Potential of Olax zeylanica (Olacaceae) as a botanical insecticide for the control of the Maize Weevil Sitophilus zeamais Motschulsky

The possible use of leaf powder of Olax zeylanica in managing the maize weevil, Sitophilus zeamais was investigated in the present study. Mortality of one week old adults was obtained for five different doses each for their insecticidal effect (1.0, 2.0, 3.0, 5.0 and 7.5g) and fumigation toxic activity (2.0, 3.0, 5.0, 7.5, 10.0g) separately. In each bioassay, the mortality was recorded after 3, 6, 9, 12, 18 and 24 hours after they were exposed to different doses of the plant powder. The results of both bioassays revealed that the leaf powder of this plant elicited a very high insecticidal activity as well as fumigation toxic activity in S. zeamais weevils. Mortality effect of the powders on the weevils was found to be dose and time dependent. The observations indicated that the adult mortality increased with the increase of the exposure time and the dose. No mortality was observed 3 hours after the exposure of weevils to leaf powder at all doses. A high mortality rate was observed after 9 hours of exposure with all doses except for the lowest and a 100% mortality was recorded with 7.5g after 24 hours. Fumigation toxicity of plant powder against the weevils also gave similar results where no weevil deaths were observed at all doses of leaf powder after 3 hours of exposure. At the highest dose of 10.0g, 98% mortality was observed after 24 hours. The overall results imply the strong possibility of using leaves of Olax zeylanica as a potent bio-insecticide in protecting maize grains from S. zeamais infestations.