Abstract: 【Aim】 To identify the morphological and molecular characteristics of microsporidium Nosema sp. CP isolated from Catopsilia pyranthe， and then to assess the infectivity and transmissibility of this Nosema sp. CP in the domestic silkworm， Bombyx mori. 【Methods】 After purification of Nosema sp. CP spores isolated from wild C. pyranthe butterflies， the shape， sizes and axial ratios of the spores were measured under the microscope， respectively. The DNA fragments of 16S rDNA from this microsporidian species were amplified by PCR and then sequenced to confirm its classification status. The Nosema sp. CP isolated and N. bombycis was fed respectively to B. mori larvae of day-1 2nd instar and day-1 4th instar to survey the infectivity and transmissibility via embryo during different developmental stages of B. mori. 【Results】 Oblong shape and diplokaryotic nuclei of the isolated microsporidia in this study were visualized under the microscope. Molecular analysis of 16S rDNA sequence showed more than 99% identity to that of the previously reported microsporidian spores isolated from C. pyranthe. The total infection rates of Nosema sp. CP and N. bombycis to B. mori were 68.8% and 98.3%， respectively. In the second generation of B. mori after vaccination， the detection rates of sporozoans of Nosema sp. CP and N. bombycis in newly-hatched larvae were 100% and 100%， and those of their eggshells were 92.9% and 100%， respectively. The embryo transmissibilities of Nosema sp. CP and N. bombycis to B. mori were 9.6% and 23.2%， respectively. 【Conclusion】 The microsporidia isolated in this study are Nosema sp. CP and have typical characteristics of Nosema diplokaryotic nuclei. The Nosema sp. CP isolated can infect B. mori and has transmissibility via embryo in this insect. However， in B. mori both the infection rate and transmission rate of Nosema sp. CP isolated in this study are lower than those of N. bombycis. Thus， it is necessary to prevent and control the prevalence of Nosema sp. CP in sericultural industry.

Key words: Nosema, Nosema sp. CP, Bombyx mori, morphology, molecular identification, infectivity, transmissibility