1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502324, Andhra Pradesh
2All India Networking Project on Betel vine, Bapatla-522101, Andhra Pradesh
3Acharya Nagarjuna University, Nuzvid Campus, Nuzvid-521201, Andhra Pradesh
*Current address: International Institute of Tropical Agriculture (IITA), PMB 5320, Ibadan, Nigeria.
Helicoverpa armigera (Hubner) (Noctuidae: Lepidoptera), commonly known as legume pod borer, is a major insect pest of legume crops in the semi-arid tropics. A baculovirus of type nucleopolyhedrovirus (NPV) was isolated from this insect during natural epizootics at ICRISAT, Patancheru (Andhra Pradesh, India). Electron microscopic studies showed that the occlusion bodies (OBs) are in polyhedral shape and approximately 2 μm in diameter containing multiple nucelocapsids per envelope and purified virus particles revealed bacilliform to cylindrical shaped structures of size of 282 × 49 nm. In bioassays the virus on 2nd and 3rd instar H. arimigera larvae had LC50 values on 7th day are 2.30 × 104 and 1.5 × 105 POBs/ml and LT50 values at virus concentration of 1.8 × 107 POBs/ml are 118.80 and 133.92 hr respectively. The virus yield was high in the field-collected larvae (5.60 × 109 POBs/larva and/or 14.01 × 109 POBs/ml) than laboratory reared larvae (5.02 ×109 POBs/larva and/or 12.42× 109 POBs/ml), but no variation in their virulence (LC50 values on 7th day: 1.79 × 105 and 1.11 × 105 POBs/ml). Using a degenerate oligonucleotide primer set polyhedrin gene of the virus was amplified by PCR. This resulted in a 744 bp product which was cloned and sequenced. The nucleotide gene sequence had a high homology with several NPVs, specifically with NPV from Mamestra brassicae (97%), Mamestra configurata (97%) and Leucania seperata (95%) (Noctuidae: Lepidoptera) and these three viruses shared a unique restriction site for Xho-1 enzyme at nucleotide position 130 (M. brassicae and M. configurata) and at 670 (L. seperata). The phylogenetic analysis showed that the virus belongs to Group-II NPVs and the virus was named as Helicoverpa armigera Nucleopolyhedorivrus (NPV), Patancheru strain. This is the 8th report worldwide and first report from the Indian subcontinent to be described the complete polyhedrin gene of a NPV isolated from H. armigera. Field efficacy studies of this virus (250 LE/ha) against H. armigera on chickpea crop was comparable with fields sprayed with a synthetic insecticide (endosulfan at 0.07%) confirming its usefulness for controlling legume pod borer.
