Evaluation of five medicinal plants for the management of Sitophilus oryzae in stored rice and identification of insecticidal compound

Sitophilus oryzae is a kind of stored grain pest. This is controlled by using natural pesticides, which are more reliable, cost-effective, biodegradable, and eco-friendly than synthetic pesticides. Several plants show different insecticidal activities against various pests on their different parts (leaves, seeds, etc.). In this study, methanolic extracts of Lantana camara (leaves), Carica papaya (seeds), Ricinus communis (leaves), Calotropis gigantea (flowers), and Gliciridia sepium (leaves) were used to identify the best insecticidal activity against the rice weevil by doing mortality tests for one week with four replications under laboratory conditions. Gliciridia sepium leaves showed the highest insecticidal activity (100 +/- 0) after seven days, and its extract was fractionated by using column chromatography and yielded 12 fractions. A contact bioassay of each fraction was performed, and fraction -11 showed the highest insecticidal activity against Sitophilus oryzae with a 100 % mortality after four days. Fraction -11 was analyzed by using GC -MS and FT-IR. Results revealed that the major constituent identified in fraction -11 was 4-C-methyl-myo-inositol. Therefore, 4-C-methyl-myo-inositol acts as a natural insecticide against rice weevils.