Water and temperature relations of growth of the entomogenous fungi Beauveria bassiana, Metarhizium anisopliae, and Paecilomyces farinosus

The effects of temperature (5-50 degrees C), water availability (0.998-0.88 water activity, a(w)), and a(w) x temperature interactions (15-45 degrees C) on growth of three entomogenous fungi, Beauveria bassiana, Metarhizium a nisopliae, and Paecilomyces farinosus, were evaluated on a Sabouraud dextro se-based medium modified with the ionic solute KCl, the non-ionic solute gl ycerol, and an inert solute, polyethylene glycol (PEG) 600. The temperature ranges for growth of B. bassiana, M. anisopliae, and P. farinosus were 5-3 0, 5-40, and 5-30 degrees C, and optimum growth temperatures were 25, 30, a nd 20 degrees C, respectively. All three species grew over a similar a(w) r ange (0.90-0.998) at optimum temperatures for growth. However, there were s ignificant interspecies variations in growth rates on media modified with e ach of the three a(w)-modifying solutes. Growth a(w) optima ranged between 0.99 and 0.97 on KCl-, glycerol-, and PEG 600-modified media for M. anisopl iae and P. farinosus. B. bassiana grew optimally at 0.998 a(w), regardless of a(w). Comprehensive two-dimensional profiles of a(w) x temperature relat ions for growth of these three species were constructed for the first time. The results are discussed in relation to the environmental limits that det ermine efficacy of entomogenous fungi as biocontrol agents in nature. (C) 1 999 Academic Press.