Development, Characterisation, and Evaluation of a Bacillus thuringiensis-based Water-soluble Emulsion for the Management of Spodoptera frugiperda (J.E. Smith, 1797) under Laboratory Condition

Spodoptera frugiperda is one of the most destructive pests affecting economically important crops like maize and sorghum. Traditional management strategies rely highly on chemical insecticides, leading to environmental concerns and resistance development issues, necessitating alternative strategies for effective pest management. Biopesticides, particularly Bacillus thuringiensis (Bt)-based formulations, offer an environment friendly alternative due to their specificity and safety. However, the efficacy of the Bt often hindered by issues related to stability and application efficiency. This research focuses on development of formulation and evaluation of Bt-based water-soluble emulsion for the management of S. frugiperda. The Bt strain T414 containing cry and vip genes, was used to formulate a stable water-soluble emulsion. Mineral oil (light liquid paraffin) was chosen as a carrier oil, and Tween®80 and Span®80 were used as surfactant mixtures for enhanced miscibility, and stability. The final formulation, incorporating glycerol and trehalose as stabilizers, exhibited a droplet size of 177-187 nm and zeta potential of -28 mV, indicating good colloidal stability. The pH remained within an optimal range (6.92), and viscosity analysis confirmed shear-thinning behaviour, ensuring ease of application. Laboratory bioassay demonstrated that the emulsion formulation exhibited higher insecticidal activity, with a calculated LC50 of 0.006 µg/ml, compared to the spore-crystal mixture. This enhanced insecticidal efficacy suggests improved bioavailability of the active ingredients in the emulsion formulation. This study emphasizes the ability of Bt-based water-soluble emulsion formulation as environmentally safe and effective alternative for pest management, reducing dependence on chemical insecticides, subsequently promoting sustainable pest control.