Synergistic activity of sunlight protectants on some biocontrol agents as a new approach to control the cotton leaf worm, Spodoptera littoralis (Boisduval)

Bioinsecticides have gained attention as a sustainable and eco-friendly alternative to traditional chemical insecticides. They are target-specific, biodegradable, and reduce the development of insect resistance. However, their use is often limited by environmental instability, particularly under sunlight and UV radiation, which rapidly degrade active ingredients and reduce efficacy. Protective formulation, such as addition of UV-screening agents are needed to improve their durability and efficacy. This study investigates the efficiency of three UV protectants, Octylpalmitate, Tinuvin P, and UV- P in enhancing the persistence of some biocontrol agents, Dipel DF, Tracer, and Diacox under field conditions for 15 days to control the 4th instar larvae of Spodoptera littoralis. After 12 days, the residual effect of the all insecticides had markedly decreased, with Tracer showing the lowest persistence with zero mortality, and Diacox + UV protectant the highest. By 15 days, the sustained efficacy was absent, except for Diacox mixed with Octyl palmitate, Tinuvin P, and UV-P, which still caused 27, 32 and 12% mortality; respectively. The SDS-PAGE of S. littoralis larvae following 15 days of treatments revealed differences in the numbers of protein fragments between treated and control. New protein bands formed in the treated samples, while several normal bands disappeared.