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

In North America, populations of the honey bee Apis mellifera have been in decline since the introduction of the varroa mite, Varroa destructor, in the 1980's. Parasitization by varroa mites still is a major factor underlying most colony losses, most likely through immunosuppression and increased disease instance. However, a new phenomenon was identified in late 2006 that is though to be responsible for large colony losses in affected apiaries: colony collapse disorder (CCD). This condition is identified by a set of unique symptoms: no dead bees in the affected hive or apiary, honey bee brood and food stores are left behind, and secondary pests hesitate to invade affected hive equipment. CCD has continued to have major impact on bee colonies in the United States and significantly add to the already high loss of colonies due to varroa parasitization. In an attempt to determine the cause or causes of CCD, several studies were initiated. Common samples were collected from CCD and non-CCD affected apiaries and shared among various institutions in an attempt to isolate a single causes. No one culprit has yet been found which explain all CCD losses. A longitudinal epidemiological study was also initiated in 2007 that followed individual colonies over time, sampling them repeatedly. This study uncovered several factors which impact bee health but not necessarily how CCD is triggered. This presentation will discuss the approaches being taken to investigate causes of colony losses, and how losses in the United States compares to losses in other countries in terms of magnitude, symptoms and response.

Nosema ceranae is a worldwide parasite of honey bees that has shown dramatic range expansion in recent years. N. ceranae levels can be quantified using qPCR with both ribosomal and protein-coding genes, and we are using these techniques along with histology to clarify the interactions between this pathogen and bee hosts. An analysis of honey bee samples collected between 1995 and 2007 from 12 U.S. states showed that N. ceranae has surpassed congener N. apis as the predominant microsporidian infection of A. mellifera in the U. S. Tissue tropism of N. ceranae in the host was quite different from that of N. apis. Specifically, while N. apis is largely confined to the gut epithelium, N. ceranae was found not only in the primary infection site, the midgut, but also in the hypopharyngeal glands, salivary glands, Malpighian tubules and fat body. The complex biological features and disease importance of N. ceranae in honey bees invite further research. New tools for measuring gene expression and an effort to sequence and annotate the N. ceranae genome should help clarify the means by which this microsporidian affects honey bee health, and the counter-defenses used by bees.

Honey bee colonies face disease threats ranging from viruses to bacteria and mites. Recent severe colony losses in North American honey bees reflect, in part, a rare syndrome during which adult bees disappear from colonies, leaving behind healthy queens and brood with no obvious pathologies. Current hypotheses to explain this syndrome, Colony Collapse Disorder, center on nutritional deficiencies in bees, exposure to harmful exogenous chemicals, and the presence of new or resurgent pathogens. These hypotheses have been tested by genetic analyses of honey bee pathogens and gene-expression analyses of honey bee genes involved in immunity and stress responses. Copy numbers of several bee viruses as well as trypanosomatid parasites are positively correlated with CCD, with a substantial geographic component to the predominant pathogens. Several honey bee genes have emerged as expression biomarkers for CCD, although CCD and control bees do not show systematic differences in the expression of genes related to immune function or stress responses. Genomic resources for honey bees and their major pathogens are also being used to improve honey bee breeding and management for disease resistance. Heritability and efficacy of immune genes targeting the bacterial pathogen Paenibacillus larva will be discussed, along with efforts to use molecular tools to follow bee-bacterium interactions.

Among the social insects, honeybees Apis mellifera have an exceptionally diverse set of parasites and pathogens. In this study two species of fungal diseases have been investigated: one is the common brood diseases, chalkbrood (Ascosphaera apis) and another opportunistic, but less common pathogen in honeybees, the stonebrood (Aspergillus flavus). Using the honeybee larvae as host and these two pathogens we investigated in vitro temperature impacts on the infected larvae. Temperature is known to have a crucial role in mediating the outcome of the host – parasite interactions; however there is limited information on the possible competition among fungal pathogens within the honeybee host. In addition, we investigated within-host competition among different fungal pathogens within a single larva and the role temperature plays in mediating these interactions.

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.