## 3 Results  
### Evaluation of Metarhizium spp. Abundance  
The _Metarhizium_ spp. abundance in all treated field sites increased after application of the production strain. Although achieved CFU values in field site Styria 2 fluctuated during the seasons between 1480 and 53,850 CFU g\({}^{-1}\) dry weight soil (Figure 1A), this site, continuously planted with maize and treated annually with GranMet-P\({}^{\text{TM}}\) since 2012, has consistently shown significantly higher _Metarhizium_ CFU values than the untreated control site in all samples taken since spring 2015. A weak to moderate positive correlation between CFU and time (\(r\) = 0.4, \(p\) < 0.001) was determined for this field site (from first to last sampling). Styria 1 showed the highest variation in _Metarhizium_ CFU (Figure 1B; mean values of 720 up to 85,580 CFU g\({}^{-1}\) dry weight soil after first application). Although high CFU levels were not able to persist (no correlation between CFU and time; \(r\) = 0.06, \(p\) = 0.61), development of CFU was significantly different from control site (\(p\) < 0.001). In all Styrian field sites, including the control, _Metarhizium_ CFU increased significantly since first sampling in 2012 (\(p\) < 0.001)--where less than 100 CFU were found--up to at least 2800 CFU (evaluated in the soil of the control field in 2018).  
After the first application in Tyrol (March 2016), the abundance of _Metarhizium_ spp. increased from a maximum background value of 2500 CFU g\({}^{-1}\) dry weight soil to densities above the recommended abundance of 5000 CFU g\({}^{-1}\) dry weight soil (Figure 2). Significantly higher values were achieved after the second treatment and could be established throughout the last year of the field trial with a final fungal density of 11,386 CFU g\({}^{-1}\) dry weight soil. In comparison to the increase of the _Metarhizium_ spp. density in the treated field site (\(r\) = 0.41; \(p\) < 0.001), the CFU in the control fields in Tyrol showed a negative correlation of CFU and time (\(r\) = \(-\)0.48; \(p\) = 0.003). A decrease in CFU by a factor of five could be observed in samples from autumn 2018 (366 \(\pm\) 223 CFU) compared to the first sampling in 2016 (1912 \(\pm\) 536 CFU) on this experimental site.  
Figure 1: _Metarhizium_ spp. abundance in GranMet-P\({}^{\text{TM}}\) applied Styrian field sites. (**A**) shows soil samples taken from field site Styria 2, (**B**) Styria 1, both compared to untreated control site. Samples were taken in spring (Spr), summer (Sum), and autumn (Aut) from autumn 2012 to autumn 2018. The grey box indicates maximal background CFU levels before treatment, the dotted lines show recommended fungal density for sustainable control in the soil [1]. Lines and dots in box plots show median and mean CFU g\({}^{-1}\) soil dry weight, respectively; boxes show the 25 th and 75 th percentiles, whiskers the 10 th and 90 th percentiles.  
A significant positive correlation between percentage of isolates identified as BIPESCO 5 and amount of CFU was assessed for Styria 1 (\(r\) = 0.996; \(p\) < 0.001) and Tyrol (\(r\) = 0.742; \(p\) = 0.03). A moderate, but non-significant correlation occurred at the field site Styria 2 (\(r\) = 0.527; \(p\) = 0.18). The sustainable establishment of BIPESCO 5 varied between the field sites: Styria 1, which showed the highest variability of _Metarhizium_ spp. abundance, also showed poor persistence of BIPESCO 5 over time, while in all the other treated fields BIPESCO 5 was able to persist throughout the season.