Spatial distribution of Metarhizium clade 1 in agricultural landscapes with arable land and different semi-natural habitats

Metarhizium spp. are insect pathogenic fungal species, which are widely used as biological control agents for pest insects. The natural occurrence of Metarhizium spp. and their potential for natural regulation of pest insects have obtained more and more attention because of an increasing demand for sustainable agriculture. Therefore, the interest on management strategies enhancing the natural occurrence of Metarhizium spp. and consequently the success of conservation biological control has been growing. Such strategies include habitat management as well as establishment of semi-natural habitat types, which may provide a refuge for Metarhizium spp. and may allow for recolonization of adjacent arable fields. The present study provides an overview of the densities of Metarhizium clade 1 consisting of M. majus, M. guizhouense, M. pinghaense, M. anisopliae, M. robertsii, and M. brunneum in different habitat types at field, local, and regional scales in Swiss agricultural landscapes. Soil samples were analyzed for Metarhizium clade 1 densities with a cultivation-independent qPCR-based detection and quantification tool. Based on this tool, 19.3% of 176 collected soil samples were tested positive for Metarhizium clade 1. The densities of Metarhizium clade 1 were heterogeneously distributed among the soil samples and differed significantly among sampled areas as well as sites. Despite this heterogeneity significant habitat-specific associations were observed. High Metarhizium clade 1 densities were found in soil samples collected from low-input permanent grassland and improved field margins indicating that both semi-natural habitat types may provide potential refuges for Metarhizium clade 1 species. Based on these results, more detailed analyses can be performed in permanent grassland and improved field margins to identify factors, which may promote the natural occurrence of Metarhizium clade 1 species and improve their function as natural regulator of pest insect populations.