Journal of Invertebrate Pathology 147 (2017) 51–59 Contents lists available at ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip Review article Viruses of commercialized insect pollinators Sebastian Gisder a, Elke Genersch a,b,⇑ a b Institute for Bee Research, Department of Molecular Microbiology and Bee Diseases, Friedrich-Engels-Str. 32, 16540 Hohen Neuendorf, Germany Freie Universität Berlin, Fachbereich Veterinärmedizin, Institut für Mikrobiologie und Tierseuchen, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany a r t i c l e i n f o Article history: Received 13 June 2016 Revised 18 July 2016 Accepted 20 July 2016 Available online 3 August 2016 Keywords: Honey bee viruses Honey bee Bumblebee Mason bee Stingless bee a b s t r a c t Managed insect pollinators are indispensable in modern agriculture. They are used worldwide not only in the open field but also in greenhouses to enhance fruit set, seed production, and crop yield. Managed honey bee (Apis mellifera, Apis cerana) colonies provide the majority of commercial pollination although other members of the superfamily Apoidea are also exploited and commercialized as managed pollinators. In the recent past, it became more and more evident that viral diseases play a key role in devastating honey bee colony losses and it was also recognized that many viruses originally thought to be honey bee specific can also be detected in other pollinating insects. However, while research on viruses infecting honey bees started more than 50 years ago and the knowledge on these viruses is growing ever since, little is known on virus diseases of other pollinating bee species. Recent virus surveys suggested that many of the viruses thought to be honey bee specific are actually circulating in the pollinator community and that pollinator management and commercialization of pollinators provide ample opportunity for viral diseases to spread. However, the direction of disease transmission is not always clear and the impact of these viral diseases on the different hosts remains elusive in many cases. With our review we want to provide an up-to-date overview on the viruses detected in different commercialized pollinators in order to encourage research in the field of pollinator virology that goes beyond molecular detection of viruses. A deeper understanding of this field of virology is urgently needed to be able to evaluate the impact of viruses on pollinator health and the role of different pollinators in spreading viral diseases and to be able to decide on appropriate measures to prevent virus-driven pollinator decline. Ó 2016 Elsevier Inc. All rights reserved. Contents 1. 2. 3. 4. 5. 6. 7. 8. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deformed wing virus (DWV) is the most promiscuous honey bee virus . . . . . . Black queen cell virus (BQCV) is wide spread in honey bees of the genus Apis. Acute bee paralysis virus (ABPV) is another multi host virus . . . . . . . . . . . . . . . Sacbrood virus (SBV) has a rather narrow host range . . . . . . . . . . . . . . . . . . . . . Chronic bee paralysis virus (CBPV) and slow bee paralysis virus (SBPV) . . . . . . Newly discovered viruses of unknown relevance . . . . . . . . . . . . . . . . . . . . . . . . Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. Introduction Reproduction and fruit set of plants depend on pollination which can be mediated through water, wind, or animals. The latter ⇑ Corresponding author at: Institute for Bee Research, Department of Molecular Microbiology and Bee Diseases, Friedrich-Engels-Str. 32, 16540 Hohen Neuendorf, Germany. E-mail address: [email protected] (E. Genersch). http://dx.doi.org/10.1016/j.jip.2016.07.010 0022-2011/Ó 2016 Elsevier Inc. All rights reserved. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 52 54 55 55 56 56 56 57 are estimated to contribute to the sexual reproduction of 90% of existent angiosperm species (Aizen et al., 2009; Kearns et al., 1998) which also comprise all the crops directly or indirectly contributing to human nutrition. At least 35% of the global crop production volume comes from crops that depend on animal pollination (Klein et al., 2007) resulting in a global value of animal pollination in agriculture of around €153 billion per year (Gallai et al., 2009). Among the pollinating animals active on flowering plants are bats, birds, and primarily insects like bees, flies, beetles, 52 S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 butterflies, and moths. Recently, an impressive worldwide study on the impact of wild insect pollinators has been conducted for 41 crop systems at 600 different locations and revealed that flower visitations by wild insect pollinators enhanced fruit set in all studied crop systems (Garibaldi et al., 2013). In contrast, honey bees (Apis mellifera), although widely considered an indispensable pollinating insect species, pollinated less effectively and their flower visitations had a positive effect in only 14% of the