In vitro and in vivo culturing impacts on the virulence characteristics of serially passed entomopathogenic fungi.

Radial growth, sporulation, germination, spore-bound Pr1 and virulence of the strains of entomopathogenic fungi, Beauveria bassiana, Metarhizium anisopliae and Isaria fumosorosea, were evaluated on different nutritional conditions, with the objective to produce virulent spores, which may kill the host quickly. Variations in nutritional requirements existed among the fungal species as well as fungal strains. Except for M. anisopliae (EBCL 02049), all the selected fungi cultured on osmotic stress media attained lower colony growth (<32 mm), with low sporulation in M. anisopliae (strain 406) and B. bassiana (EBCL 03005). High sporulation was observed on potato dextrose agar of all the strains of entomopathogenic fungi, but high germination was observed only in the strains of M. anisopliae (93-98%). All studied strains except for I. fumosorosea (EBCL 03011) harvested from O. varians cadavers resulted in highly virulent spores with high spore-bound Pr1 activity. Exposure of larvae to suspensions of fungal spores (in vivo) of the strains of M. anisopliae and B. bassiana by immersion resulted in high level of fetal infection (≥ 98%). The results indicated that the influence of nutritional conditions on fungal growth and sporulation is strain dependent and serial subculturing of entomopathogenic fungi on PDA significantly affects the level of infection. Comparatively, in vivo spores harvested from Ocinara varians cadavers resulted in virulent spores with elevated levels of spore-bound Pr1.