Optimization of a wettable powder formulation for two native Bacillus thuringiensis strains

The objective of the present study was to optimize awettable powder formulation for twoiranianBtstrains (YD5 and KH4) in order to enhance efficiency and durability as biological agent against lepidopteran and coleopteran pests.Mass production of the mentioned strains was done in a batch fermentor based on the peviouselyoptimized economical medium and fermentation conditions, and the final concentration was achieved 6 ×109(CFU/mg). To optimize formulation for the strains, 25% spore crystal mixture of the strain and 75% adjuvants including different fillers, surfactants, materials enhancing durability, anti UV materials, suspensors, wetters, palatability materialsand antimicrobial materials in the framework of 5 statistical treatments were used.Based on the results, the treatment containing milk powder (4%), perlite (6%), irosile (2%), sodium loril sulfate (8%), Alkaline naphthalene (20%), starch (10%), gelatin (9%), sugar (10%), potassium surbate (1%), Casein and gluten (2%), potassium dioxide (3%) and monosodium glutamate (0/2 %) showed maximum suspensibility (73 and 71 %) and wetability (25 and 24%) for YD5 and KH4 strains, respectively, and selected for the next experiments. The selected formulation for both strains had a white to grey color, 6-7 % moisture content, and pH6.1 and 6.2. Crystals in both formulations were stable whithout any changes during one year. The LC50 of the selected formulation for YD5 and KH4 strains againstlarvae cotton bollworm and elm leaf beetle was 550 and 510 ng/cm2 leaf, respectively.