surveyed crops (Garibaldi et al., 2013). Surprisingly, honey bees did neither maximize pollination nor were they able to fully substitute the lack of wild insects. Therefore, the importance of pollination by wild insects in agricultural ecosystems should not be underestimated. However, in agriculture, managed insect pollinators have an undoubted advantage over wild insect pollinators: They are movable to wherever necessary so that field-grown and greenhousegrown crops alike can be stocked with high densities of the best suited pollinator species. Widely used as commercial pollinators are different social and solitary bee species belonging to the family Apidae. The polylectic honey bees (Apis mellifera, Apis cerana) are generalist pollinators managed by humans since several thousands of years, mostly for honey production. Nowadays, honey bees are used for commercial pollination of crops in the open field worldwide. Actually, A. mellifera is the dominantly used honey bee species and the demand for honey bee pollination is increasing due to the increase in the area cultivated with pollinator dependent crops (Aizen et al., 2008). Accordingly, data from the Food and Agriculture Organization of the United Nations (FAO; http://faostat3.fao.org/home/E) confirm a continuous increase in the global number of managed A. mellifera colonies over the last 55 years (Aizen et al., 2008; Aizen and Harder, 2009; Moritz and Erler, 2016; vanEngelsdorp and Meixner, 2010). In Central and South America, the eusocial Melipona bees, which are a genus of stingless bees, play an important role in honey production. They are the dominant insect pollinators in the open field in the neotropic ecozone (Sommeijer, 1999). In greenhouses, managed bumblebees (Bombus spp.) are the preferred pollinators worldwide. Their commercial production started in 1987 and it is an ever growing business due to the still increasing demand for pollination of various crops cultivated in greenhouses (Velthuis and van Doorn, 2006; Zhang et al., 2015). The alfalfa leafcutting bee (Megachile rotundata) is the most intensively managed solitary bee and used for commercial pollination in e.g., alfalfa or blueberry fields (Pitts-Singer and Cane, 2011). Different species of the solitary mason bee (Osmia spp.) are being developed as manageable alternative crop pollinators especially for orchards (Bosch and Kemp, 2002; Sedivy and Dorn, 2014). In the recent past, devastating losses of managed honey bee colonies (Apis mellifera, Apis cerana) have been reported from all parts of the world. Due to the indispensable role of honey bees for commercial crop pollination these losses caused and still cause great concern among bee keepers, farmers and scientists alike because they might pose a serious threat to human food production. Although these losses are a complex phenomenon, there is a general consensus that both parasitic mites (Varroa destructor, Acarapis woodi, Tropilaelaps spp.) and honey bee viruses play an important role (Anderson and Roberts, 2013; Bacandritsos et al., 2010; Baker and Schroeder, 2008; Berenyi et al., 2006; Cox-Foster et al., 2007; Forsgren et al., 2009; Gauthier et al., 2007; Genersch et al., 2010; Kojima et al., 2011; Li et al., 2012, 2014; Meixner et al., 2014; Nielsen et al., 2008; Runckel et al., 2011; Soroker et al., 2011; Tentcheva et al., 2004; vanEngelsdorp et al., 2009). Recently, managed Melipona scutellaris colonies in Brazil have experienced dramatic losses which were reported to be linked to virus infections (Ueira-Vieira et al., 2015). Alarming declines in bumble bee populations have also been reported and related to the microsporidian pathogen Nosema bombi (Cameron et al., 2011), reduced genetic diversity (Cameron et al., 2011), climatic factors (Kerr et al., 2015), and virus infections putatively spilled over from managed honey bee colonies (Fürst et al., 2014). Hence, virus infections are often implicated in losses of managed bee species. It has recently been shown that RNA viruses are widespread in hymenopteran pollinators and transmitted not only between hymenopteran taxa (Ravoet et al., 2014; Singh et al., 2010) but also to non-hymenopteran arthropods associated with honey bee apiaries (Levitt et al., 2013). Therefore, viruses which were originally thought to be honey bee specific are much more widespread and transmission of RNA viruses between managed bees and wild bees is a common phenomenon (McMahon et al., 2015) although the directionality of virus transmission remains elusive in most cases (Tehel et al., 2016). It is, therefore, not surprising that honey bee viruses are frequently found in flower visiting insects (Mazzei et al., 2014) and especially insect pollinators and that the host range of honey bee viruses will increase with an increasing number of studies on non-Apis pollinators. The geographic range of managed Apis mellifera colonies is nearly worldwide as is the range of the accompanying honey bee viruses. Until now, more