Comparative toxicity and biochemistry of organophosphates and pyrethroid compounds on both laboratory and field strain of the Cotton Leafworm Spodoptera littoralis (Boisd.)

Bioassay was carried out for monitoring resistance spectrum toward insecticides include organophosphates, Dursban H-48% EC (Chlorpyrifos) and pyrethroids Cyper (Cypermethrin 10% EC) in three different field populations (Gharbia , Kalubia and Menofeya Governorates) of the Cotton Leafworm, Spodoptera littoralis (Boisd.). Toxicity data based on LC50 values indicated that the pyrethroid Cyper (Cypermethrin 10% EC) is more toxic insecticide against the laboratory strain, while, the OP Dursban H- 48% EC (Chlorpyrifos) was less toxic. The development of resistance to organophosphates, Dursban H- 48% EC (Chlorpyrifos) and pyrethroids Cyper (Cypermethrin 10% EC) in field strains of the cotton leafworm, in relation to esterases, glutathione s- transferase, and phosphatases was studied. Field strains exhibited moderately high level of resistance to the tested insecticides. A significant increase in the activity of esterases, glutathione s- transferase suggests a good relation to resistance was detected. A high level of acid phosphatase and low level of alkaline phosphatase accompanied the level of resistance to pyrethroid and OP.