Isolation and evaluation of indigenous entomopathogenic fungi against larvae of fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW) (J.E. Smith) is a destructive and polyphagous agricultural pest worldwide. Non-target effects of synthetic insecticides being used extensively against FAW necessitate looking for biorational pest control options such as entomopathogenic fungi (EPF). Nevertheless, EPF conidia are sensitive to high temperatures and low humidity. This study evaluated the effectiveness of two indigenous EPF strains (Beauveria bassiana Bals. and Metarhizium anisopliae Metschn.) against FAW larvae under laboratory, screenhouse, and field conditions. Our laboratory bioassay showed that the highest concentrations (1.0 × 10⁹ conidia mL^-1) of both EPF exhibited the highest larval mortality (i.e., 86.66 and 73.33% by B. bassiana and M. anisopliae, respectively), and these were further formulated with 1.5% (w/v) sodium alginate hydrogel beads (SAHBs) by adsorbing 40 mL of conidial concentration in 1.0 g of SAHBs. The results showed maximum larval mortality by B. bassiana SAHBs (93.33%), B. bassiana alone (73.33%), and M. anisopliae SAHBs (66.66%) at 10 DAT in our laboratory bioassay. Under screenhouse conditions, maximum mortality of FAW larvae was observed by B. bassiana SAHBs (86.66%), B. bassiana alone (66.66%), and M. anisopliae SAHBs (66.66%) at 10 DAT. Furthermore, under field conditions, B. bassiana SAHBs exhibited maximum larval mortality (80%) on maize plants artificially infested with 3^rd instar lab-reared FAW larvae, followed by M. anisopliae SAHBs (60%) at 10 DAT. These findings validate the effectiveness of EPF conidia when formulated with SAHBs as a safe and eco-friendly strategy against FAW and other lepidopterous larvae.