Influence of Environmental Factors on Stability and Bioactivity of Certain Bioinsecticides Against Spodoptera littoralis (Boisd)

Background and Objective: The biological efficacy of bioinsecticdes gradually decreases with time especially if these compounds are subjected to environmental factors (e.g., temperature, UV, sunlight). Also the activity can be altered if not stored properly. The objectives of this work were to examine the influence of temperature, light, types of water and shelf storage on the stability of some formulations of two bioinsecticides and also to assess the bioactivity of these bioinsecticides against cotton leaf worm. Materials and Methods: The active ingredients of formulations of Tracer (spinosad 24% SC), Radiant (spinetoram 12% SC), Proclaim and Broact (emamectin benzoate 5% SG) were determined using HPLC post exposure of the compounds to several environmental factors, i.e. temperature, UV and sunlight and storage for 2 years under ambient condition. Parallel a bioassay test was carried out to assess the biological activity of each bioinsecticide against neonate and the 2nd larvae instar of the cotton leafworm Spodoptera littoralis. Data were subjected to statistical analysis using LD-P line version 1.0. Results: The results revealed that the loss (%) of all tested bioinsecticides after storage for 2 years was above the permissible limits of FAO specifications. In accordance with this trend, the bioassay tests showed a reduction in toxicity value (LC 50 s) for neonate and 2nd instar larvae of cotton leaf worm. Moreover, samples stored under direct sunlight and UV their biological activity were reduced to half values of their LC 50 . Photolysis of aqueous solutions for bioinsecticides reduced the half-life especially in the case of emamectin benzoate formulation. Conclusion: Results indicated that stability of bioinsecticides could be properly evaluated prior to submission for registration as these products showed less stability under storage at ambient conditions. Also the decision makers will take these results into considerations and examine such products case by case.