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Abstract
The resistance level of three field strains of Pectinophora gossypiella (Saunders) collected from three different Governorates representing the Nil Delta, i.e. El-Sharkia, El-Menofia and El-Gharbia was monitored during the three cotton season, 2004-2006 to different insecticides, i.e. two organophosphorus (OP) and six pyrethroids. Based on the calculated LC50 values, resistance ratio and toxicity index of the tested compounds, the three tested strains exhibited higher resistance level against the OP chlorpyrifos than profenofos which showed the higher toxicity during the selected cotton seasons. Within the pyrethroids, high resistance ratio was observed against fenvalerate, esfenvalerate and deltamethrin, while fenpropathrin was the most toxic compound followed by gamma – cyhalothrin and lambda – cyhalothrin during 2004 – 2006 seasons (gamma – cyhalothrin was only tested in seasons 2005 and 2006).