Phylogenetic classification and physiological and ecological traits of Metarhizium spp.

The genus Metarhizium (Hypocreales: Clavicipitaceae) is mostly composed of entomopathogenic fungal species. Many of these species are anamorphic and difficult to distinguish morphologically. Furthermore, most isolates of this genus have a broad host range, making classification based on host-insect species uncertain. Molecular phylogenetic analysis based on DNA sequence information distinguishes these species well and revises the taxonomy of Metarhizium. However, in the revisions, the major groups within the genus, such as M. anisopliae complex, were classified regardless of their phenotypic differentiation. Therefore, the characteristics of the individual species remain unclear. To explore the species-specific characteristics of Metarhizium spp., the author performed a phylogenetic analysis and characterization of Metarhizium spp. in Japan. The results showed that strains of the M. brunneum and M. pemphigi clades exhibited cold-active growth characteristics and preferred forested environments over M. pingshaense. In the M. majus clade, a specialist of scarab beetles, isolates from different Scarabaeidae species, including the coconut rhinoceros beetle (Oryctes spp.) and flower chafer beetle (Protaetia orientalis), formed separate subclades and showed strong virulence against their original hosts. This review describes the current state of understanding of the taxonomy and species-specific characteristics of the genus Metarhizium, and includes the author’s own previous study.