Abstract
Tropical tasar Sericulture is an important livelihood avenue for tribal inhabitant of the North and Eastern Indian states. Tasar silkworm (Antheraea mylitta D.) is reared in natural condition i.e., outdoor on its preferred food plants i.e., Terminalia arjana and T. tomentosa. The outdoor rearing exposes silkworm to many diseases and prone to crop loss, this impacts significantly the livelihood of local inhabitants. To make the tasar sericulture more profitable, it is highly essential to provide effective disease management and constantly identify emerging silkworm pathogens. Keeping this in view, in present investigation SBP-1, a new bacterial pathogen was isolated from a naturally diseased second instar larvae, which is showing new symptoms and causing higher mortality. Pathogenicity of isolated strain was confirmed through Koch’s law. Pathogen was identified through 16S rRNA gene sequencing. Sequence analysis revealed that it has more sequence similarity (> 99%) with Serratia nematodiphila strain PDRT. The colony was tiny, raised, opaque, slimy, circular convex shaped with shining creamy colour on nutrient agar. Cells are gram negative, rod shape with round ends. SBP-1 strain mainly infect at young stage and causes high mortality up to 96% in second instar, however cause less mortality in later larval instars (11.1% in 3rd and 4.4% in 4th instar). SBP-1 produces septicaemia like symptoms when fed artificially to the healthy larvae. The median lethal concentration (LC50) of the pathogen was 0.676 × 105 cfu/ml. This is the first report on bacteriosis showing septicemia symptoms in tropical tasar silkworm and also the first report of S. nematodiphila strain SBP-1 causing septicaemia. Further studies are essential to design preventive and control measures against this highly virulent strain. Constant studies are required to identify unknown pathogens causing various bacteriosis symptoms in tropical tasar silkworm.