Species-Discriminating Diagnostic PCR, Ribosomal Intergenic Spacer-Based Single-Marker Taxonomy and Cryptic Descriptions of the Fungal Entomopathogens <i>Metarhizium hybridum</i> and <i>Metarhizium parapingshaense</i>

(1) Background: Potentially arthropod-pathogenic and plant-associated <i>Metarhizium</i> fungi are of high interest for basic research, biological pest control and plant growth promotion. Unambiguous species delineation enabling the taxonomic assignment of new isolates and the identification of new <i>Metarhizium</i> species is of crucial importance for both research and application. Recently, the new species <i>Metarhizium hybridum</i> and <i>Metarhizium parapingshaense</i> were introduced on the basis of phylogenomic studies. (2) Methods: Neighbor- joining and Bayesian inference-based phylogenetic reconstruction of ribosomal intergenic spacer (rIGS) sequences were used to critically evaluate new species introductions. A species-discriminating diagnostic PCR tool for <i>Metarhizium</i> was adapted to <i>M. hybridum</i> and <i>M. parapingshaense</i>. GenBank database mining was performed to identify cryptic descriptions of the new species. (3) Results: The introduction of <i>M. hybridum</i> and <i>M. parapingshaense</i> was corroborated by rIGS sequence comparison. Data mining revealed cryptic first descriptions of <i>M. hybridum</i> from Canada, China, Colombia, Costa Rica, Cuba, Honduras, Mexico, New Zealand, the USA and the Philippines, and of <i>M. parapingshaense</i> from China, India, Japan, the Philippines and South Korea. (4) Conclusions: Results support the reliability of rIGS as a single taxonomic marker for species-level identification of <i>Metarhizium</i> fungi. Species-discriminating diagnostic PCR was successfully adapted to enable the sequencing-independent identification of the confirmed new species <i>M. hybridum</i> and <i>M. parapingshaense</i>.