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 anisopliae, and Paecilomyces farinosus, were evaluated on a Sabouraud dextrose-based medium modified with the ionic solute KCl, the non-ionic solute glycerol, and an inert solute, polyethylene glycol (PEG) 600. The temperature ranges for growth of B. bassiana, M. anisopliae, and P. farinosus were 5-30, 5-40, and 5-30 degrees C, and optimum growth temperatures were 25, 30, and 20 degrees C, respectively. All three species grew over a similar a(w) range (0.90-0.998) at optimum temperatures for growth. However, there were significant interspecies variations in growth rates on media modified with each 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. anisopliae 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 relations for growth of these three species were constructed for the first time. The results are discussed in relation to the environmental limits that determine efficacy of entomogenous fungi as biocontrol agents in nature. Copyright 1999 Academic Press.