author(s)
Priyanka Borbaruah and Surajit Kalita

abstract
Laboratory experiments were conducted at Department of Entomology, Assam Agricultural University, Jorhat during 2016-18 to evaluate the bioefficacy of different solvent extracts of Chromolaena odorata (L.) King & Robinson (Family: Asteraceae) against Oligonychus coffeae Nietner (Acarina: Tetranychidae) and Helopeltis theivora Waterhouse (Hemiptera: Miridae) of tea by taking Neem seed kernel extract (NSKE) 0.15% EC, fenpyroximate 5 EC and deltamethrin 2.8 EC as check for comparison. The results revealed that the methanolic leaf extract of C. odorata was found to be superior recording 100.0% adult mortality of H. theivora at 48 hours after treatment (HAT) as compared to petroleum ether and water extract recording 86.67% and 33.33% adult mortality, respectively. Likewise, application of methanolic leaf extract of C. odorata was also found to be the most effectual recording the highest of 98.33% adult mortality of O. coffeae, as against 58.33% and 25.00% mortality in case of petroleum ether and water extract, respectively. The bioefficacy of methanolic leaf extract of C. odorata is comparable and at par with the toxicity of deltamethrin 2.8 EC @ 1ml/Land Fenpyroximate 5 EC@1ml/L recording 100.0% adult mortality of the both the insects at 48 HAT. The order of toxicity of different solvent extracts of C. odorata with respect to LC₅₀ values against H. theivora and O. coffeae was found to be methanol (0.056% and 0.603%) >petroleum ether (1.481% and 4.593%) >water (22.995% and 330.093%).