Efficacy of castor bean oil (Ricinus communis L.) against maize weevils (Sitophilus zeamais Mots.) in northwestern Ethiopia

The maize weevil, Sitophilus zeamais Mots. (Coleoptera: Curculionidae), undermines food security. The biocidal activity of castor bean oil (Ricinus communis L.) against S. zeamais, was studied at various doses at Dembecha, northwestern Ethiopia in 2013/14 (November–April). In the castor bean oil efficacy test, weevil mortality steadily increased with castor bean oil dose. According to the results of the ANOVA, number of dead weevils significantly varied between castor bean oil doses 1 h after treatment (F10, 21 = 117.6, p < 0.0001). Just 53% of the weevils were killed in one hour by applying 2 ml of the oil while doses higher than 2 ml killed greater than 85% of the weevils. Using Probit analysis, the LD50 of using castor bean oil against maize weevils was calculated to be 2.04 ml. Therefore, 2 ml of castor bean oil was found sufficient to destroy 50% of the weevils. Higher doses of castor bean oil significantly reduced maize seed germination.