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.

The deformed wing virus (DWV) is one of the most prevalent virus in honey bee colonies. The high prevalence of DWV is likely correlated to its ability to be transmitted by the mite Varroa destructor. PCR amplification of DWV negative RNA strands in mites and the tremendous DWV loads recorded from mites argue for the replication of DWV in both varroa and bees. Besides, there is strong evidence that DWV is also transmitted either horizontally by food exchange or vertically through eggs. DWV RNA loads measured in 360 seemingly healthy bee colonies from pools of 100 bees using quantitative PCR showed that bee colonies can tolerate very high loads of viruses without external clinical signs. We further identified DWV RNA in several bee organs by in situ hybridization and showed that queen and drone fertility could be impaired by such infection. In queen, the fat body cells were particularly infected while in drone, the whole reproductive reacted positively to DWV probe. Moreover, in crippled winged individuals from where very high DWV RNA genome copies were recorded, the digestive tract was heavily infected, indicating a probable negative effect on the digestive function. Our data strongly support that DWV produces pathogenic effects in severely infected individuals from the colony but these deleterious effects might not always have an impact on the colony fitness