Natural anti-UV formulation increases the survival of Beauveria bassiana and Metarhizium rileyi conidia and enhances the biological control of Spodoptera frugiperda in corn plants

Abstract

Solar radiation (SR) decreases the effectivity of entomopathogenic fungi (EPF) propagules. The main objective was to evaluate a natural formulation (NF) based on humic acids (HA) with anti-UV effects, to improve the survival of conidia against SR, evaluating its capacity in the control (BC) of Spodoptera frugiperda. The strains used were Beauveria bassiana CHE-CNRCB 1029, Metarhizium rileyi CHE-CNRCB 682 and Metarhizium rileyi CHE-CNRCB 796. Compatibility evaluations (6.49, 9.51 and 12.39 mg/L of HA) were performed, as well as survival evaluations, anti-UV effects and pathogenicity bioassays (13.64, 20.45 and 27.27 AH mg/L). The two M. rileyi strains showed greater compatibility when comparing the radial growth rate (RGR) and the survival percentage (CFU). The anti-UV effect was positive when HA suspensions were mixed with conidia from the three strains evaluated. Conidia mixed with HA maintained virulence against S. frugiperda (L2) larvae. Mortality by the spraying method for B. bassiana reached 66.66%, and 86.66% for both M. rileyi strains, while by the immersion method, it reached 73.33% for B. bassiana and between 85.71% and 87.03% for the M. rileyi strains, respectively. The persistence of conidia B. bassiana and M. rileyi increased under exposure to SR when mixed with an NF with anti-UV effects, maintaining its virulence against S. frugiperda. This finding represents an attractive alternative during the formulation of EPF.