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.

Mites in the genus Tropilaelaps (Acari:Laelapidae) are parasites of the brood of honey bees (Apis spp.). Tropilaelaps clareae is described from Apis dorsata, but the mite also parasitizes the European honey bee, Apis mellifera. Infestations can rapidly lead to the death of entire bee colonies and T. clareae is hence considered more dangerous to European bees than the parasitic mite Varroa destructor. Honey bees are infected by many different viruses, some of them associated with and vectored by V. destructor. The most prevalent virus infection in honey bees in recent years, associated with V. destructor appears to be deformed wing virus (DWV). DWV is distributed world-wide, and found wherever the Varroa mite is found. The Varroa mite transmits viral particles when feeding on the haemolymph of pupae or adult bees. Both the Tropilaelaps mite and the Varroa mite feed on honey bee brood, but no observations of DWV in Tropilaelaps have so far been reported. In this study, we used a novel quantitative real-time RT-PCR to investigate the occurrence of DWV in infested brood and Tropilaelaps mites collected in China. We can, for the first time, report occurrence of DWV in T. clareae and demonstrate a close association between mite-infested pupae of A. mellifera and DWV infections.

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.

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.

Ascosphaera apis is an important fungal pathogen of honey bees. A. apis produces sexual spores (ascospores) that are the primary infective agent of chalkbrood disease. Honey bee larvae can be infected with A. apis by ingesting larval food contaminated with ascospores. By contrast, asexual reproduction has never been described in A. apis, although it is a widespread form of propagation in Ascomycetes. Since asexual reproduction does not require mating, it allows rapid production of large numbers of conidia (mitospores), and their subsequent dispersal into new areas. This study thus fills an important gap in current understanding of the developmental cycle of an important fungal honey bee pathogen. Herein we describe asexual reproduction in A. apis and discuss its potential role in host pathogenesis and in the dissemination of this infectious bee disease in the environment. Considering the worldwide spread of chalkbrood disease and the lack of EPA approved drugs to cure it, an understanding of the A. apis life cycle is an important factor in the design of a disease management program.