Supplementation of Lactobacillus casei reduces the mortality of Bombyx mori larvae challenged by Nosema bombycis

OBJECTIVE: Pebrine, caused by the microsporidium Nosema bombycis, is one of the severe diseases in Thai polyvoltine strains of the silkworm Bombyx mori. Studies showing the presence of Lactobacillus species in the silkworm gut, where the Nosema parasites enter, suggests that these bacteria may have a protective effect. The aim of this study was to investigate the effect of supplementation of Lactobacillus casei on the survival ratio of silkworm larvae challenged with N. bombycis. RESULTS: A group of silkworm larvae of the commercial Thai polyvoltine hybrid strain DokBua was supplemented with L. casei on the second day of the 2nd, 3rd, 4th, and 5th instar. When a control group of silkworm larvae were challenged with N. bombycis on the second day of the 4th instar, the survival rate was 68%, but it was 91% for larvae supplemented with L. casei. For those larvae that survived the treatments until pupation, we determined the growth characters larval weight, cocooning ratio, and pupation ratio, and the economic characters cocoon weight and cocoon shell weight. When infected with N. Bombycis, growth characters were significantly higher in larvae also receiving L. casei.