The mulberry silkworm Bombyx mori (L.) (Lepidoptera: Bombycidae) is infected with a baculovirus, Bombyx mori nucleopolyhedrovirus (BmNPV) that causes grasserie disease in silkworm and major economic losses to the silk industry. In India, >50 % of silk cocoon crop losses are attributed to BmNPV infection. Presently, there are no specific preventive measures for the occurrence and spread of BmNPV infection other than sanitized rearing methods, the only commercial practice today is to discard large stocks of worms in case of infection. Although diagnostic kits for detection of BmNPV have been developed, they are not extensively used on a commercial scale and subsequently, they fail to provide the indispensable and timely advantages desired for early disease intervention. The best emerging technology is the use of antibody-based biosensors and lateral flow assays, which have high specificity, sensitivity and the option of "onsite" pathogen detection. The use of disease resistant silkworm breeds or the utilization of inherent resistance in silkworm would be the most economical and effective way to prevent the occurrence of grasserie disease. Further, there is a great need to comprehensively analyze the host genes response to BmNPV infection and its functional analysis to prevent virus replication and its horizontal transmission.

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.

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