Infectivity of Nosema ceranae isolates from different hosts and immune response in honey bees Apis mellifera and Apis cerana

The microsporidium, Nosema ceranae, was first discovered in Apis cerana. Currently, N. ceranae is a highly prevalent parasite in A. mellifera colonies worldwide. The pathology of N. ceranae and how bees defend themselves from this pathogen have been reported. Here, we investigated the infectivity of two N. ceranae isolates from different honey bee species, A. mellifera and A. cerana. Our results showed that the N. ceranae isolate from A. mellifera had a significantly higher infectivity than another isolate from A. cerana in all experimental cages of A. mellifera and A. cerana. Moreover, when comparing the infectivity of each N. ceranae isolate between the original and new hosts, it seems that no significant difference was obtained. The immunity-related enzymes in honey bees following N. ceranae inoculation were also analyzed at day six after spore feeding. Phenol oxidase (PO) transcript levels were up-regulated in A. cerana when inoculated by both N. ceranae isolates, but were not significantly different. However, the transcript level for PO in one experimental cage of A. mellifera was significantly down-regulated when inoculated with N. ceranae. Significant glucose dehydrogenase suppression occurred in only one cage of each honey bee species.