Entomocidal activity of some plant extracts against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Entomocidal activity of ethanolic leaf extracts of four plant species namely Euphorbia balsamifera Aiton, Lawsonia inermis L., Mitracarpus hirtus (L.) DC. and Senna obtusifolia L. were evaluated in order to assess their protectant ability to stored sorghum against Sitophilus zeamais Motsch. The botanicals were applied to 20 g of sorghum grains at the rate of 25, 50 and 100 mgml-1, while no extracts was added to the control. Percentage repellency was recorded at 24 h after exposure (HAE) while adult mortalities of the weevils were obtained at 3 days after treatment (DAT). Adult emergence and grain perforations were recorded at 49 and 84 DAT, respectively. Repellency levels of the botanicals against S. zeamais ranged from 87.05 ± 0.45 to 100.00 ± 0.00%. Also, the ethanolic extracts resulted in high adult mortalities of the weevils in the treated sorghum grains. No adult emergence was recorded in grains treated with the botanical extracts. Highest (10.00 ± 2.04%) grain perforations among the treatments were observed in 25 mgml-1 of S. obtusifolia, while 2.50 ± 1.25% was the least in the highest concentration of E. balsamifera. Findings of the study have revealed that the selected botanicals could serve as stored sorghum protectants against S. zeamais infestations. Key words: Adult mortality, adult emergence, grain perforations, plant extracts, repellency levels, Sitophilus zeamais.