than 20 viruses have been detected in honey bees and most of them are positive- and single-stranded RNA viruses of the families Dicistroviridae and Iflaviridae (Chen and Siede, 2007; Li et al., 2014; Runckel et al., 2011). These viruses might form so-called mutant clouds existing as variant swarms or clades rather than as a species defined by a consensus sequence (Domingo and Holland, 1997; Lauring and Andino, 2010). This quasispecies nature of RNA viruses has to be taken into account when evaluating bee virus detection studies performed via PCR-based methods: primers designed for a specific virus will always only detect those viruses of the mutant cloud whose genome sequences are not (yet) mutated in the region of the primer binding sites. Viruses belonging to the same quasispecies but carrying a mutation in one or both of the primer binding sites will remain undetected even if they actually represent the majority of the mutant cloud present in the specific host. Hence, commonly used RT-PCR protocols for the species-specific detection of most of the honey bee viruses are prone to produce false negative results. Therefore, the distribution of viruses, which were originally thought to be honey bee specific, in different taxa might be heavily underestimated. In the following part of our review we will focus on virus infections in the above mentioned managed pollinator bee species. We are aware that our selection of bee species represents only a fraction of the relevant species of insect pollinators. However, the number of studies on pathogen occurrence, infectivity and virulence relates to the importance of the insect species. Therefore, little or close to nothing is known about viruses in non-managed bee species. Most data are available on viruses in Apis species; Bombus species are also covered quite well; few data exist for not dominantly managed species like Melipona and Osmia. For these species, mostly PCR detection of viruses is reported but pathogenicity or virulence of detected viruses for the putative host species remains elusive. No viruses have been reported for Megachile so far (Table 1). 2. Deformed wing virus (DWV) is the most promiscuous honey bee virus For DWV (Iflaviridae), one of the most abundant honey bee viruses, it is already accepted that it exists as a quasispecies (Martin et al., 2012; Mordecai et al., 2016) and forms the DWV/ VDV-1 (deformed wing virus/Varroa destructor virus-1) clade (de Miranda and Genersch, 2010). Virulence of representatives of S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 53 Table 1 Detection and proof of infection or replication of honey bee viruses in managed and wild pollinator insects. (See below-mentioned references for further information.) Note: (+), molecular detection of viral genomes; (++), proof of viral replication; ( ), not yet detected; (Ø), not yet analyzed; DWV, deformed wing virus; VDV-1, Varroa destructor virus-1; ABPV, acute bee paralysis virus; SBV, sacbrood virus: CSBV, Chinese sacbrood virus: IAPV, Israeli acute paralysis virus; CBPV, chronic bee paralysis virus; KBV, Kashmir bee virus; SBPV, slow bee paralysis virus; LSV, Lake Sinai virus strain 1 and strain 2; AmFV: Apis mellifera filamentous virus; ALPV, aphid lethal paralysis virus; BSRV, Big Sioux River virus; BeeMLV, Bee Macula-like virus; A. mellifera, Apis mellifera; A. cerana, Apis cerana, B. agrorum, Bombus agrorum; B. atratus, Bombus atratus; B. hortorum, Bombus hortorum; B. huntii, Bombus huntii; B. ignitus, Bombus ignitus; B. impatiens, Bombus impatiens; B. lapidarius, Bombus lapidarius; B. lucorum, Bombus lucorum; B. pascuorum, Bombus pascuorum; B. pratorum, Bombus pratorum; B. ruderarius, Bombus ruderarius; B. ternarius, Bombus ternarius; B. terrestris: Bombus terrestris, B. vagans, Bombus vagans; M. scutellaris, Melipona scutellaris; O. cornuta, Osmia cornuta; O. bicornis, Osmia bicornis; managed and commercialized species are highlighted by an asterisk. the DWV-clade to both honey bee individuaĺs and colonies is clearly depending on the ectoparasitic mite Varroa destructor acting as biological vector of DWV (Gisder et al., 2009; Möckel et al., 2011; Schöning et al., 2012; Yue and Genersch, 2005) and it has even been proposed that DWV and V. destructor are ‘‘linked in a mutualistic symbiosis” (Di Prisco et al., 2016). Moreover, it has been proposed that V. destructor not only influences the diversity of the DWV-clade within honey bee colonies (Mordecai et al., 2016) but also at the population level (Martin et al., 2012). However, despite this intricate relationship between DWV and the mite, DWV has not been introduced into the honey bee population by the mite but also existed and still exists in bee populations that never had any or still have no contact with the mite (Mondet et al., 2014; Shutler et al., 2014; Singh et al., 2010; Wilfert et al., 2016; Yue and Genersch, 2005). In the absence of V. destructor, DWV transmission occurs vertically via eggs and drone sperm