41st Annual Meeting of the Society for Invertebrate Pathology
and 9th International Conference on Bacillus thuringiensis

Phylogenetically, Microsporidia are now considered highly specialised parasitic fungi. They are all intracellular parasites with a characteristic and unique mode of infection. Microsporidia may infect all life forms and undoubtedly, only a small fraction of the actual number of species have been characterised. In Hymenopteran pollinators, microsporidia infections have been described from four host species only: Nosema apis infecting the European honey bee, Apis mellifera; Nosema ceranae infecting the Asian honey bee, Apis cerana; Nosema bombi, infecting Bombus spp. and Antonospora scoticae infecting Andrena scoticae. N. apis and N. ceranae are cross infective between hosts. However, N. apis does not do well in A. cerana, whereas there is a worldwide process of N. ceranae replacing N. apis in A. mellifera. N. bombi has recently become of particular interest for conservationists, since this parasite may be distributed to areas assumed free from this parasite, thereby presumably endangering endemic bumble bee spp. Furthermore, within-genome rRNA variability in N. bombi suggests that to characterize intraspecific genetic variants in the Microsporidia based on RNA sequences is not straight forward. A. scoticae infects the fat body tissue of A. scotica and may occur with an extreme prevalence in its host.

Nosemosis in western honey bees (Apis mellifera) is caused by the microsporidians Nosema apis and N. ceranae. Pathology associated with N. apis, the historical parasite of western honey bees, is well understood, and includes increased winter mortality and poor spring build-up of surviving colonies. Conversely, pathology associated with recently-detected N. ceranae, historically of Asian honey bees (Apis cerana), is not well-described. N. ceranae was associated with increased winter mortality and reduced honey yields in Spain, and was highly pathogenic when inoculated experimentally. The antibiotic fumagillin dicyclohexylammonium (hereafter, fumagillin) is used to control N. apis; however, it is unclear whether fumagillin is effective against N. ceranae. To determine this, western honey bee colonies in Nova Scotia, Canada were sampled in spring and late summer 2007. Nosema intensity in the spring was significantly lower in colonies treated with fumagillin in September 2006 (n = 94) than those not treated (n = 51), but by late summer no difference existed between groups. Molecular sequencing of 15 infected colonies identified N. ceranae in 93.3% of cases, suggesting that fumagillin is successful at temporarily reducing this recent invasive parasite in western honey bees.