Efficacy of the ethanol extracts of the leaves of some plant species on the mortality of maize weevils, Sitophilus zeamais (Curculionidae: Coleoptera) and prevention of grain damage

Abstract

Sitophilus zeamais (maize weevil) damages maize, a major cereal crop in Ethiopia. A study was conducted to determine the anti-weevil activities of ethanol extracts of leaves of Juniperus procera, Phytolacca dodecandra, Ostegia integrifolia, Sansevieria trifasciata, and Eucalyptus globulus. Extraction was done using 70% ethanol. Two types of tests (toxicity and efficacy) were conducted using three doses, i.e., 50, 75, and 100 ml/kg of each plant. In the toxicity test, weevil mortality was measured at the 6th, 12th, 24th, 48th, and 72nd hours, then weekly for five weeks. For efficacy test, weevil mortality and grain damage (weight loss, percent holes, and percent germination) were assessed three months after treatment. J. procera and P. dodecandra were more toxic (96.6% and 96.4% mortality rate, respectively). The 50 and 75 ml/kg doses of E. globulus, 75 and 100 ml/kg doses of J. procera, of P. dodecandra, and of S. trifasciata killed 100% of the weevils; in the control mortality was 23.3%. Grain weight loss was high in the control (7.8%) followed by grains treated by 75 ml/kg extracts of O. integrifolia (5.9%). Percentage holes was high in the control (70%) followed by 75 ml/kg extracts of O. integrifolia (26.7%). Germination was high in grains treated with 50 and 75 ml/kg doses of J. procera, E. globulus, S. trifasciata, and P. dodecandra in descending order. The 75 and 100 ml/kg extracts of J. procera, E. globulus, S. trifasciata, and P. dodecandra were good candidates in the control of maize weevils with limitations of allelopathy in the 100 ml/kg. Keywords: Juniperus procera; Maize weevil; Ostegia integrifolia; Phytolacca dodecandra; Sansevieria trifasciata; Sitophilus zeamais.