Isolation and Characterization of Indigenous Nucleopolyhedrovirus Infecting Fall Armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) in India

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an invasive insect pest of maize in India. Natural occurrence of nucleopolyhedrovirus (NPV) infection on S. frugiperda larvae was recorded in 2018 during surveys conducted in maize fields in Chikkaballapura district of Karnataka, and Coimbatore and Tirupattur districts of Tamil Nadu. A strain of S. frugiperda nucleopolyhedrovirus (SpfrNPV NBAIR1) infecting S. frugiperda was isolated from the diseased larvae; morphological and biological characteristics were studied. Electron microscopic studies showed tetrahedral-shaped SpfrNPV occlusion bodies (OBs) of size 1.64 μm. Dose–mortality bioassays revealed that first, second and third instar larvae were equally susceptible (LC₅₀ 3.71–5.02 OBs/mm²) to SpfrNPV infection. A PCR technique for detection of viral DNA in S. frugiperda NPV was developed by employing the polyhedrin gene (polh)-specific primers. The amplicon of 618 bp was amplified, sequenced and NCBI GenBank accession number was obtained (MT422725). Blast analysis revealed that SpfrNPV conserved polh gene sequence matched 100% with the reference GenBank sequence (J04333) from the NCBI database which confirmed the identity of the SpfrNPV.