Comparative toxicity and biochemical impacts of several conventional insecticides on cotton leafworm [electronic resource].

Includes references.

The objective of this research was to evaluate the susceptibility of both the laboratory and the field strain of 2nd and 4th instars larvae of the cotton leaf worm Spodoptera littoralis (Boisd.) to two organophosphorus (Profenofos and Chlorpyrifos), two carbamates (Carbaryl and Thiodicarb) and two synthetic pyrethroid insecticides (Fenpropathrin and Beta-cyfluthrin). Based on resistance ratio the fold of resistance varied considerably according to the chemical structure of the studied insecticides and the instar of larvae. Data revealed that small differences in LC₅₀ values were observed between the laboratory and the field strains as demonstrated by resistance ratio of 0.892, 0.939and 1.757 fold for Profenofos ,Fenpropathrin and Chlorpyrifos relating to 2nd instar larvae, respectively. Thiodicarb showed the highest resistance ratio, followed by Beta-cyfluthrin and Carbaryl reached 3.843, 3.516 and 3.414 fold on the same instar larvae , respectively .The LC₅₀ values of both the laboratory and the field strains on 4th instar larvae were remarkably higher compared with 2nd instar larvae. Carbaryl gave the highest resistance ratio, followed by Chlorpyrifos, Profenofos being 6.593, 3.721 and 3.633 fold, respectively. There were low level of resistance ratio to Thiodicarb, Beta-cyfluthrin and Fenpropathrin with degree of fold 1.061, 0.528 and 0.327 , respectively . In addition the effect of tested insecticides on the activity of esterases (aliphatic esterase and α- & β-esterase), phosphatases (acid and alkaline phosphatase), transaminase (AST and ALT) and carbohydrate hydrolyzing enzymes (amylase and invertase) were evaluated on the field strain of Spodoptera littoralis (Boisd.) compared with the laboratory strain.

Summary in Arabic.

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