hyptis spicigera (Lamiaceae) and Ocimum canum (Lamiaceae) against Sitophilus oryzae (Coleoptera: Curculionidae ) . Eight concentrations of essential oils (from 31 ppm to 669 ppm) were used for contact toxicity with five replications. Mortality was recorded after 24 hours. The LC5 and the LC100 of each essential oil were determinated. These values were used as boundaries of the experimental matrices 23 and 22 which were used to determine the maximum synergetic effect of combinations of essential oils. It was found that the essential oil of O. canum was the most efficient (LC100 = 68ppm) while V. heterophylla essential oil was the least efficient one (LC100 = 669 ppm). According to the combinations, it was found that the mixture of the three essential oils at their LC5 level induced 87.5% of mortality whereas the expected mortality was 5 %. The mixture of the three efficient doses (LC100) induced 95% of mortality although 100% mortality was the awaited. Optimum synergetic effect occurred when essential oil of H. spicigera is found in low proportion in the mixture. In order to valorise V. heterophylla and to reduce overexploitation of O. canum or H. spicigera, farmers could used them in combination as potent insecticides to reduce weevil attack of stored rice and sorghum. Get more articles at: http://www.innspub.net/volume-7-number-2-august-2015-ijaar/