Toxicity evaluation of emamectin benzoate against tobacco caterpillar (Spodoptera litura) by three different assay techniques

Toxicity of emamectin benzoate, an avermectin semi-synthetic insecticide, was evaluated in the laboratory to determine its performance on three different larval stages (5, 7 and 9 -day old) of tobacco caterpillar, Spodoptera litura during 2007–08. Three type of assay techniques viz. leaf-dip, potter's tower and thin-film were used, taking three different formulations of emamectin benzoate and were compared with conventional one, cypermethrin, against the test-insect Median lethal concentrations (LC₅₀) of the emamectin benzoate 1.9%EC against 5-day, 7-day and 9-day old larvae were recorded as 0.00005, 0.00017 and 0.0007%, respectively. Emulsifiable concentrates (EC, 1.9 and 5%) of emamectin benzoate outperformed the water-soluble granule (WSG, 5%) formulation, whereas, EC formulation of emamectin benzoate 1.9% EC was found better than 5% EC. Amongst test-methods, leaf-dip bioassay was suitable and sensitive for the test-insecticide, obviously for the fact that, emamectin benzoate is a stomach poison in addition to its contact mode of action.