Abstract: 【Objective】The objective of this study is to define the infectivity and pathogenic mechanism of Nosema ceranae to Bombus patagiatus. 【Method】 Traditional biology and ultrastructure under electronic microscope methods were used, and combined with the quantitative real-time PCR (qPCR) to explore the pathogenesis of N. ceranae to B. patagiatus. 【Result】 In the initial infection, the infected bees did not exhibit obvious external disease signs except decreased feeding and motor retardation. In the late period, the infected bees exhibited dispirited, weak and unable to fly. Through observation with light microscope, few N. ceranae but a lot of bacteria were found in the midgut of bees. N. ceranae mainly infected midgut of epithelial cells, the nuclear enlarged and out of shape, mitochondria become smaller even disintegrating and endoplasmic reticulum become disorders. However, the spores only infected the cytoplasm of the host instead of invading the nuclear, which lead to the disintegration of the mitochondria and cytoclasis. Quantitative analysis on RT-PCR showed that N. ceranae reached the highest level in the midgut and fat body 3-4 d after being infected and other organizations were barely detected.【Conclusion】N. ceranae can cross-species infect B. patagiatus and the pathological process starts with the pathological changes of intestinal cells, which lead to the cytoclasis and apoptosis.

Key words: Bombus patagiatus , Nosema ceranae , ultrastructure , qPCR