The bio-efficacy of Calpurnia aurea against Sitophilus zeamais (Motschulsky) (Coleoptera; Curculionidae) of stored maize under laboratory condition in Ethiopia

Abstract

N-hexane (non-polar), chloroform (partial polar), distilled water, methanol, acetone and ethanol (polar) extracts (10 g/100, 20 g/100 and 20 g/100 ml extraction levels) and leaf powder of Calpurnia aurea were tested as protectant against maize weevil, Sitophilus zeamais on filter paper and in maize grains under laboratory condition. The extracts and powder were applied at rate of 2 and 3 ml on filter paper and at a rate of 5, 10 and 15% (w/w) on admixture bioassay. Parental adult's mortality, F1 progeny emergence, percent protection, percent grain damage and weight loss were measured as efficacy determining parameters. Polar solvent extracts of the C. aurea applied at all rates on filter paper from all levels of extraction induced significant (p < 0.05) toxicity effect compared to partial and non-polar solvent extracts, as well as the negative controls. Besides, hundred percent adult weevil's mortality was induced by all polar solvent extracts of C. aurea applied at rate of 3 ml per filter paper from 30 g/100 ml level of extraction 24 h after treatment application. Furthermore, the powder of C. aurea applied at all rates was also induced significantly good degree of protection of maize grains against F1 progeny emergence (≥ 78%), percent grain damage (≤ 4.00) and weight loss (≤0.50) by maize weevils in about 2 month's storage period. Therefore, leaf powder and the solvent extracts of C. aurea were potent and could be used for managing maize weevils on stored maize under farmer's storage conditions in Ethiopia.