PREVALENCE OF FLACHERIE DISEASE AND PATHOGENICITY OF ISOLATED PATHOGENS IN SILKWORM, BOMBYX MORI (L.) UNDER DIFFERENT ENVIRONMENTAL CONDITIONS

Flacherie is one of the diseases in silkworm caused by different bacteria and viruses. Flacherie diseased silkworm larvae were collected from different sericultural areas of Karnataka during different seasons and the pathogens were isolated. The data revealed that prevalence of flacherie was high in summer (5.0 – 20.0%) followed by rainy (2.5 – 15.0%) and winter (0.0 – 7.5%) seasons. It was also observed that the flacherie larvae were infected individually with bacteria (7.5 – 20.0%) or viruses (0.0 – 17.5%) and combined infections of both (5.0 – 32.5%). Streptococcus faecalis Andrewes and Horder, Staphylococcus aureus Rosenbach, Serratia marcescens Bizio and Bacillus thuringiensis Berliner were found pathogenic to silkworm. BmIFV and BmDNV1 were detected in the midgut larval samples and BmNPV was noticed in very few haemolymph samples. LC50 value was calculated for the pathogenic bacteria viz., S. faecalis, S. aureus and S. marcescens under three different environmental conditions (E1, E2 and E3) and the LC50 value against these bacteria was 5.5 × 107, 3.3 × 108 and 6.1 × 108 cells/ml, respectively at E3. LC50 could not be made for the above bacteria at E1 and E2 environment as there was less than 50% mortality even in high concentration. In the case of B. thuringiensis, the mortality was due to toxicity and the LC50 value was 3.2 × 106, 2.8 × 106 and 2.4 × 106 cells/ml at E1, E2 and E3, respectively. LC50 was also calculated against all the viruses (BmIFV, BmDNV1 and BmNPV) and it was 10-4.8 dilutions, 10-2.9 dilutions and 2.0 × 105 polyhedra/ml (E1), 10-4.9 dilutions, 10-3.1 dilutions and 1.1 × 105 polyhedra/ml (E2) and 10-5.1 dilutions, 10-3.6 dilutions and 5.0 × 104 polyhedra/ml (E3), respectively.