Characterization and field evaluation of tetrahedral and triangular nucleopolyhedrovirus of Spilosoma obliqua (SpobNPV) strain NBAIR1 against jute hairy caterpillar

Jute hairy caterpillar, Spilosoma (=Spilarctia) obliqua (Walker) (Arctiidae: Lepidoptera), is an irregular and polyphagous insect pest that occurs all over India. A severe natural viral epizootic was observed in the field population of S. obliqua in jute. The virus was characterized as Spilosoma obliqua nucleopolyhedrovirus (SpobNPV NBAIR1) based on morphological, biological, and molecular characterization. Under scanning and transmission electron microscopy (SEM and TEM), the occlusion bodies (OBs) of SpobNPV NBAIR1 appeared as both tetrahedral and triangular with the size ranged from 1.04-1.72 μm. The results on the bioassay studies revealed that the lowest LC50 value of 2.93 OBs/mm2 by leaf disc bioassay against the second instar S. obliqua showed its high virulence. The identity of SpobNPV was further confirmed by the amplification of polyhedrin gene (NCBI GenBank accession no. MK288145). Eleven species of lepidopteran insects, viz., Spodoptera litura, S. exigua, S. frugiperda, Helicoverpa armigera, Plutella xylostella, Amsacta albistriga, Maruca vitrata, Trichoplusia ni, Pieris brassicae, Agrotis ipsilon, and Bombyx mori, were not susceptible to the infection with SpobNPV NBAIR1. Field experiments on jute crop revealed 68.92, 78.59, and 93.16% reduction in larval population of S. obliqua at 3, 4, and 7 days post spray of SpobNPV NBAIR1 (1.5 × 1012 OBs/ha at 2 ml/l), respectively. The present study is a renewed effort in the management of S. obliqua by the new strain of SpobNPV NBAIR1.