<p>Tropical tasar sericulture is an important livelihood for tribal communities in North and Central India, where the tasar silkworm (<i>Antheraea mylitta</i> D.) is reared in outdoor condition on host plants (<i>Terminalia arjuna</i> and <i>T. tomentosa</i>). However, outdoor rearing exposes silkworms to various pathogens, resulting in significant crop losses and adversely affecting the livelihoods of these communities. Effective disease management and the identification of emerging pathogens are essential for improving the productivity and profitability of tasar sericulture. This study reports the isolation and characterization of a novel bacterial pathogen, SBP-1, from diseased second instar larvae. Pathogenicity of isolated strain was confirmed through Koch’s law. The pathogen was identified through 16S rRNA gene sequencing, showing &gt; 99% similarity to <i>Serratia nematodiphila</i> strain PDRT. Morphologically, SBP-1 colonies were tiny, slimy, raised, circular convex, and creamy on nutrient agar, with cells being gram-negative, rod-shaped, and rounded at the ends. SBP-1 exhibited high virulence, causing up to 96% mortality in second instar larvae and progressively lower mortality in third (11.1%) and fourth instars (4.4%). The pathogen induced septicemia-like symptoms in larvae when artificially fed, and its median lethal concentration (LC₅₀) was determined to be 0.676 × 10⁵&#xa0;cfu/ml. This study is the first to report bacteriosis characterized by septicemia symptoms in tropical tasar silkworms and to identify <i>Serratia nematodiphila</i> strain SBP-1 as the causative agent. Its high virulence highlights the need for targeted disease management strategies and constant surveillance to identify and mitigate emerging pathogens to ensure sustainable tropical tasar sericulture.</p>