Comparative Toxicity of Some Insecticides to the Weevil, Crinorrhinus nebulosus Marshall (Coleoptera: Curculionidae)

Crinorrhinus nebulosus Marshall causes extensive damage to the leaves of Terminalia arjuna Bedd. and Terminalia tomentosa W. & A. for chemical control of this pest eight insecticides, an organochlorine namely Endosulfan, five organophosphates, viz., Malathion, Dimethoate, Quinalphos, Dichlorvos and Methyl-o-demeton and two pyrethroids namely, Cypermethrin and Fenvelerate were screened in the laboratory to find out their potency against adults of C. nebulosus. Cypermethrin proved to be most toxic and least toxic was Methyl-o-demeton. Against Methyl-o-demeton, Cypermethrin was 37.799, velerate-19.263, Malathion-3.376, Dimethorate-1.789, Endosulfan-1.427, Quinalphos-1.304, Dichlorovos-1.244 times toxic to the adults of C. nebulosus. Order of toxicity was almost the same at LD 50 and LC 90.