Botanical oils as eco-friendly alternatives for controlling the rice weevil Sitophilus oryzae
Saad, A. S. A., Elsayed H. M. Tayeb and Houria L. Metraw
The rice weevil Sitophilus oryzae is a major stored grain pest infesting many grains in storage mainly wheat, rice and maize. Toxic effects of certain extracted botanical essential oils (EOs) were evaluated against the adults of Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae). Bioassays were carried out by fumigation and guide tables were presented to show the effective range of concentrations of each of the evaluated essential oils and their corresponding mean number of responded insects. The essential oil of fennel (seeds) (Foeniculum vulgare) did not show any toxic effect up to the concentration of 300 µl/370 ml air and Common Sage (Marmaria leaves) (Salvia officinalis) up to 250 µl/370 ml air during the first 48 hrs then they showed a very weak effect. The essential oil of spearmint leaves (Mentha spicata L.) was the utmost toxic and had a lowest LC50s calculated by 4.43, 3.88 and 3.27 µl/370 ml air after different exposure periods of 24, 48 and 72 hrs, respectively, followed by the essential oil of clove (Syzygium aromaticum) (382.62, 79.95 and 9.23 µl/370 ml air, in respect). In this concern, clove showed its higher toxicity after 72 hrs. The mortality of the exposed adults to EOs increased with the increase of concentrations and time of exposure to each one. The calculated values of toxicity index showed that the essential oil of mint was the most toxic EO (100%) followed by clove (35.43%). Moreover, log (dose)/N.E.D. (response) (Ld-p) regression lines for certain bio assayed botanical essential oils against S. oryzae were also illustrated. Therefore, it could be recommended that the essential oils of spearmint leaves and clove buds could be used to control the rice weevil, S. oryzae.
Keywords: Botanical oils; Sitophilus oryzae; Guide tables; LC50; Toxicity index; Ld-p lines