Species of the entomopathogenic fungal genus Metarhizium are found worldwide predominantly in the soil environment where they infect a broad spectrum of insects, but also associate with plant roots. To increase performance of Metarhizium as biological control agents against pests, fundamental ecological knowledge of Metarhizium is necessary. The present PhD project contributed to this knowledge, particularly of Metarhizium spp. occurrence and abundance within a single Danish agroecosystem, with emphasis on the molecular diversity and ecological traits. Metarhizium was isolated from bulk soil samples with “insect baits” and from the roots of several crop plants using selective media. The resulting isolates were separated into genotypes by applying microsatellite markers and DNA regions of these genotypes were sequenced. The study showed a highly complex Metarhizium community that comprised several sympatric species and genotypes. The isolated species and their genotypes were evaluated for ecological traits including UVB tolerance, temperature dependent in vitro growth, virulence and conidia production on infected cadavers, and mycelial growth from insect cadavers into the surrounding soil. The results showed a broad variety of ecological characteristics of the different genotypes, indicating their potential adaptations to different ecological niches within the agroecosystem. The presented knowledge of co-existence of diverse Metarhizium species and genotypes will be valuable for the development of biological control strategies.