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

RNA viruses are emerging as a serious threat to honey bee (Apis mellifera) health and are suspected as major contributors to the recent malady, Colony Collapse Disorder. Understanding the transmission of these viruses can shed valuable light on the epidemiology of this syndrome. In addition, the recent detection of Deformed Wing Virus in bumble bees as well as some of these viruses in in-hive food reserves of honey bees suggests a possible wider environmental spread of viruses with potential impact on the overall pollinator community. We studied the distribution of viruses in honey bees, their pollen loads and in other non-Apis hymenopteran pollinators collected from flowering plants. All the samples were analyzed with reverse transcriptase-PCR and virus identity was confirmed by sequencing. We report for the first time the molecular detection of picorna-like RNA viruses (deformed wing virus, sacbrood virus and blackened queen cell virus) in pollen pellets collected directly from forager bees. Furthermore, pollen pellets from some uninfected foragers were detected with virus, indicating a potential role of pollen in viral transmission. These viruses were found in eleven other species of native bees and wasps, expanding the known host range of these viruses and suggesting a possible deeper impact on the health of our ecosystem. Sequence comparisons of viruses isolated from honey bees, pollen and other non-Apis hymenopteran species indicate that the viruses are circulating freely among these species. In addition, the Israeli Acute Paralysis virus was detected in non-Apis pollinators near CCD apiaries but not in those near healthy non-CCD apiaries. Our findings increase the understanding of virus epidemiology and may help explain bee disease patterns and pollinator population decline.

Israeli acute paralysis virus (IAPV, refs 1. 2) has been found to be strongly associated with CCD (3). Segments of the IAPV genome have been shown to incorporate into the bee genome, and bees carrying integrated IAPV sequences become resistant to IAPV (2). We will discuss the postulated possibility (currently under study) that this integration may cause alteration in the bee behavior, leading to CCD. We will also show that Varroa is infected with IAPV, and the viral sequences are integrated into the Varroa genome. We will discuss the aspect that in addition to IAPV, stress is a factor that turn IAPV-carrying bees (in their genome) to develop CCD. We will also show that IAPV can easily and practically be silenced in bees and discuss the outcome of these experiments. 1. E. Maori, E. Tanne, I. Sela, Virology 362, 342 (2007). 2. E. Maori et al., J. Gen. Virol. 88, 3428 (2007). 3. D. Cox-Foster et al., Science 318, 283 (2007).

Deformed wing virus (DWV) is a viral pathogen of the European honeybee (Apis mellifera) associated with clinical symptoms and colony collapse when transmitted by the ectoparasitic mite Varroa destructor (V. destructor). In the absence of V. destructor DWV-infection does not result in visible symptoms. Analysis of the transmission routes for DWV revealed that DWV is transmitted horizontally within the colony and both, vertically and vectorially between and within colonies. Detailed analysis of horizontal and vertical transmission revealed that these routes did not cause any visible symptoms of disease suggesting that mite-independent transmission results in true covert infections. Overt DWV infections in bees are triggered by the transmission of the virus through the ectoparasitic mite Varroa destructor. Recently, it could be shown that replication of DWV in mites correlated with the occurrence of crippled wings. To further study this phenomenon viral loads were determined in mites. Correlation of these results with the development of clinical symptoms strengthened our hypothesis that replication of DWV in mites prior to transmission is one of the key factors in the pathogenesis of overt 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