Liquid culture fermentation for rapid production of desiccation tolerant blastospores of Beauveria bassiana and Isaria fumosorosea strains

• We have developed a cost-effective liquid medium for blastospore production.
• Cottonseed flour is a suitable nitrogen source for rapid production of blastospores.
• B. bassiana and I. fumosorosea blastospores are desiccation tolerant and storage stable.
• Blastospores are more virulent toward whitefly nymphs than aerial conidia.

A major constraint to the commercial use of fungal biocontrol agents is the availability of low-cost production media and processes. Previous attempts in producing Beauveria blastospores using liquid culture fermentation processes required long fermentation times (6–8 days) and produced cells that had poor survival after desiccation and storage. In this study, isolates of Beauveria bassiana and Isaria fumosorosea were evaluated for blastospore yield, desiccation tolerance, storage stability, and biocontrol efficacy using fermentation media containing acid hydrolyzed casein or cottonseed flour as the nitrogen source. Cultures of B. bassiana and I. fumosorosea grown in media containing cottonseed flour produced high blastospore concentrations (>1 × 109 mL−1) after 3 days which is comparatively less expensive nitrogen source than acid hydrolyzed casein. The resultant air-dried blastospores (<3% moisture) of all fungal isolates survived drying (61–86% viability), irrespective of the nitrogen source tested. Storage stability at 4 °C varied with nitrogen source and fungal strain. Air-dried blastospores of B. bassiana strains showed half-lives >14 months in contrast to 9.2–13.1 months for I. fumosorosea. Blastospores of B. bassiana and I. fumosorosea killed Bemisia tabaci whitefly nymphs faster and required lower concentrations compared with aerial conidia. Our findings support the use of liquid culture fermentation as a cost-effective process to rapidly produce high yields of stable and infective blastospores of either B. bassiana or I. fumosorosea. These results support further evaluation of blastospore sprayable formulations for the control of soft-bodied insects.

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