Larvicidal activity assessment for anticholinesterase insecticides against laboratory and field strains of Egyptian cotton leafworm, Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae)

Anticholinesterase insecticides are widely applied in crop protection programs for the chemical control of Egyptian cotton leafworm ( Spodoptera littoralis ).Therefore, the continuous evaluation for the insecticidal activity against sensitive (laboratory) and resistance (field) strains is very important to reconsider their applicability. Herein, the larvicidal activity of carbamate esters (methomyl) and organophosphorus (chlorpyrifos) was evaluated via feeding bioassay technique under laboratory conditions against second instar larvae of the Egyptian cotton leafworm ( spodoptera littoralis) . The results reviled that the larvicidal activity for the laboratory strain was higher than the field strain for both methomyl (LC 50  = 413.0 ppm, LC 50  = 581.49 ppm) and chlorpyrifos (LC 50  = 219.73 ppm, LC 50  = 275.94 ppm) insecticides. Moreover, the resistance of chlorpyrifos (RR = 1:1.26) was lower than that for methomyl (RR = 1:1.41) in laboratory and field strains, respectively.