and horizontally via larval food, trophallaxis, or cannibalism of miteparasitized, heavily DWV-infected pupae by adult bees engaged in hygienic behavior (Ravoet et al., 2015b; Schöning et al., 2012; Yue et al., 2007). These transmission routes result in covert infections, hence, in infected animals not exhibiting any symptoms (Hails et al., 2008; Möckel et al., 2011). In contrast, overt DWV infections are dependent on the mite acting as biological DWV vector while parasitizing pupae. Overt infections most often result in pupal death, the development of non-viable adult bees with malformed appendages or adult bees emerging as healthy looking individuals but suffering from an infection of the brain and nervous system, as recently reviewed by (de Miranda and Genersch, 2010; McMenamin and Genersch, 2015). The triangular relationship between honey bees, DWV, and Varroa mites is very complex and most aspects of it still remain elusive. Over the past decade, many studies, some of them being contradictory, have been published trying to understand this relationship at individual host, cellular, and molecular level. For instance, it had been demonstrated that mite infestation induces an immunosuppression in the parasitized honey bee pupa which in turn activates DWV replication (Yang and Cox-Foster, 2005). Hence, DWV would be dependent on the mite’s immunosuppressive activity for full reproductive capacity in pupae. However, other studies did not support a general immunosuppressive effect of mite infestation but rather showed that with increasing numbers of mites per pupa the immune response may also be activated (Gregory et al., 2005; Navajas et al., 2008; Zhang et al., 2010). Unfortunately, the impact of an increased immune response upon mite infestation on DWV replication and virulence in pupae was not analyzed in these studies. Most recently, it was suggested that DWV induces immunosuppression in infected pupae and in turn promotes mite reproduction (Di Prisco et al., 2016). In this scenario, the mite would be dependent on DWV’s immunosuppressive activity for full reproductive capacity. To fully understand and verify this proposed ‘‘loop of reciprocal stimulation of the two symbionts” (Di Prisco et al., 2016), much more research is needed. However, this example might already show that reviewing and evaluating all the data available on the interaction between honey bees, DWV, and varroa mites goes beyond the scope of this review and rather deserves a review of its own. 54 S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 Within the scope of this review, however, is the multi host character of DWV and its infectivity for other pollinating insects. DWV is not only the most prevalent virus in the A. mellifera populations worldwide, but it also has the broadest host range among the viruses originally thought to be specific for A. mellifera (Table 1). In Asian countries, DWV is prevalent in A. cerana colonies irrespectively whether they are managed, non-managed, isolated without any prior contact to A. mellifera or feral colonies (Ai et al., 2012; Forsgren et al., 2015; Wang et al., 2015; Zhang et al., 2012). DWV could also be detected in the non-managed honey bee species A. dorsata and A. florea (Zhang et al., 2012). So far, there are no reports on clinical symptoms (e.g., crippled wings) associated with DWV infections in these honey bee species. Since DWV infections were not restricted to honey bee species that had been in contact to A. mellifera colonies, a possible spill-over from A. mellifera colonies is an unlikely reason for the presence of DWV in other Apis species. A more likely explanation is that DWV is a multi-host-pathogen which has been considered honey bee specific in the past just for the lack of data on other host species. DWV has also been detected in several species of bumblebees although the prevalence found in the various studies differed considerably. In a case study from Columbia, 19 samples of Bombus atratus worker bees were screened for the presence of several honey bee viruses and DWV was present in 100% of the samples (Gamboa et al., 2015). In contrast, in Bombus impatiens from Mexico, the prevalence of RNA viruses generally was very low and out of 120 samples only three (2.5%) were positive for DWV (SachmanRuiz et al., 2015). In a large scale field study in Pennsylvania (USA), analysis of DWV replication was included and revealed active DWV infections in the bumble bee species B. impatiens and B. vagans (Levitt et al., 2013). Such active infections might even lead to overt or lethal infections in bumblebees as the occurrence of crippled wings in B. terrestris and B. pascuorum could already be related to DWV-infections (Genersch et al., 2006) and experimental infection of B. terrestris resulted in a high mortality (50%) of the infected animals 15 days post infection (Graystock et al., 2016b). Honey bees have been discussed as the source of the described overt bumblebee DWV infections (Genersch