Pathogenicity, ultra-structural growth and development of green muscardine fungus, Metarhizium anisopliae (Metschnikoff) Sorokin (Ascomycota: Hypocreales) on maize fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

Abstract

Abstract Background The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) is a devastating pest of maize, difficult to manage using a single pest management tactic. The entomopathogenic fungus (EPF), Metarhizium anisopliae being an eco-friendly component, could be an effective tool for managing this notorious pest owing to its preferred habitat, principally the whorl region. Results Metarhizium anisopliae (TNAU-MA-GDU) isolated from FAW was evaluated against 2nd instar larvae of S. frugiperda reared under laboratory conditions. The pathogenicity and infection process were also studied through scanning electron microscope (SEM). The LC50 value for M. anisopliae isolate TNAU-MA-GDU was recorded as 5.8 × 104 spores ml−1 against the second instar larvae of S. frugiperda. SEM observations on the infection process revealed the adherence of the conidia on the head, cuticular ornamentations of the thorax, sensory seta, and legs at 24 h post-infection (hpi). Formation of germ tube and appressoria was observed from 48 hpi with subsequent hyphal development at 72 hpi. Complete networking of mycelium and conidiogenesis observed after 168 hpi. Conclusion An understanding of fungal–host interactions at the ultramicroscopic levels could reform present tactics for developing hyper-virulent EPF strains.

Keywords

• Spodoptera frugiperda
• Metarhizium anisopliae
• Bioassay
• Scanning electron microscope (SEM)