The maize weevil, Sitophilus zeamais Motschulsky, is a significant pest of stored maize worldwide, often controlled using contact insecticides or fumigants. However, due to issues such as toxic residues, human intoxications, and resistance, researchers have sought alternatives such as organic extracts. The present study aimed to evaluate the insecticidal properties of organic extracts Nicotiana tabacum (Solanaceae) leaves and Jatropha curcas (Euphorbiaceae) seeds against S. zeamais in laboratory settings. Dichloromethane (DCM) and Ethyl acetate (ETA) were used for extraction. Two types of tests (toxicity of solvent extracts and toxicity of plant powders) were performed with four different concentrations (25%, 50%, 75%, and 100%) of the extracts in three doses (4 ml, 8 ml, and 12 ml for toxicity of solvent extracts test and 4 g, 8 g, and 12 g for toxicity of plant powders test). Weevil mortality was assessed on the 1st, 3rd, 5th, 7th, and 14th days, while F1 progeny emergence was evaluated on the 14th and 28th days. Grain damage (weight loss and percentage germination) was measured at the end of the experiment. DCM solvent extracts of N. tabacum and J. curcas at 50%, 75%, and 100% LEC levels in all dose rates (4 ml, 8 ml, and 12 ml) were more toxic (100% mortality). ETA solvent extracts of N. tabacum and J. curcas caused 92% and 100% mortality at 100% LEC at a dose rate of 12 ml, respectively. Grain weight loss was highest in the control group and in plant powder treatments with ETA and DCM extracts (5.88%, 0.79%, and 0.64%, respectively). The results collectively suggest that the botanical extracts could be excellent insecticidal agents for S. zeamais. Thus, they could serve as potential sources to develop new anti-S. zeamais agents for maize weevil control.
Keywords: Adult emergence, insecticidal activity, maize weevil, Solvent extracts, Weevil mortality