Influence of formulation additives on the desiccation tolerance and storage stability of blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes)1

Abstract

Blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus were formulated with 10% lactose/1% bovine serum albumin (BSA) or various compositions of Fantesk™, a starch–oil composite prepared by jet-cooking an aqueous dispersion of starch and oil. Storage stability studies with wet blastospore formulations showed that maximum blastospore survival was achieved during low-temperature storage at −20°C with lactose/BSA formulations or starch–oil formulations supplemented with sucrose, zein protein, and whole milk. Under conditions of wet storage at −20°C, the addition of whole milk to starch–oil formulations significantly improved blastospore stability while the addition of sucrose or zein protein had no effect. In freeze-drying studies, no significant differences were seen in blastospore desiccation tolerance or in stability during storage at either 4 or −20°C when blastospores of P. fumosoroseus were formulated with lactose/BSA or starch–oil formulations with sucrose, zein protein, and whole milk. Freeze-dried blastospore formulations stored at 4°C showed no loss in blastospore viability after 3 months storage and blastospore formulations stored at −20°C showed no loss in viability during the entire 12-month study. For freeze-dried, starch–oil formulations, sucrose was shown to improve blastospore survival during the freeze-drying process. The addition of whole milk to starch–oil formulations significantly improved the stability of freeze-dried blastospores stored at 4°C. Compared to unformulated blastospore suspensions that showed blastospore settling after 30 min, suspensions of blastospores formulated with lactose/BSA or starch–oil composites remained stable for up to 2 h after mixing.