Isolation and Evaluation of Indigenous Isolates of Beauveria bassiana and Synergistic Control of Spodoptera frugiperda with the Parasitoid Microplitis prodeniae

Entomopathogenic fungi (EPFs) are capable of infecting a variety of insect pests and are widely used as biopesticides worldwide. This study intended to isolate indigenous EPFs from cadavers of <i>Protaetia brevitarsis</i> and investigate their effects on the fall armyworm <i>Spodoptera frugiperda</i> (FAW), a globally widespread invasive pest. Morphological and molecular analyses confirmed four native EPF strains all belong to <i>Beauveria bassiana</i>. Pathogenicity tests showed they were virulent toward FAW 1st instar larvae. The application of EPFs either by dipping or spraying significantly increased the larval mortalities compared to the control group, with corrected mortalities ranging from 92% to 73% after dipping in a fungal suspension of 10⁸ conidia/mL, and those ranging from 76% to 35% after spraying with a fungal suspension of 10⁷ conidia/mL. Our findings revealed the infectivity of four strains to FAW larvae significantly changed in a dose- and time-dependent manner. In addition, the combination use of the local <i>B. bassiana</i> strain and parasitoid <i>Microplitis prodeniae</i> resulted in a significantly enhanced <i>S. frugiperda</i> 3rd instar larval mortality compared to a single inoculation with one of them, suggesting an apparent synergistic effect for the joint application of these two biological control agents. The mortality inflicted by <i>B. bassiana</i> was probably promoted by the release of parasitoids, since the parasitoids' movements and attacks could strengthen the fungal distribution and infection processes. This study underscores the potential of the combination use of EPFs and parasitoids against <i>S. frugiperda</i> early-instar larvae, and provides insights into the consequences of integrating these EPFs into integrated pest management systems.