Insecticidal Activity of Ethanolic Leaf Extracts against the Maize Weevil, sitophilus zeamais Motsch (Coleoptera: Curculionidae)

Abstract

Laboratory studies were conducted in order to evaluate the toxicity of ethanolic leaf extracts of Euphorbia balsamifera Aiton, Lawsonia inermis L., Mitracarpus hirtus (L.) DC and Senna obtusifolia L. against Sitophilus zeamais Motsch. Ten 7 day old S. zeamais were released in 20g of disinfested sorghum grains treated with ethanolic extracts of the botanicals in plastic bottles at different concentrations of 2.5, 5.0 and 10.0x10 4 ppm at 30°C and 70% RH. Adult mortalities and lethal concentrations that killed 50% (LC 50) of the weevils' population at 24 Hours After Treatment (HAT) were determined. Concentration of body protein as well as inhibition rate of Acetylcholinesterase (AChE) activity in S. zeamais exposed to sorghum treated with the botanical extracts were also investigated. Results showed that the adult mortality ranged from 82.50 ± 2.50 to 100.00 ± 0.00% within 3 Days After Treatment (DAT). L. inermis had the highest LC 50 value (1.72 x 10 4 ppm), while E. balsamifera had the lowest (1.12 x 10 4 ppm). Biochemical tests showed that the botanicals reduced body protein and inhibited the activity of Acetylcholinesterase (AChE) in S. zeamais. The botanicals were found to be toxic to adult S. zeamais and therefore could be utilized to reduce the weevils' infestations in sorghum grains.