**4. Conclusions**

In the current study, we compared several aspects of the interaction of two *B. bassiana* strains (GHA and Bb-C001) with the Chagas disease vector *T. infestans*. Both fungal strains did not show any differences on physiological parameters evaluated; i.e., conidial yield, viability, and radial growth, the same as virulence against nymphs and adults. However, the expression of genes encoding nonribosomal peptides was quite different, being the bassianolide syntethase gene the most expressed in Bb-C001, and beauvericin and tenellin synthesase genes the most expressed ones in GHA [13], in all cases peaking at day six post infection. The immune response by measuring the expression of antimicrobial peptides was late and peaked at day nine post inoculation, when the infection process seems to be irreversible. However, differences in the expression of these immune-related genes were observed between pyrethroid-susceptible and pyrethoid-resistant insects. In summary, the infection with both strains develops with similar virulence but the expression of antimicrobial peptides inside insects is different between strains. This finding is an important conclusion from this work, because it confirms that once the fungus reaches the hemocoel, the insect has very little chance to survive the fungal infection despite the activation of the immune response as a last-ditch effort to overcome the fungus. Thus, the main battle in this fungus-insect interaction is to try enter the host by any of the different routes available [36], which determines either a successful infection and the death of the host or an effective defense by the host. Overall, we conclude that the strain coming from of the Gran Chaco region (Bb-C001) is a promissory candidate for the development of a fungal formulation to control both pyrethroid-susceptible and pyrethroid-resistant *T. infestans*. Further studies are underway to evaluate massive production and formulation methods for this strain.

**Author Contributions:** Investigation, analysis and interpretation of data, critical review of the draft, L.V.B.; conceptualization, analysis and interpretation of data, writing the manuscript, N.P. and R.M.C.; analysis and interpretation of phylogenetic data, M.S. and N.P.; analysis and interpretation of dual qPCR data, M.C.M. and N.P.; funding acquisition, critical review of the draft, L.B.N., A.G. and R.M.C.; supervision, N.P. and R.M.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Research Council of the National University of Salta (PA CI N◦ 2474 and 2353/0), and also supported by Ministerio de Salud Pública de Salta, and Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). NP is a member of the CONICET Researcher's Career, Argentina.

**Acknowledgments:** The authors thank Andrea Guanuco, Paula Arnal, Carlos Enriquez and José Solis for expert assistance in the laboratory, and Rosana Del Cid for language revision.

**Conflicts of Interest:** The authors declare no conflict of interest.
