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AbstractAs the honey bee and bumble bee may suffer from the same or related microbial pathogens, cross contamination from commercially reared Bombusspp. to honey bees and wild bumble bees and vice versa is a major concern. Honey bee-collected pollen to feed commercially reared Bombusspp. is a potential risk. Nosemaspp. is a fungal pathogen in bees. In this study, we developed new quantitative detection tools based on the detection of RNA using a TaqMan-based RT-qPCR for Nosema ceranaeand Nosema apis, with extraction controls based on the actin gene of honey bees and bumble bees, respectively. These tools were subsequently applied to study the epidemiology of N. ceranae, a main disease in honey bees. We screened gamma radiation and cold treatment sterilisation for their efficacy to kill N. ceranaespores fed in sugar water and in pollen to honey bees and bumble bees, respectively. N. ceranaeinfection in adult bumble bees was checked. Spores passing the inter-alimentary track were found but no infection was observed. N. ceranaespores were fed to honey bees. Their presence and multiplication were demonstrated, showing the spores were both viable and infectious. Our results indicate that N. ceranaefound in honey bees cannot infect commercially reared bumble bees (Bombus terrestris) and, that gamma radiation effectively kills N. ceranae. The highly specific and sensitive molecular assays developed, were exploited to detect N. ceranaein pollen and faeces, which would allow more comprehensive epidemiological studies on this important pathogen.