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Toxicity and Some Biological Effects of Emamectin Benzoate, Novaluron and Diflubenzuron against Cotton Leafworm

Mervat H. A. Metayi, Moataza A. M. Ibrahiem and Dalia A. El-Deeb

Toxicity and sublethal effects of emamectin benzoate, novaluron and diflubenzuron were evaluated against the 2nd instar larvae of cotton leafworm (CLW). The joint toxic action of emamectin benzoate with novaluron or diflubenzuron was carried out. Emamectin benzoate (LC50 = 0.014 mg L-1) was 264.3 and 5707.1 times more toxic than novaluron (LC50 = 3.7 mg L-1) and diflubenzuron (LC50 = 79.9 mg L-1), respectively. Novaluron was approximately 21.6 times more toxic than diflubenzuron. After 24 hrs of exposure, all mixtures of emamectin benzoate (at LC10 or LC25) with novaluron or diflubenzuron (at LC10 or LC25) resulted in antagonistic effects with co-toxicity factors (CTFs) ranged between -25 to -700 except the mixture of emamectin benzoate at LC10 with novaluron at LC10 (CTF = 60). Mixtures of emamectin benzoate at LC10 with novaluron at LC10 and emamectin benzoate at LC25 with novaluron at LC25 resulted in potentiating effects after 48, 72 and 96 hrs of exposure. On the other hand, all mixtures of emamectin benzoate with diflubenzuron resulted in antagonistic effects. Emamectin benzoate, novaluron and diflubenzuron at the two sublethal concentrations reduced average larval weight, average time to the pupation, %pupation, pupal mean weight and %adult emergence compared to control. Results of this study verified the lethal and sublethal effects of emamectin benzoate, novaluron and diflubenzuron on the larval stage of S. littoralis, which negatively affect some biological parameters and insect population can be negatively affected. Emamectin benzoate, novaluron and diflubenzuron can be used for S. littoralis control and in resistance management programs, because their mode of action is different from pyrethroid, carbamate and organophosphate insecticides.