Bioinsecticidal activity of Vitex negundo L. (Family: Verbenaceae) leaf extracts against Sitophilus granarius L. in stored maize grains

Abstract

The insecticidal property of dry leaves of Vitex negundo against the Sitophilus granarius in the laboratory at (28±3) 0C and (78±3) % r. h. with Soxhlet extracted extracts of V. negundo leaves in ethanol, methanol, chloroform, acetone and n-Hexane were tested and found very effective to control the store grain insect pest. The biopesticidal effects of extracts in different solvents were compared by calculating LD10, LD50, LD90 and LD99 values for 96 hrs. The Probit analysis of data demonstrated that LD values for ethanol, methanol, chloroform, acetone and n-Hexane extracts were LD10 – 1.216, 1.141, 0.9298, 1.265, 0.5398 ml/Kg; LD50 – 2.997, 3.106, 2.490, 3.727, 1.302 ml/Kg; LD90 – 7.392, 8.457, 6.667, 10.98, 3.142 ml/Kg and LD99 –15.43, 19.14, 14.88, 26.50, 6.439 ml/Kg respectively, for 96 hrs. These results demonstrated that the mortality increased with increase in concentration of extract and exposure time. There was nearly zero fecundity and next generation was not observed in treated grains. The extracts of V. negundo leaf may be of high value in grain storage against S. granarius, especially in subsistence agriculture where the plants are locally available to local farmers. Hence, we conclude that the ethanol, chloroform and n-Hexane extracts from V. negundo leaf are more effective and useful. It served as being a potential insecticidal agent and could be applicable to the management of populations of stored-product insects particularly against the infestation by granary weevil, S. granarius after proper dose formulation.