Toxicity of tobacco Nicotiana tabacum Linnaeus (Solanaceae) leaf extracts to the rice weevil Sitophilus oryzae Linnaeus 1763 (Coleoptera: Curculionidae)

Abstract

BackgroundRice is the agricultural commodity with the third highest worldwide production and losses in rice storage due to insect pests may drastically affect the food availability for a large number of people. One of its serious pests in tropics is the “rice weevil”, Sitophilus oryzae. Although few effective fumigants are available, there is a global concern about environmental pollution, toxicity to non-target organisms, and pesticide residues. Botanicals are a promising source of pest control compounds as the pool of plants possessing insecticidal substances are enormous and have generated extraordinary interest in recent years as potential sources of natural insect control agents. The present study was conducted to determine the toxicity of tobacco (Nicotiana tabacum) leaf extracts as an alternative to synthetic insecticides in the management of rice weevils. The crude solvent leaf extracts of N. tabacum were analyzed for its phytochemical compounds via GC-MS and tested for its toxicity to the adults of S. oryzae at concentrations of 0.625, 1.25, 2.50, 5.00, 10.00, and 20.00 mg/L by Petri dish bioassay method. Adult mortality was calculated 24, 48, and 72 h after exposure.ResultsThe constituent compounds in the chloroform and acetone revealed 13 compounds represented by benzene carboxylic acid ester, alkaloids, and steroids. The major compounds found in GC-MS analysis are nicotine, nicotinonitrile, nornicotine, nicotinic acid, neonicotine, cotinine, indole, farnesol, sclareol, 9,12-octadecadienoic acid, squalene, palmitic acid, and 15-tetracosenoic acid methyl ester. Overall assessment indicates that the chloroform and acetone extracts of N. tabacum leaves exhibited the highest adulticidal activity against S. oryzae. Their LD50 values were 1.62, 0.64, and 0.48; 1.54, 0.83, and 0.48 mg/L after 24, 48, and 72 h of exposure respectively. In addition, the petroleum ether extract also indicated high adult mortality with LD50 value of 0.53 mg/L only at 72 h.ConclusionsThe present research has documented its first report for the management of rice weevil using tobacco leaf extracts, and therefore on the basis of the results of the present study, it is highly encouraging to note that the use of tobacco leaf extracts with its excellent insecticidal activity owing to the action of nicotine would be economically feasible to alleviate the rice weevil problem.