Temperature adaptations of Cordyceps militaris, impact of host thermal biology and immunity on mycosis development

Temperature preferences, virulence properties and genetic relationships inferred from tef1-alpha gene sequencing were determined for Cordyceps militaris isolates from the Palearctic region. The variability of the mycelial growth rate of different isolates was extremely low at 5-30 °C. However, correlations among genetic variation, geographic origin and temperature responses were established. C. militaris cultures were not heat-active but were more psychrotolerant than Beauveria and Metarhizium isolates. The thermo-physiological state of the wax moth Galleria mellonella had a crucial role for the development of C. militaris. Larval diapause induced by decreasing temperature (15 °C) was most favourable for development of mycosis due to a drop in innate immunity. While fought off at 25 °C in the larvae, the infection could still be activated in pupae under cold conditions (15 °C). Differences in ecology and pathogenic strategies of C. militaris and the generalist fungi Beauveria and Metarhizium are discussed.