Co-Occurrence of the Nucleopolyhedrovirus and Bidensovirus in Silkworm, Bombyx Mori L.: Evidence from Kashmir and Molecular Comparison of Indian Bidensovirus Isolates

Abstract

The mulberry silkworm, Bombyx mori L. (Lepidoptera: Bombycidae), is an economically important insect domesticated for silk production in India and other countries, whereas the Bombyx mori nucleopolyhedrovirus (BmNPV) and Bombyx mori bidensovirus (BmBDV) are the two most serious viral pathogens infecting the domestic silkworms. In this study, the frequency of co-occurrence of BmNPV and BmBDV in silkworm larvae from sericulture practicing regions of North, Central, and South Kashmir was investigated. The prevalence of grasserie disease (%) and extent of cocoon crop loss varied significantly between the different regions. On the basis of PCR analyses, the mean co-occurrence (%) of BmNPV and BmBDV infection was 94%, 92.7% and 98% in the samples from North, Central and South Kashmir, respectively. The BmBDV isolates from Mysore, Andhra Pradesh, Tamil Nadu, Kashmir, Dehradun, Ghumarwin and Jammu grouped together and are most closely related to other BmBDV isolates on the basis of gene sequencing and phylogenetic analyses of the VD-1 gene fragments. The BmBDV-S1 isolate had the lowest LD50 and ST50 values revealing that it was more virulent to B. mori larvae as compared to BmBDV-N1 and BmBDV-C1 isolates. Overall, the results revealed that the BmNPV and BmBDV coexist in the silkworm larvae and highlight the need for greater research into the interaction of these viruses in Bombyx mori.