Morphological and Biochemical Characterization of Bacterial and Viral Pathogens Infecting Mulberry Silkworm, Bombyx mori L.

A survey was under taken during the year, 2008 – 2009 in major silkworm growing regions of Tamil Nadu for collecting the location specific pathogenic strains of pathogens from flacherie and grasserie affected cadavers of mulberry silkworm, Bombyx mori L. The bacterial pathogens were isolated from the cadavers and purified in Nutrient Agar medium until the single pure colonies were obtained. For grasserie, virosed cadavers were macerated in a pestle and mortar, centrifuged and the pellets obtained were dissolved in sterile distilled water for obtaining the polyhedral occlusion bodies (POBs) of BmNPV. The pathogenic bacteria were identified based on morphological test, staining reactions, biochemical test and observation under the phase contrast microscope. The tests helped in identifying the pathogens as Bacillus thuringiensis, Bacillus cereus, Streptococcus faecalis, Staphylococcus albus and Staphylococcus aureus. For characterization studies of BmNPV, the microphotographs of the five BmNPV strains were made using the image analysis software by observing under oil immersion of phase contrast microscope. The BmNPV strains showed variation in the size of polyhedra. The diameter of different strains of BmNPV varied from 5.78 to 15.28 microns.