Evaluation of Plant Essential Oils against Sitophilus oryzae Linnaeus (Coleoptera: Curculionidae) under Laboratory Conditions

Abstract

Sitophilus oryzae Linnaeus, commonly known as rice weevil is a globally serious pest of stored grains, especially rice. Considering the target specific nature of botanicals and less hazardous effect than synthetic insecticides, the study was conducted to evaluate the effectiveness and appropriate dosage of four essential oils i.e., lemongrass (Cymbopogon citratus Stap.), eucalyptus (Eucalyptus globulus Labill.), peppermint (Mentha piperita L.), and tea tree (Melaleuca alternifolia L.) against S. oryzae. Each essential oil was used at 0.1, 0.5, and 1.0 ml doses on filter paper. A long glass cylinder (1000 ml size), divided into three (A, B, and C) sections, supplied with 20 g rice at ends, was used in the study. Ten freshly emerged adults of S. oryzae were released in the center of B, whereas treated and untreated filter paper was placed at A and C section, respectively. Observations on repellency and mortality percentage were recorded after 24 and 48 hours of exposure. The results indicated that all the tested essential oils exhibited insecticidal potential against S. oryzae. The insecticidal activity of all the essential oils increased with their application dose and exposure timing. Maximum mortality of S. oryzae after 48 hours was recorded in tea tree (76.67±3.33%) at 1.0 ml dose, whereas maximum repellency was recorded with 0.1 ml lemongrass (76.67±12.02%) treatment. Overall, tea tree and lemongrass showed maximum insecticidal performance, whereas peppermint was the least effective. After 48 hours, the lowest [0.008 ml (0.001-0.019) and highest [0.018 ml (0.000-0.078) LD50 values against S. oryzae were recorded with lemongrass and peppermint essential oils, respectively. The LD50 values recorded for eucalyptus and tea tree treatment were 0.07 ml (0.000-0.059) and 0.009 ml (0.000-0.046), respectively. Therefore, it is suggested that the essential oils of either tea tree or lemongrass may be applied in the warehouses against S. oryzae, that may not only cause repellency but also mortality among them.