Production of wettable powder biopesticide formulation from two superior Bacillus thuringiensis strains native to Northern Iran
Biological pest control agents have many advantages such as low risk, low cost and specific effect. They can be an effective alternative to conventional chemical insecticides. Bacillus thuringiensis (Bt) is the most widely used biopesticide due to its efficacy to control pests. From an economic perspective, and to improve efficacy and persistance, development of suitable new formulations is always significant in the production and application of microbial biopesticides.
The aim of this study, was to produce a wettable powder (WP) formulation of two superior Bt strains (Bt-72) and (Bt-73) native of Northern Iran. In previous research, these strains were isolated, their genetic characteristics were identified and preliminary bioassays conducted. The two Bt strains were produced in a liquid medium culture with low-cost resources in the fermenter. The mixture of spore-crystals was recovered and dried. Pure powder of spore-crystals was obtained with final concentration around 2 × 1010 (CFU/mg). The formulation was prepared from mixing the 50 % spore-crystal mixture from each of the two strains together with 50 % adjuvants including different fillers, surfactants, materials enhancing durability, protective materials against ultraviolet light, suspensors, wetters, palatability materials, antimicrobial materials and insect larvae attractive agent.
Biological, physical and chemical tests of the prepared formulations based on the protocol CIPAC (1970) were done. Phytotoxicity was examined to evaluate which effective formulation could be selected. The results of these tests showed that the superior formulation, had 73 % suspensibility (25 S) for wetting time, 2 × 1010 spore-crystals CFU/mg), 920 mg/ml deltaendotoxin and high durability - about two years. The results of laboratory bioassays showed that this formulation had the highest mortality rate - about 95 %, and its LC50 value on second larvae of tobacco bulworm (Helicoverpa armigera) was 490 ng/cm2 leaf. Economically, this formulation is recommended for commercialisation.