et al., 2006). Moreover, DWV spill-over from A. mellifera colonies has been shown to be one, if not the main route of DWV infection for bumblebees in the field (Fürst et al., 2014; McMahon et al., 2015). This finding even culminated in the media statement that honey bees may be the ‘‘Typhoid Marys” for bumblebees and the pollinator world. In the course of a broad study looking for honey bee viruses in solitary bees, DWV could only be detected in Osmia bicornis (Ravoet et al., 2014). However, the host range of DWV is not restricted to members of the superfamily Apoidea because DWV has also been detected in adults of the genus Vespula (superfamily Vespoidea) (Levitt et al., 2013). The question, whether these insects were actually infected or only carried the viruses in their intestine because they consumed contaminated nectar or pollen, could not be answered because total RNA was isolated from whole body extracts and viral replication was not analyzed. The host range of the DWV clade is even not restricted to the class Insecta because its replication in V. destructor mites (Gisder et al., 2009; Ongus et al., 2004; Yue and Genersch, 2005) proves that it can also actively infect members of the class Arachnida. Initially, the identified sequence differences between VDV-1, originally detected as a virus replicating in the mite, and the deposited genome sequences of DWV isolated from honey bees led to the assumption that VDV-1 represents a virus species of its own (Ongus et al., 2004). However, further analyses of VDV-1 infectivity and pathology in honey bees (Zioni et al., 2011) rather suggested that VDV-1 is one of the many variants of the DWV mutant cloud. The DWV mutant cloud had already been shown to contain variants able to replicate in mites and these variants could be related to increased DWV virulence in bees (Gisder et al., 2009; Schöning et al., 2012; Yue and Genersch, 2005). 3. Black queen cell virus (BQCV) is wide spread in honey bees of the genus Apis BQCV belongs to the genus Cripavirus within the family Dicistroviridae (Mayo, 2002a,b). This virus was first described in 1977 when it was isolated from A. mellifera queen pupae and pre-pupae which were found decomposed in patchily black colored cells (Bailey and Woods, 1977). Case studies confirmed BQCV to be the most common cause of death in queen larvae (Anderson, 1993; Benjeddou et al., 2001) and suggested an association between weakening of colonies and BQCV infection (Daughenbaugh et al., 2015). BQCV is now considered one of the most common and prevalent virus infections in A. mellifera worldwide (Antunez et al., 2006; Berenyi et al., 2006; de Graaf et al., 2008; Higes et al., 2007; Hornitzky, 1987; Mookhploy et al., 2015; Singh et al., 2010; Tentcheva et al., 2004; Topolska et al., 1995; Zhang et al., 2012) (Table 1). In China, Thailand, and Japan, BQCV was detected in the native honey bees Apis cerana indica, Apis cerana japonica, Apis dorsata (giant honey bee), and Apis florea (dwarf honey bee) and also in non-native Apis mellifera colonies (Mookhploy et al., 2015; Zhang et al., 2012) (Table 1). Phylogenetic analyses based on the partial capsid protein coding region gave contradictory results in respect to whether isolates cluster according to geography or according to Apis species. BQCV virus isolates from Thailand and Japan revealed a geographical clustering rather than a clustering according to Apis species. In this study, isolates from one geographical region derived from different Apis species were more closely related than isolates from one Apis species originating from different regions (Mookhploy et al., 2015). These results are in accordance with another phylogenetic study from Japan which showed close genetic relationship of BQCV isolates from A. mellifera and A. cerana japonica (Kojima et al., 2011). They also support the notion that the partial capsid protein gene sequences of BQCV in A. mellifera are suitable to differentiate virus isolates from different geographic origins (Reddy et al., 2013; Tapaszti et al., 2009) and extends this finding to other Apis species. The studies in Japan and Thailand suggest that transmission of BQCV between different Apis species is determined by sharing the same habitat and visiting the same flowers and include the possibility of virus spillover from managed A. mellifera colonies to native bee species. However, a phylogenetic tree from China showed clustering according to honey bee species (A. mellifera, A. florea, A. dorsata) rather than according to region (Zhang et al., 2007) suggesting virus adaptation to different hosts. Unfortunately, in the latter study the genomic region used for phylogeny is not clearly given making it impossible to fully evaluate this study and its impact. The host range of BQCV is not restricted to Apis species but also includes Bombus species (Table 1). In the course of several field surveys, BQCV genomic RNA was detected by molecular methods in different Bombus species (Choi et al., 2015, 2010; Gamboa et al., 2015; McMahon et al., 2015; Reynaldi et al., 2013; Singh et al., 2010) (Table 1). While in these field studies only presence of viral RNA but no viral replication was analyzed, another experimental study detected BQCV in different tissues of bumblebees (B. huntii) caught in the wild or reared in the lab and showed that viral replication was restricted to the gut (Peng et al., 2011). Surprisingly, BQCV infections were more widespread in the body of fieldcollected bumblebees than in the body of lab-reared individuals suggesting that the virus is rather taken up during the natural foraging activity of bumblebees and less so during the mass rearing process (Peng et al., 2011). These findings and the fact that BQCV from US populations of bumblebees and honey bees were S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 phylogenetically closely related (Peng et al., 2011) argue for an oral infection route via virus contaminated food. A prerequisite for this would be that BQCV is circulating in an ecosystem inhabited by both honey bees and bumblebees. Infected honey bee colonies may be the source of BQCV contaminating shared nectar and pollen resources (McMahon et al., 2015). 4. Acute bee paralysis virus (ABPV) is another multi host virus ABPV (Dicistroviridae) is a member of a complex of three closely related viruses comprising also Kashmir bee virus (KBV) and Israeli acute paralysis virus (IAPV), which is, hence, named AKI-complex (de Miranda et al., 2010a). Phylogenetic analyses clearly revealed genomic and evolutionary differences between the sequenced representatives of these three viruses (de Miranda et al., 2010a, 2004; Maori et al., 2007). However, considering that ABPV, KBV, and IAPV are single- and plus-stranded RNA viruses which exist as quasispecies and form mutant clouds, it still remains to be determined whether these three viruses really represent separate species or are just distant variants of the same mutant cloud. All three viruses have in common that they are highly virulent and lethal within a couple of days when injected into pupae or adult A. mellifera bees (Bailey et al., 1963; Maori et al., 2007). ABPV has been detected in V. destructor parasitizing A. mellifera colonies (Bakonyi et al., 2002) and there is statistical evidence that ABPV infections contribute to colony losses (Bakonyi et al., 2002; Berenyi et al., 2006; Berthoud et al., 2010; Francis et al., 2013; Genersch et al., 2010; Nordstrom et al., 1999). So far, it has not been shown that ABPV can replicate in V. destructor. It has been suggested that the high virulence of ABPV towards honey bees prevented this virus to develop an intricate association with V. destructor in a similar manner as DWV did because ABPV transmitted by V. destructor to pupae results in pupal death. Hence, this association is a dead end road for both, virus and mite (de Miranda et al., 2010a). While ABPV or, more general, members of the AKI-complex are widespread not only in weak or collapsing (Bakonyi et al., 2002; Berenyi et al., 2006; Genersch et al., 2010) but also in healthy A. mellifera colonies (Tentcheva et al., 2004), these viruses are rather rarely found in Apis cerana colonies (Forsgren et al., 2015) (Table 1). In Asia, increased infections rates were detected in managed A. cerana colonies and in A. cerana colonies in the vicinity of managed A. mellifera colonies suggesting a spillover effect from the non-native A. mellifera to the native A. cerana bees (Forsgren et al., 2015). Shortly after its discovery it became evident that the host range of ABPV goes beyond A. mellifera because it was also detected as causing inapparent infections in bumblebees from the field (Table 1). Recent studies confirmed these findings of ABPV infections in field samples of Bombus spp. (Bailey and Gibbs, 1964; Gamboa et al., 2015; Sachman-Ruiz et al., 2015; Singh et al., 2010) and even demonstrated that ABPV was significantly more prevalent in bumblebee than honey bee foragers (McMahon et al., 2015). Therefore, ABPV infections in bumblebees may not represent a recent phenomenon or classify as emerging infectious disease (EID) in bumblebees and honey bee colonies may not necessarily be the source of infection. The other members of the AKI-complex, KBV and IAPV, could also be detected in bumblebees (Sachman-Ruiz et al., 2015; Singh et al., 2010) and there is evidence for IAPV that the infection is spreading from infected honey bee colonies into non-Apis hymenopteran pollinators (Singh et al., 2010). Infection experiments conducted with several Bombus species revealed that adults of all tested species were susceptible towards injection of virus particles and developed symptoms of fatal paralysis (Bailey and Gibbs, 1964). Recent experimental studies revealed 55 that also IAPV is highly virulent for B. terrestris when injected into adult bumblebees: Injection of as little as 20 viral particles caused 100% mortality within six days (Niu