Evaluation of the repellent effect of Dioscorea sansibarensis Pax (Dioscoreaceae) leaf essential oil against Bruchus chinensis Linnaeus, 1758 (Coleoptera: Bruchidae)

Abstract Laboratory experiments were conducted to determine the repellent activities of the ornamental plant Dioscorea sansibarensis leaf essential oil against the Bruchus chinensis bean weevil in the protection of stored legumes. The leaves exhibited potential repellency in a Y-tube olfactometer. The tabulated data show that 10µL of leaf oil exhibited a repellency of 41.33%, with a grouped median of 53.33%, which was better than 10 µL of Actellic 50 EC, which had a repellency of 36.00% and a grouped median of 40%. Statistically, there was no significant difference in the percentage repellency obtained from the leaf oil and Actellic 50 EC at different concentrations (10, 20, 30 and 40 µL/mL, X2(7, N=200) = 114.93, P< 0.05). The GC-MS analysis identified 16 compounds in the leaf oil. The main compounds and their percentage composition were phytol (19.46%), 1-epi-α-gurjunene (11.71%), palmitic acid (10.48%), ethyl palmitate (8.87%), methyl palmitate (7.72%), isophytol (5.99%), 2-heptadecanone (4.59%) and α-selinene (4.5%). The repellency caused by the by leaf oil may have been due to the presence of α-selinene, also known as naphthalene, 1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methylethenyl)-, [1S- (1.α.,7.α.,8a.α.)]-. Dioscorea sansibarensis may be a good choice for repellent formulations.