Efficacy of organic extracts of Nicotiana tabacum (Solanaceae) leaf and Jatropha curcas (Euphorbiaceae) seed against Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) under laboratory conditions

Abstract

The maize weevil is a pest of stored maize controlled with synthetic insecticides. The widespread use of these insecticides, however, is harmful to the environment and human health. In this study, solvent extracts (SEs) and powder treatments (PTs) of Nicotiana tabacum leaves and Jatropha curcas seeds were tested for their efficacy against Sitophilus zeamais Motschulsky. The experiment was designed in a completely randomized design with three replications. For extraction, ethyl acetate and dichloromethane were used. Extract concentrations of 25, 50, 75 and 100% were evaluated at dosages of 4, 8, and 12 ml. PT of botanicals was evaluated at dosages of 4, 8, and 12 g. Mortality was calculated at 1, 3, 5, 7, and 14 days after treatment. At the end of the experiment, the percentage of grain damage, weight loss, and germination percentage was calculated. Dichloromethane SEs of N. tabacum leaves and J. curcas seeds at 50, 75, and 100% levels of extract concentrations (LEC) in all doses caused 100% mortality. The J. curcas seed PTs at 12 g and its SEs of ethyl acetate and dichloromethane in 100% LEC at 12 ml experienced the least grain weight loss of 1.36, 0.79 and 0.64%, respectively. The results suggest that these plant-based products are very promising, generally available, cost-effective, nontoxic to non-target organisms, and simple to produce. Thus, dichloromethane SEs of N. tabacum leaves and J. curcas seeds at 50% LEC and above in all doses can be recommended for the management of S. zeamais.