et al., 2016). In contrast, oral infection of B. terrestris workers with KBV or IAPV did not result in increased mortality. However, micro-colonies established by infected workers exhibited significantly delayed oviposition by the pseudo-queen (only KBV) and reduced drone production (KBV and IAPV) (Meeus et al., 2014). Oral transmission is the most likely natural infection route for bumblebees with members of the AKI-complex. Therefore, immediate symptoms like increased worker mortality only seen after virus injection are less likely in the field than sublethal effects on the reproductive success of bumblebee colonies. Further studies are needed to evaluate the overall impact of these virus infections for bumblebees. The host range of ABPV/KBV/IAPV might not be restricted to Apis and Bombus species: a molecular screening of bees from M. scutellaris colonies in Brazil for seven common honey bee viruses revealed that from the AKI-complex only ABPV was present and could be found in 100% of the sampled colonies (Table 1) (Ueira-Vieira et al., 2015). Again, A. mellifera has been discussed as possible source of infection because pollen and honey produced by A. mellifera colonies and presumably contaminated with viral particles are used in meliponiculture as a supplemental food source (Ueira-Vieira et al., 2015). ABPV genome detection statistically correlated with the occurrence of dead stingless bees in the surveyed meliponary thus suggesting that ABPV infections might be involved in the observed decrease in the stingless bee population and increase in the number of dead stingless bees in individual colonies (Ueira-Vieira et al., 2015). However, ABPV replication in Melipona bees was not analyzed and, therefore, further studies are necessary to determine ABPV pathogenicity and virulence for stingless bees. 5. Sacbrood virus (SBV) has a rather narrow host range SBV (family Iflaviridae) is one of the most common viruses in A. mellifera and A. cerana (Table 1 and references therein) and the etiological agent of the brood disease sacbrood. SBV is transmitted to larvae by covertly infected nurse bees (Bailey, 1969). Following infection by virus contaminated larval food, the larvae fail to pupate (Bailey et al., 1964; Chen and Siede, 2007) and acquire a sac-like appearance which can be readily diagnosed in the field. Although sacbrood disease is lethal for infected larvae, colonies showing symptoms of sacbrood rarely collapse and, hence, SBV poses a moderate threat to managed honey bees. Several strains of SBV have been isolated worldwide. Recently described strains are Korea sacbrood virus, KSBV (Reddy et al., 2016), Chinese sacbrood virus, CSBV (Zhang et al., 2013) and Thai sacbrood virus, TSBV (Rana et al., 2011). Phylogenetic analysis revealed the existence of an European serotype, a New Guinea serotype, and an Asian serotype as well as several subtypes within each serotype (Roberts and Anderson, 2014). Although SBV has also been detected in V. destructor (Mondet et al., 2014; Shen et al., 2005), no replication of SBV in V. destructor has been demonstrated so far suggesting that the mite does neither serve as host nor as biological vector for SBV. Instead, the mite might serve as mechanical SBV vector after acquiring virus particles through parasitizing SBV infected pupae or adult bees (Shen et al., 2005). In honey bee colonies parasitized by V. destructor, viral infections by DWV, KBV, and SBV had a significant higher prevalence compared to honey bee colonies which were free of mites suggesting a vectorial transmission of SBV (Mondet et al., 2014). Only few reports on SBV detection in non-Apis-bees exist despite the fact that nearly all studies on virus detection in insect pollinators included SBV. This indicates a rather narrow host range 56 S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 for SBV (Table 1). SBV viral RNA could be detected in several Bombus species (Gamboa et al., 2015; McMahon et al., 2015; Reynaldi et al., 2013; Singh et al., 2010) and in the solitary bee Andrena vaga (Ravoet et al., 2014) (Table 1). Pathogenicity and virulence of SBV for these putative hosts cannot be finally evaluated because neither viral replication nor symptoms of sacbrood disease were analyzed in these studies. 