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 of the insecticidal activity against sensitive (laboratory) and resistance (field) strain is of great importance 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 revealed that the laboratory strain's larvicidal activity was higher than the field strain for both methomyl (LC50 = 413.0 ppm, LC50 = 581.49 ppm) and chlorpyrifos (LC50 = 219.73 ppm, LC50 = 275.94 ppm) insecticides. Moreover, the resistance of chlorpyrifos (RR = 1:1.26) was lower than that of methomyl (RR = 1:1.41) in laboratory and field strains, respectively.