Characterization and Virulence of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) Isolates from Ecologically Distinct Soils Against Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura (F.) infests over 380 plant species. Insecticide resistance and ecological risks underscore the need for biological alternatives. The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin offers effective, sustainable pest control. We isolated entomopathogenic fungi (EPF) from diverse soils and evaluated the effects of temperature and media on their growth and sporulation. We also assessed their pathogenicity against S. litura. Fungal infection stages in S. litura were analyzed using scanning electron microscopy (SEM). Based on morphological and molecular analyses, five fungal isolates (PT-01, PT-03, PT-04, PT-05, and PT-06) were identified as M. anisopliae. Optimal fungal growth and sporulation occurred at 25 ± 1 °C on Sabouraud dextrose agar (SDA) medium. All isolates were pathogenic, causing mortality ranging from 23.33 ± 2.11% to 70 ± 8.21%, depending on the conidial concentration. The LC50 values ranged from 5.55 × 106 to 2.01 × 1013 spores/ml, while LT50 values varied from 4.01 to 18.71 d. Of these isolates, PT-01 showed the lowest LT50 and highest mortality and was selected for evaluation on developmental stages and greenhouse bioassays. Exposure of S. litura from eggs to fifth larval instars to 1 × 108 spores/ml of PT-01 revealed stage-specific susceptibility, with first instars exhibiting the greatest mortality and fifth instars the least. Greenhouse trial on the third larval instar showed reduced mortality. Fungal infection stages were confirmed via SEM. These findings show strong biocontrol potential of PT-01 against S. litura and support further evaluation in field trials, formulation and integration into Integrated Pest Management (IPM) programs.