The silkworm, Bombyx mori is infected by a number of viruses: Bombyx mori nuclear polyhedrosis virus (BmNPV), cytoplasmic polyhedrosis virus (CPV), infectious flacherie virus (IFV) and densonucleosis virus (DNV). Except DNV, resistance of silkworms to the virus is controlled by polygenes. Serologically, two DNV types, DNV-1 and DNV-2 are identified. The non-susceptibility to DNV types is confer...