Biochemical and Biological Influences of Sub-Lethal Concentrations of Emamectin Benzoate and Certain IGR Insecticides against Spodoptera littoralis (Lepidoptera: Noctuidae)

Abstract

Toxicity and sub-lethal effects of Emamectin benzoate and IGR 's (lufenuron -flufenoxuron) were evaluated against the 2 nd instar larvae of cotton leafworm, Spodopter alittoralis. The biochemical influences of these agrochemicals with the polyphenol oxidase (PPO) of the treated larvae were investigated (invivo). Emamectin benzoate (LC 50 = 0.007 mg L -1 ) was approximately 34 and 83 times more toxic than lufenuron (LC 50 = 0.24 mg L -1 ) and flufenoxuron (LC 50 = 0.58 mg L -1 ), respectively. Lufenuron was approximately 2 times more toxic than flufenoxuron. The 2 nd instar larvae treated with the sublethal concentrations (LC10 and LC 25) of emamectin benzoate, lufenuron or flufenoxuron showed significant (P < 0.05) reduce of larval body weights, pupation%, pupal mean weight and adult emergence%. While the average time of the pupation for the larvae that given concentrations equivalent to the LC 10 and LC 25 of lufenuron and flufenoxuron, were significantly longer than the untreated larvae. On the other hand larval duration for the larvae that given concentrations equivalent to the LC 10 and LC 25 of emamectin benzoate did not differ significantly compared with the untreated larvae. The fecundity and fertility were strongly reduced in all insecticide treatments compared with check untreated. The PPO activity was partially decreased in the treated larvae (with all insecticide treatments) in a concentration dependent manner. These results suggest that, sublethal concentrations of emamectin benzoate, lufenuron and flufenoxuron may reduce the population growth of S. littoralis by affecting its development and reproduction.