Enzyme Response in Thermotolerant Silkworm Breeds under Beauveria bassiana Infection

A study on enzyme activity in thermotolerant bivoltine silkworm breeds under Beauveria bassiana disease was conducted at the Department of Sericulture, UAS, GKVK, Bengaluru during 2021-23. Thermotolerant bivoltine breeds viz., B1, B4 and B8, were resistant to muscardine and CSR4, a muscardine susceptible breeds were used in this study. A batch of silkworms of all the breeds were inoculated with 6.86 × 104 spores / ml of B. bassiana @ 0.5 ml per silkworm immediately after 4th moult and another batch were reared under normal condition. The haemolymph was collected from these breeds at 48, 96 and 144 hours post inoculation (hpi) with B. bassiana spores in both inoculated and control batches. Biochemical estimation of amylase, protease and trehalase enzyme activities in the haemolymph. The amylase activity increased from 48 hpi to 144 hpi in all the breeds under both control and muscardine inoculation, but being lesser under inoculation. The protease activity was found higher in B1 breed from 48 hpi to 144 hpi under both control and inoculated conditions. Trehalase activity was enhanced at all time intervals under control conditions in B1, B4 and B8 breeds and CSR4 breed shows decreased at 144 hpi under both control and inoculation conditions. Thus increased enzyme activity in B1 and B4 breeds could be associated with their better performance for survival and economic parameters under inoculated condition. The correlational studies revealed that haemolymph amylase, protease and trehalase were found to be positively corelated with cocoon weight (g) and negatively correlated with larval mortality (%). Thus, the study revealed that silkworm breeds like B1, B4 and B8 as productive breeds and hence may be used for future breeding programmes for evolution of new robust silkworm breeds.