Studies of the inheritance of virulence in the entomopathogenic fungus Metarhizium anisopliae

A forced heterocaryon was established between two auxotrophic conidial color mutants of Metarhizium anisopliae. From the heterocaryon, a prototrophic somatic diploid was selected which, in turn, yielded somatic segregants. The virulence of the original mutants, the somatic diploid, and the somatic segregants was evaluated on three species of mosquitoes as well as on Ostrinia nubilalis larvae. The virulence of the somatic diploid was comparable to that of the wild-type parental strain while the auxotrophic somatic segregants exhibited virulence approximately equal to that of the auxotrophic components of the heterocaryon. Putative somatic diploids were obtained between morphological mutants of the two species varieties (M. anisopliae var. minor and var. major). The presumptive diploids were avirulent for the insect species to which the parental strains exhibited virulence.