## 4 Discussion  
_Diabrotica virifera virifera_ has become one of the most important maize pests in Europe and many different studies have been carried out to obtain information on the biology and behavior of the pest, as well as control options against it [1; 23; 24; 25]. In this study, efficacy of the entomopathogenic fungus _M. brunneum_ BIPESCO 5 against _Diabrotica_ was compared under the following conditions: the product GranMet-PTM (registered for _Amphinallon solstitiale_ and _Phylopertha horticola_ control) was applied at the time of the general tillage in March/April with traditional agricultural equipment, reasonable workload for the farmers, heavily _Diabrotica_ infested fields with continuous maize cultivation or regular crop rotation. In addition, continuously cultivated maize fields not yet heavily infested were treated to ensure the establishment of the entomopathogenic fungus without the presence of the target pests as a preventive measure by increasing the pest antagonist. Figure 5: Non-metric multidimensional scaling (NMDS) using abundance of MLGs based on Bray-Curtis dissimilarities showing a different _Metarhizium_ population structure at the treated field sites Styria 1 (circles), Styria 2 (triangle), and Tyrol (square). Each symbol represents the population composition at a sampling time. Data shown is without the applied strain and from samples after the first application of the product. Hulls illustrate the different field sites Styria 1 (yellow), Styria 2 (light grey), and Tyrol (dark grey). We found significant differences in emerging adults in all heavily infested areas. The lowest number of adult beetles was observed in the field site with crop rotation (\(\geq\)5 adults m\({}^{-2}\)). This low number of adults per m\({}^{2}\) compared to an at least six times higher number found in continuous maize fields (treatment and control) is in accordance with results reported by [PERSON] et al. [26]. Although oviposition into non-maize fields near heavily infested maize fields occurs and therefore adult emergence in first-year maize can be observed, crop rotation still is the most effective method to quickly decrease _Diabrotica_ population in maize fields in Europe [26; 27; 28]. As already reported by [PERSON] et al. [1], _M. brunneum_ alone was not able to reduce the _Diabrotica_ population below an acceptable/zero-damage threshold level in our study due to the high pest population density (i.e., economic threshold value: \(>\)1 beetle per plant during any weekly counts in July and August, [29]). Nevertheless, plant health was better, and less lodging occurred in _Metrahizium_ treated field sites. The beneficial effect of _Metrahizium_ on different plants was also recognized in studies on rhizosphere colonization of the entomopathogenic fungus; results showed extensive root development, increased root length, improved plant growth, decreased stress in plants and improved availability of nutrients [30; 31; 32]. For maize crops in particular, it was shown, that, for instance, plant-growth-promoters were activated by the production of auxins at the roots by _Metrahizium_ spp. [31]. Furthermore, entomopathogenic fungi could colonize niches which otherwise are occupied by plant pathogens [31; 33]. Persistence of _M. brunneum_ at elevated abundance of approximately 5000 CFU g\({}^{-1}\) dry weight in soil is important for the successful control of soil-borne pests such as _Diabrotica_[1]. In Tyrol and Styria 2, BIPESCO 5 could be established (Table 2) and persisted in this density. The strain also persisted in the field site Styria 1, but not as sustainably as in the other field sites--here, annual reapplication was necessary to ensure the persistence of the strain throughout the planting season. Investigations on the diversity of _Metrahizium_ in soil has revealed a variable distribution of the different species worldwide, but with genetically closely related isolates across large distances [34]. [PERSON] et al.