Production of stable, infective yeast-like blastospores of the bioinsecticidal fungus Beauveria bassiana using liquid culture fermentation

While the entomopathogen Beauveria bassiana is one of the most widely used fungal biocontrol agents for insect control, its use in developed countries such as the U.S. has been limited due to the cost of conidia production using solid substrate fermentation. Conidia production by B. bassiana cultures on moistened grains is labor intensive, difficult to scale-up, and prone to significant losses due to contamination. We have developed a low-cost liquid culture fermentation method for yeast-like blastospores of B. bassiana. After 2 days growth in shake flasks or stirred tank bioreactors, cultures of B. bassiana yielded >1 x 10¹² blastospore L^-1. Over 70% of the liquid culture produced blastospores survived air- or spray-drying to less than 4% moisture and remained viable for more than one year when stored at room temperature using appropriate packaging methods.  Bioassays showed that dried blastospores were significantly more effective in infecting and killing the silverleaf whitefly when compared to solid substrate produced conidia. These results suggest that liquid culture fermentation has potential to be a cost effective method for commercially producing stable, effective propagules of the insect-killing fungus B. bassiana.