Adulticidal activity of Nicotiana tabacum Linnaeus (Solanaceae) leaf extracts against the sweet potato weevil Cylas formicarius Fabricius 1798 (Coleoptera: Brentidae)
Lokesh KV, Kanmani S, Adline JD, Raveen R, Samuel T, Arivoli S and Jayakumar M
Sweet potato, Ipomoea batatas (Linnaeus) Lam. (Convolvulaceae), is a major staple food in several regions of the world. This crop is likely to make a growing contribution to the global food system as it plays a vital role in human diet. The sweet potato weevil, Cylasformicarius Fabricius (Coleoptera: Brentidae) is considered to be the single most destructive pest of Ipomoea batatas globally, particularly in the tropics and subtropics. The damage caused by this pest severely reduces the yield and greatly affects the tubers. Control measures for this pest involves application of chemical and synthetic insecticides, however the world is facing severe ecological challenges due to its use. Plants containing active insecticidal phytochemicals are gaining attention because of their broad spectrum insecticidal activity, safety, biodegradability and integrated crop management approaches as they are probable candidates for alternatives to chemical and synthetic insecticides. In the present study, the crude solvent (hexane, petroleum ether, dichloromethane, chloroform, ethyl acetate, acetone, methanol and aqueous) leaf extracts of Nicotiana tabacum were tested for their efficacy against the adults of Cylas formicarius at concentrations of 0.625, 1.25, 2.50, 5.00, 10.00 and 20.00µg/insect by the petridish bioassay method. Adult mortality was calculated 24, 48 and 72 hours after exposure. Overall assessment of the results indicated the chloroform and acetone extract of Nicotiana tabacum leaves to exhibit the highest activity against the adults of Cylas formicarius with one hundred per cent adult mortality after 72 hours of exposure and their LD50 and LD90 values were 0.49 and 0.81; 1.67 and 4.34µg/insect respectively. However, further studies are needed to make these phytopesticides more effective and to investigate their efficacy under field conditions since it is a well-known fact that the results of laboratory experiments cannot be transferred uncritically into conditions which hold for the environment.