Biocidal Effect of Some Algae Against the Cotton Leafworm Spodoptera littoralis Under Laboratory Conditions

Abstract

Traditional agricultural practices, such as the use of synthetic pesticides, lead to numerous problems including environmental contamination, generating pest resistance and harmful effects on non-target organisms. Consequently, these negative effects have emphasized the need to develop new efficient safe and eco-friendly natural alternatives to synthetic insecticides. Algal products play a significant role as chemical substitutes in agricultural applications. The current study to bioassay biocide effects of ten commercial algal products as an natural and safe bio-pesticides on 4th larval instar of cotton leafworm Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae). A high level of corrected mortality
was found for the algal product (Biocontra formulation) through exposure period of 96 hours under laboratory conditions. The toxicity against 4th larval instar of cotton leafworm insect increased as exposure time and concentrations increasing. Biocontra formulation caused comparatively the highest potential toxic activities >90% mortality and achieved the same value (92.5%) after 72 and 96 hours. exposure time. The highest mortality of Biocontra (80.0, 82.5 and 93.0%) were recorded with the highest concentration (10 mg\ml) after 48, 72 and 96 hours exposure times, respectively compared to control treatments. The least mortality percentages were observed with other concentrations 2, 4, 6
and 8 mg\ml after 48, 72 and 96 hours from exposure. Biocontra formulation was found to be the most toxic with LC50= 27.8 mg/ml to 4th larval instar of cotton leafworm after 96 hours from exposure. Results of treated larvae with LC50 of Biocontra formulation indicated that, the larval duration, female life span, fecundity and fertility are significantly affected by algae treatment. Moreover, protein content, Chitinase, β-esterase and GST significantly decreased compared to untreated larvae. Generally, algae are an important in agriculture system that they are been as biocontrol agent in the integrated crop managements, especially under modern climatic changes.