Delayed Germination of Beauveria bassiana Conidia after Prolonged Storage at Low, Above-freezing Temperatures

Powder formulations were prepared with conidia of the entomopathogenic fungus Beauveria bassiana strain 447 originally isolated in Brazil from the red imported fire ant, Solenopsis invicta. The carrier materials used in formulations included talc hydrous magnesium silicate , silica gel, powdered rice and cornstarch. The formulations were stored in plastic containers under three conditions: a ambient temperature 15-38 C ; b refrigerator 6 2 C ; and c freezer 10- 7 C . Formulations stored under ambient temperature conditions completely lost viability after 1-8 months. Unformulated conidia stored under ambient conditions were totally unviable after just 2 months. All formulations stored under refrigerator and freezer conditions maintained 100 viability for 7 years. The virulences of the conidial preparations against adult workers of the fire ant, S. saevissima, and the sugarcane borer, Diatraea saccharalis, were higher for fresh conidia or conidia stored in the freezer than for conidia stored in the refrigerator. After 30 months of storage, the unformulated conidia and the formulations stored in the refrigerator showed slow germination and had low virulence. There was a strong correlation between the rate of germination and the virulence toward D. saccharalis, but not toward S. saevissima.