Characterization and field evaluation of Spilosoma obliqua nucleopolyhedrosis virus (SpobNPV) CRIJAF1 strain against jute hairy caterpillar, Spilosoma obliqua (Walker) infesting jute, Corchorus olitorius Linn.

Abstract

Background: Spilosoma (= Spilarctia) obliqua (Walker) (Lepidoptera: Arctiidae), once considered as a sporadic pest, is now considered as a major and polyphagous pest widely distributed throughout India. Recent outbreaks of this pest were manifested in both jute and sunnhemp. During a survey in and around adjoining villages of I.C.A.R-C.R.I.J.A.F, Barrackpore, an epizootic was observed in the field population of S. obliqua caused by a nucleopolyhedrosis virus. Hence, an attempt was made to isolate, characterize using electron microscopy and assess the efficacy of S. obliqua nucleopolyhedrosis virus under laboratory and field conditions. Results: Electron microscopic studies revealed typical baculovirus occlusion bodies of type nucleopolyhedrosis virus with tetrahedral and triangular in shape with the size ranging from 2.55 to 2.90 µm, with an average size of about 2.72 µm. Bioassay studies showed the larval mortality at low concentration of SpobNPV, i.e., 2.42 × 104 POBs/ml. The virus-infected S. obliqua was identified through the amplification of polyhedrin, polh gene sequences with the available sequences in public database, GenBank, NCBI. The sequence data generated for the polyhedrin gene were deposited in GenBank, and accession number was obtained, MN648213. Field experiment revealed 50.52, 63.25 and 82.91% larval reductions, respectively, at 2, 4 and 7 days after spray of S. obliqua nucleopolyhedrosis virus. Conclusion: The present study revealed that foliar application of S. obliqua nucleopolyhedrosis virus was very effective in causing mortality against S. obliqua larvae and thus can be used as an effective microbial bioagent in the integrated pest management of the caterpillar, S. obliqua.