Effectiveness of organophosphates and carbamates applied alone or in combinations with synthetic pyrethroids against field populations of whitefly, Bemisia tabaci, (Gennadius), on cotton in Egypt

Field tests were conducted determine the effectiveness of severs 1 organophosphorus and carbamate insecticides applied alone or in combinations .with synthetic pyrethroids, against the adult and immature stages of cotton whitefly, Bemisia  tabaci (Gennadius), on cotton. Acephate, alpha-cypermethrin, and thiodicarb applied alone at rates of 300, 25, and 400 g Al/ feddan were effective against adult populations throughout 18 days after application. Most selected insecticides alone, however, failed to have effective control of immature populations. Chlorpyrifos, thiodicarb, and acephate applied in combinations with cypermethrin at reduced rates, i.e. 456+24, 376+24, 276+24 g Al/ feddan, respectively, were significantly more effective for adult control than insecticides alone. Treatments of methamidophos + cypermethrin (276+24 g AI/ feddan and carbaryl + cypermethrin (1251+24 g Al/ feddan) gave a considerable control to immature populations compared with treatments of insecticides alone. Addition of alpha-cypermethrin to most selected insecticides, at reduced rates, did not significantly reduce adult infestation compared to insecticides alone. However, alpha cypermethrin added to carbaryl at reduced rates (10+1265 g Al/ feddan, respectively) provided excellent control to   populations than insecticides alone. All selected insecticides were significantly more effective in reducing adult populations when combined with alphamethrin, at reduced rates, than insecticides alone. Alphamethrin added to methamidophos or thiodicarb at rates of 10+290 or 10+390 g Al/ feddan, respectively; significantly decreased immature populations compared to insecticides alone.