Research article IMPACT OF A NEW MICROSPORIDIAN INFECTION ON LARVAL AND COCOON PARAMETERS OF THE SILKWORM, BOMBYX MORI L.

Microsporidiosis is an important disease of silkworm caused by pathogenic microbes belonging to Phylum microsporidia. Various workers have isolated a number of microsporidia from silkworm. Recently, a new microsporidian was isolated from the silkworm by the authors of the present study. The microsporidian spores were studied for their morphology, pathogenicity and the transmission. These characters of the new microsporidian were compared with that of Nosema bombycis spores, a standard strain causing Pebrine disease in silkworm. The purified spores isolated from the silkworm were ovo-cylindrical in shape and measured 4.03 ± 0.24 µm in length and 2.30 ± 0.14 µm in width with 1: 0.57 length width ratio. In contrast, the spores of Nosema bombycis were oval in shape and were 3.80 ± 0.01µm in length, 2.60 ± 0.01µm in width and 1: 0.68 length width ratio. At the inoculation doses of 1 ×10 3 and 1×10 4 spore/ml, the infection rate in the moths was found to be 3.00 and 8.67 % with new microsporidian and N. bombycis respectively. At subsequent high inoculation doses 29.00 to 63.00 % infection at moth stage was recorded. The microsporidian has resulted in low larval and pupal mortality but remarkably high infection percentage in moth stage at 1×10 5 and 1×10 6 spore/ml inoculation doses. Studies also indicated that infection by the new microsporidian in mother moth did not impact the larval health and cocoon parameters in the next generation. In case of Nosema bombycis, cocoon parameters were significantly affected as the inoculum dose increased from 1 ×10 3 to 1 ×10 6 spores/ml. The larvae hatched from the eggs laid by Nosema bombycis infected moths (20 and above spores/field) did not survive up to cocooning. The results have been discussed in light of the studies carried out.