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One of the major constraints in silk production is the diseases in silkworm rearing .Silkworm Bombyx mori is domesticated for silk production and are reared in colonial forms. A code of conduct for rearing silkworm is practiced to ensure survival of silkworm and cocooning.

All the major pathogenic microbes cause disease in silkworm and the most common among them are nuclear polyhedrosis , bacterial and viral flacherie, muscardine and pebrine. Nuclear polyhedrosis is caused by a baculovirus  Bombyx  mori nuclear polyhedrosis virus (BmNPV, Bcauloviridae). The viral flacherie is caused by Bombyx mori infectious flacherie virus (BmIFV, Picarnaviridae), Bombyx mori densonucleosis virus (BmDNV, Parvovoridae) and Bombyx mori cytoplasmic polyhedrosis virus ( BmCPV, Reoviridae) . Bacterial flacherie are caused primarily by serretia marcescens, Streptococcus sp, and Staphylococcus sp of bacteria. Muscardine is caused normally by Beauveria bassiana and Spicaria prassina. Pebrine, a dreaded uncommon disease is caused by Nosema bombycis, and several other microsporidians Variomorpha, Pleistophora, Thelophania, etc.

 

Disease Occurrence and the Estimated Loss due to Diseases

Survey on the prevalence of diseases in silkworm in different sericulture areas have been conducted during  different seasons of the past couple of decades. An estimated cocoon loss of 12-15 kg/ 100 dfls has been reported A loss of 35 million Rupees was estimated by Central Silk Board, India when muscardine was rampant during 1974-75 in Karnataka, India (Anon.,1975). Pebrine disease was on rampage in 1991-92 causing crop loss of over 2000 million Rupees.

Among the diseases, the point prevalence of nuclear polyhedrosis, in final instar, is reported to be 1.16% in winter, 2.34% in summer and 1.52% in rainy seasons  while for the flacherie disease it is 0.92% during winter, 3.4% in summer and 1.23%  in rainy seasons. The point prevalence of muscardine  is 0.79% during winter, 0.03% in summer and 1.08% in rainy season ( Selvakumar et al., 2002). A survey has been conducted to determine the loss due to different diseases ( Patil et al 1993). The loss due to nuclear polyhedrosis was determined as 11.90+ 3.65% ,14.77+ 5.7% and 5.90+ 1.25% during summer, rainy and winter seasons. The loss due to flacherie and muscardine was 22.97+ 3.82% and 0.36+ 0.29%, 11.39 1.84% and 4.08+ 1.10% , and 6.29+ 09% and 12.51+ 6.92% during summer, rainy and winter seasons respectively.