TOXICITY OF SOME CONVENTIONAL AND NONCONVENTIONAL INSECTICIDES AGAINST COTTON LEFWORM, Spodoptera littoralis (BOISD.)

Abstract

The ovicidal action of three novel compounds (emamectin benzoate, methoxyfenozide, pyridalyl) and conventional insecticide (methomyl) against (0-24, 24-48 and 48-72 hours age) eggs of Spodoptera littoralis was assessed. The toxic activity of emamectin benzoate, methoxyfenozide, pyridalyl and methomyl against 4th instar larvae of laboratory and field strains of S. littoralis were carried out. Also, the build up of resistance of each tested compound in the field strain was calculated. The joint toxic action of emamectin benzoate, methoxyfenozide and pyridalyl with tested insecticides was also studied. The obtained data revealed that emamectin benzoate gave an ovicidal activity higher than methomyl, methoxyfenozide and pyridalyl. Also, emamectin benzoate was a superior potent compound against 4th instar larvae of S. littoralis followed by methoxyfenozide, with LC50 values were 0.007 and 0.932 ppm after 72 hrs, while methomyl was the least toxic one, LC50 value was 95.60 ppm. The build up of resistance of tested compounds indicated that the resistance ratio of methoxyfenozide and methomyl were 5.9 and 5.8 fold as the laboratory strain, while the resistance ratio of emamectin benzoate and pyridalyl were 2.7 and 1.9 fold as the laboratory strain. In respect with the joint toxic action, the all mixtures of the tested insecticides showed highly antagonisms effect as calculated by the co-toxicity factors. The present study suggests that emamectin benzoate is very effective in the control of S. littoralis.