Israeli acute paralysis virus (IAPV) is a widespread RNA virus of honey bees that has been linked with colony losses. Here we describe the transmission, prevalence, and genetic traits of this virus, along with host transcriptional responses to infections. Further, we present RNAi-based strategies for limiting an important mechanism used by IAPV to subvert host defenses. Our study shows that IAPV is established as a persistent infection in honey bee populations, likely enabled by both horizontal and vertical transmission pathways. The phenotypic differences in pathology among different strains of IAPV found globally may be due to high levels of standing genetic variation. Microarray profiles of host responses to IAPV infection revealed that mitochondrial function is the most significantly affected biological process, suggesting that viral infection causes significant disturbance in energy-related host processes. The expression of genes involved in immune pathways in adult bees indicates that IAPV infection triggers active immune responses. The evidence that silencing an IAPV-encoded putative suppressor of RNAi reduces IAPV replication suggests a functional assignment for a particular genomic region of IAPV and closely related viruses from the Family Dicistroviridae, and indicates a novel therapeutic strategy for limiting multiple honey bee viruses simultaneously and reducing colony losses due to viral diseases. We believe that the knowledge and insights gained from this study will provide a new platform for continuing studies of the IAPV–host interactions and have positive implications for disease management that will lead to mitigation of escalating honey bee colony losses worldwide.

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The Israeli acute paralysis virus (IAPV) is a significant marker of honeybee colony collapse disorder (CCD). In the present work, we provide the first evidence that Varroa destructor is IAPV replication-competent and capable of vectoring IAPV in honeybees. The honeybees became infected with IAPV after exposure to Varroa mites that carried the virus. The copy number of IAPV in bees was positively correlated with the density of Varroa mites and time period of exposure to Varroa mites. Further, we showed that the mite-virus association could possibly reduce host immunity and therefore promote elevated levels of virus replication. This study defines an active role of Varroa mites in IAPV transmission and sheds light on the epidemiology of IAPV infection in honeybees.Varroatosis is one of the most serious honeybee diseases caused by a parasitic mite, Varroa destructor. Varroa mites use their piercing mouthparts to suck out haemolymph from honeybees. The repeated feeding results in a decline of colony vigour, shortened life span of the honeybees and eventual perishing of colonies (Rosenkranz et al., 2010). Further, the feeding of Varroa mites gives mites the potential to act as vectors of bee diseases, presenting additional threats to bee health. The role of Varroa mite as a vector in the transmission of bee viruses has been well documented (Bowen-Walker et al., 1999;Chen et al., 2004;Shen et al., 2005). However, it has not yet been demonstrated if this mite could act as a vector of Israeli acute paralysis virus (IAPV), a virus that was tightly correlated with honeybee colony collapse disorder (CCD), a malady that has decimated honeybee colonies across the USA (Cox-Foster et al., 2007;vanEngelsdorp et al., 2007) and around the world (Neumann & Carreck, 2010). The present study was undertaken to determine the possible role of Varroa mites in the transmission of IAPV and in the promotion of its replication in honeybees. Moreover, the expression of immune-related gene transcripts, apidaecin and eater that are involved in honeybee humoral and cellular immunity (Ertürk-Hasdemir & Silverman, 2005;Evans et al., 2006;Kocks et al., 2005;Simone et al., 2009) was measured in Varroa-challenged bees. Apidaecin is a proline-rich peptide and one of the most prominent components of the honeybee humoral defence against microbial invasion (Evans et al. 2006). Eater is a member of epidermal growth factor-family protein involved cellular immunity, as it plays an important role in phagocytosis (Ertürk-Hasdemir & Silverman, 2005;Kocks et al., 2005). Two strong bee colonies (i.e. with at least seven frames filled with capped brood and food, and covered with adult bees) and two weak colonies (i.e. with a low-adult bee population and fewer than four frames with a small patch of capped brood) that were determined to be free of IAPV infection by RT-PCR assay were selected for transmission studies. Further, the expression levels of vitellogenin, an indicator of the general health of the colonies (Amdam et al., 2005;Simone et al., 2009), were det...

The decline of many bumblebee species ( Bombus spp.) has been linked to an increased prevalence of pathogens caused by spillover from managed bees. Although poorly understood, RNA viruses are suspected of moving from managed honeybees ( Apis mellifera ) into wild bumblebees through shared floral resources. We examined if RNA viruses spillover from managed honeybees, the extent to which viruses are replicating within bumblebees, and the role of flowers in transmission. Prevalence and active infections of deformed wing virus (DWV) were higher in bumblebees collected near apiaries and when neighboring honeybees had high infection levels. We found no DWV in bumblebees where honeybee foragers and honeybee apiaries were absent. The prevalence of black queen cell virus (BQCV) was also higher in bumblebees collected near apiaries. Furthermore, we detected viruses on 19% of flowers, all of which were collected within apiaries. Our results corroborate the hypothesis that viruses are spilling over from managed honeybees to wild bumblebees and that flowers may be an important route for transmission.

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