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A number of viruses are known to cause the disease in mulberry silkworm, Bombyx mori L. and cause significant cocoon crop loss to the farmers. The study has been undertaken to assess the prevalence of silkworm viral diseases caused by B. Mori Nucleopolyhedrovirus (BmNPV), B. mori Infectious Flacherie Virus (BmIFV) and B. mori Densovirus1 (BmDNV1) through external symptoms and molecular characterization from different climatic regions of India. During the intensive exploratory surveys in 2017, silkworm larvae with typical symptoms of BmNPV, BmIFV and BmDNV1 were collected across seven provinces from North India [Kashmir (temperate), Jammu, Ghumarwin in Himachal Pradesh, Dehradun in Uttarakhand (subtropical) and South India [Karnataka, Andhra Pradesh and Tamil Nadu (tropical)]. Dissection of diseased specimens confirmed the presence of virus through anatomical changes viz, size, shape and colour of organs after disease attack. The viruses were isolated and identified through PCR amplification of highly conserved genes. The results reveal that BmNPV, BmIFV and BmDNV1 are evenly prevalent across India. The infection percentage of BmNPV, BmIFV and BmDNV1 in North India (11.41 ± 1.21, 7.81 ± 0.67 and 7.40 ± 0.61) was significantly higher than South India (1.61 ± 0.17, 1.52 ± 0.14 and 1.62 ± 0.14), respectively. The highest prevalence of these viruses was observed from subtropical followed by temperate and tropical climate. The knowledge of the prevalence of these viruses in India and their synergism with bacteria and influence of other possible factors is important for preventing cocoon crop losses caused by viral diseases in India.

The mulberry silkworm, Bombyx mori L., 1758 (Lepidoptera: Bombycidae) is classified as univoltine, bivoltine, and polyvoltine based on the annual brood frequency. Voltinism in B. mori is characterized by the occurrence of embryonic diapause (facultative and obligatory diapause). Univoltine silkworms suited to cold and temperate regions lay diapausing eggs and polyvoltine silkworms suited to tropical regions lay non-diapausing eggs. In contrast, the occurrence of diapause in bivoltine silkworms is influenced by the environment. In addition to the difference in the occurrence of embryonic diapause, larval duration, and cocoon characters show distinct variations. In the present correspondence, we are presenting an interesting observation from two silkworm races Barapath and Barapolu originating from the North-East region of India that display divergence in voltinism. The unique characteristic features of univoltine, bivoltine, and polyvoltine observed in the races are discussed explaining the occurrence.