ARS | Publication request: EFFECT OF THE RELATIVE HUMIDITY OF DRYING AIR ON SURVIVAL OF LIQUID CULTUREPRODUCED BLASTOSPORES OF PAECILOMYCES FUMOSOROSEUS

Submitted to: Society of Invertebrate Pathology
Publication Type: Abstract Only
Publication Acceptance Date: July 21, 1995
Publication Date: N/A

Technical Abstract: The fungus Paecilomyces fumosoroseus is being developed as a bioinsecticide for controlling sweetpotato whitefly (Bemisia tabaci) and other soft-bodied insects. We have developed a liquid culture method for rapidly producing high concentrations of desiccation-tolerant P. fumosoroseus blastospores. In this study, we evaluated the impact of drying air relative humidity on spore survival after drying. Shake flask cultures of P. fumosoroseus grow for four days at 28 deg C and 300 rpm in a rotary shaker incubator yielded 1-3 X 10**9 blastospores/mL. Blastospores were separated from hyphal biomass with cheesecloth, mixed with diatomaceous earth (2 X 10**10 spores/g), and vacuum filtered to remove excess liquid. The blastospore preparations were air dried at 22 deg C in a humidity-controlled plant growth chamber and in a biological containment hood. Drying air with relative humidities between 24 and 75% were tested. Under the conditions of this test, 66-96% of the blastospores dried in air with a relative humidity of 50% or higher survived overnight drying. These spore preparations contained 2-5% moisture. Survival of blastospore preparations air dried at relative humidities below 50% was more variable (6-76%) and the moisture content of the blastospore preparations was consistently lower (2.5-1.5%). Preliminary data suggest that P. fumosoroseus blastospores air dried at relative humidities above 50% survived storage at 4 deg C better than those dried at lower relative humidities. Work is underway to determine if slower drying times and/or higher final moisture content enhance blastospore survival and stability after air drying with high humidity air.