**5. Conclusions**

According to the results, the effect of fungal entomopathogen *M. anisopliae* strain NCAIM 362 in WP formulation against *M. melolontha* larvae in sweet potato is not an effective biological control method. Even if the soil parameters are identical, the effect of α-cypermethrin against *Melolontha* larvae is more significant, and less survived larvae and damaged tubers can be detected after the insecticidal treatment. Under open field conditions, some soil managemen<sup>t</sup> methods such as compost supply and textile cover may enhance the effect of *M. anisopliae*, but further research is needed to test other species of the *Metarhizium* genus to find if they are an effective agen<sup>t</sup> in sweet potato sustainable pest control.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2309-608X/6/3/116/s1, Figure S1. The scheme of the field experiment, Figure S2. Plots of the field experiment with or without foil cover, Figure S3. Experimental greenhouse at the beginning of the season, Figure S4. Experimental greenhouse in the middle of the season, Figure S5. Genus-level of the bacterial composition of sweet potato soil, Figure S6. NMDS ordination of soil samples based on the Bray-Curtis distance of the bacterial OTUs, Figure S7. Rarefaction curves of OTUs based on 16S rRNA gene amplicon sequencing data, Table S1. Bacterial species numbers (sobs, ACE and Chao-1) and diversity indices (inverse Simpson and Shannon-Weaver) calculated from 16S rRNA gene amplicon sequencing data. KI—represents control P+, KII—represents control P-, MI – represents Metarhizium P+, MII—represents Metarhizium P-, VI- represents insecticide P+, VII- represents insecticide P- treatment.

**Author Contributions:** B.P.-C., J.B., A.B., and F.T. performed the field experiments; B.P.-C., J.B., and A.B. performed the greenhouse experiments; B.P.-C. and J.B. collected the data; S.T. performed the soil analyses; A.S. and Z.M. performed the soil microbial community analyses; É.A. performed the biological activity assay; A.B. and J.B. performed the data analyses; A.B. and J.B. prepared figures and tables; A.B., J.B., and F.T.B. wrote the main manuscript text; A.B., F.T., and F.T.B. edited and corrected the language of the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Institute of Research Programs of the Sapientia Hungarian University of Transylvania gran<sup>t</sup> no. 21/2/12.06.2019. The work was also supported by the Ministry for Innovation and Technology within the framework of the Higher Education Institutional Excellence Program (NKFIH-1159-6/2019) in the scope of plant breeding and plant protection research at the Szent István University.

**Acknowledgments:** This article was founded by The authors would like to express their special thanks to Gyula Bohár (Biovéd 2005 Kft.) for providing formulated strains of *M. anisopliae*, to Artúr Botond Csorba, Éva Simon, Zoltán Dezs˝o Vajda and Csaba Fazakas for helping in field experiments, and to Tamás Felföldi, Eszter <sup>R</sup>ápó, István Máthé and László Veress for their help in lab works.

**Conflicts of Interest:** All authors declare that they have no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
