## 3 Results
### Pest Abundance and Plant Injury  
In the heavily infested areas in Styria the _D. v. virgifera_ population density continued to increase over the years. On average, the number of caught beetles doubled every year, up to 130 beetles per m\({}^{2}\) caught with the emergence trap system in 2018 on the untreated maize field. Only the crop rotation in combination with the biocontrol agent in Styria 1 ensured a significant reduction of the pest, with only five emerging beetles per m\({}^{2}\). The number of adult _Diabrotica_ evaluated in Styria was significantly different between all field sites (\(p\) < 0.001, data not shown). Although _Diabrotica_ population pressure in Styrian maize fields was very high (Table 1), both treated field sites showed no or only low damage of maize plants. As for the untreated control area, the extent of the damage was affected by the prevailing weather conditions. In the field season 2016 more than 30% of the maize plants showed plant lodging. In 2017, no lodging was observed, but due to the lack of water, plants dried up, were low growing, and fewer-to-no corn cobs had developed. In 2018, less than 1.25% of plants showed lodging due to the sufficient precipitation during this season (Figure 3). Overall, no root injuries were observed in 2018.  
Figure 2: _Metarhizium_ spp. abundance in Tyrolean field sites. Samples were taken in spring (Spr), summer (Sum), and autumn (Aut) from 2016 to 2018. Grey box indicates maximal background CFU levels before treatment, dotted line shows recommended fungal density. 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.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Bad Radkersburg (Styria)**} & \multicolumn{4}{c}{**Oberndorf/ St. Johann I. T. (Tyrol)**} \\ \hline  & & & & & & & & & & & & \\
2016 & x & \textless{}250 & \textgreater{}250 & - & 27/41 & - & 260 & 0 & 226 & - & 27/38 & 36 \\
2017 & 4429 & 0 & 980 & - & 27/38 & 36 & 749 & 0 & 549 & 2.88 & 27/37 & 31 \\
2018 & 7336 & 0 & 1488 & 1.66 & 27/38 & 36 & 1008 & 0 & 475 & 1.35 & 27/38 & 32 \\
2019 & 4588 & 10 & 1041 & 0.63 & 27/38 & 36 & 753 & 0 & 250 & 0.75 & 28/40 & 37 \\
2020 & 7023 & 72 & 1193 & 1.53 & 27/38 & 37 & y & - & - & - & - \\ \hline \multicolumn{10}{c}{cw calendar week; x the exact number of beetles was not evaluated, only classified as \textless{}250 or \textgreater{}250 beetles per trap; y not evaluated;—not} \\ \multicolumn{10}{c}{calculated due to missing data.} \\ \hline \end{tabular}
\end{table}
Table 1: Number of beetles in the trial region evaluated with PAL sticky traps (CSALOMONTM, Hungary) in the regions Bad Radkersburg and Oberndorf/St. Johann in Tyrol from 2016 to 2020. Shown is the mean number of beetles over the season per trap with minimum (min) and maximum (max) number of beetles per week.  
Figure 3: Percentage of plants for each damage level assessed in the years 2016 to 2018 in Styria. Healthy plants are indicated as upright, completely fallen plants as lodging. The damage for Styria 1 in 2017 could not be surveyed due to the cultivation of pumpkin (_Cucurbita pepo_ L. _var. styriaa_) as part of the crop rotation.  
In Tyrol, a total of only two beetles were caught in the emerging trap, confirming that the pest has reached Tyrol, however, in such small numbers that damage to the crop was not to be expected: plant health was not yet affected by larval root feeding, all plants were scored class 1 according to [PERSON] et al. (2018). Nevertheless, data obtained from the pheromone traps revealed a two-to-three-fold increase in _Diabrotica_ density per year (Table 1).