6. Chronic bee paralysis virus (CBPV) and slow bee paralysis virus (SBPV) CBPV is an unclassified virus phylogenetically placed between the Nodaviridae family of insect and fish viruses and the plant virus family Tombusviridae (Ribiere et al., 2010, 2002). CBPV is a rather unusual honey bee virus in that it is an enveloped virus with a genome consisting of two single-, plus-stranded RNA molecules. CBPV was first isolated in 1963 from diseased bees showing symptoms of paralysis like incapacity to fly, ataxia, and trembling (Bailey et al., 1963). CBPV shows neurotropism in Apis mellifera (Olivier et al., 2008) explaining the neurological symptoms in infected bees. CBPV is worldwide distributed in Apis mellifera populations (Ribiere et al., 2010) but was also found in Apis cerana (Wang et al., 2015), in Bombus terrestris (Choi et al., 2010), and Bombus impatiens (Sachman-Ruiz et al., 2015). In addition, CBPV is able to infect ants (Formica rufa, Camponotus vagus) and V. destructor (Celle et al., 2008) and it has been discussed that ants represent a virus reservoir and the mite serves as virus vector facilitating CBPV spreading in the honey bee population. SBPV belongs to the virus family Iflaviridae (de Miranda et al., 2010b) and has been described as etiological agent of a rather slow form of paralysis of adult bees: upon injection of SBPV, adult bees died within approximately 12 days and showed paralysis of the anterior two pairs of legs one or two days before death (Bailey and Woods, 1974). Using serological detection methods, SBPV was implicated in V. destructor induced colony losses (Carreck et al., 2010). Molecular detection of SBPV became feasible only recently with the publication of the genomic sequence of SBPV (de Miranda et al., 2010b). Hence, many virus surveys in honey bee populations do not include analysis of SBPV. However, analyzing samples from different European countries for SBPV using newly developed RT-PCR protocols revealed a low natural prevalence of SBPV in the European honey bee population (de Miranda et al., 2010b). A recent virus detection study in wild bumblebees collected in the UK (McMahon et al., 2015) and in Belgium (Parmentier et al., 2016) revealed that SBPV infections can also occur in bumblebees albeit with a low prevalence. Despite the low detection rate, SBPV was slightly more prevalent in bumblebees than in honey bees (McMahon et al., 2015) questioning the direction of SBPV transmission between managed and wild pollinators (Parmentier et al., 2016). 7. Newly discovered viruses of unknown relevance Reports on devastating honey bee colony losses and on declines in bumblebee populations caused an increased scientific interest in the pathogens, including viruses, presumably involved in these phenomena. In order to detect more than the known and usually taken seven to eight honey bee viruses, next generation sequencing methods were recently introduced for bee virus detection studies. In a case study, 20 migratory honey bee colonies were analyzed for the common seven honey bee viruses (CBPV, IAPV, DWV, ABPV, BQCV, SBV, KBV) using the Arthropod Pathogen Microarray (APM) which is capable of detecting over 200 arthropod associated viruses, microbes, and metazoan parasites. In addition, an ultra- deep sequencing approach was applied and led to the discovery of four distinct viruses which were either novel (Lake Sinai virus strain 1 and strain 2 (LSV1 and 2; presumably Noraviridae) and Big Sioux River virus (BSRV; Dicistroviridae)) or had not been associated with honey bees so far (aphid lethal paralysis virus (ALPV; Dicistroviridae)), (Runckel et al., 2011) (Table 1). ALPV and BSRV could be detected in almost every sample during the 10 month sampling period. ALPV and LSV were shown to replicate in honey bees (Ravoet et al., 2015a, 2013; Runckel et al., 2011) and prevalence of LSV-1 and LSV-2 was further investigated in six colonies which were monitored over a three month period. The results from this small sample cohort suggested an association between weakening of colonies and infections with LSV1, LSV2, and BQCV (Daughenbaugh et al., 2015). However, there was no statistically significant evidence that LSV strains contribute to colony mortality (Daughenbaugh et al., 2015). In the meantime, a number of additional LSV strains has been described (Cornman et al., 2012; Granberg et al., 2013; Ravoet et al., 2015a, 2013) underlining the major strain diversity that appears to exist and co-circulate for many RNA-bee viruses. LSV was also detected in mason bees although viral replication could only be demonstrated in Osmia cornuta but not in Osmia bicornis (Ravoet et al., 2015a). In V. destructor, only the positive sense LSV genome could be detected but not the negative-strand intermediate only occurring during viral replication suggesting the absence of replicating virus (Ravoet et al., 2015a). Hence, V. destructor might serve as mechanical vector in honey bees but is not an alternative host for LSV. Oral transmission routes for LSV through contaminated pollen seem likely considering that LSV was found in pollen pellets (Ravoet et al., 2015a). In addition, the known Apis mellifera filamentous virus (AmFV; an unclassified DNA virus) (Clark, 1978; Gauthier et al., 2015) and a novel virus now called Bee macula-like virus (BeeMLV, Tymoviridae) (de Miranda et al., 2015) were recently discovered in honey bees (Ravoet et al., 2013) and subsequently also detected in bumblebees and mason bees (Ravoet et al., 2014) (Table 1). While the well-known honey bee viruses are fairly well characterized and experimental studies on their pathogenicity and virulence at least in honey bees have been performed, it still remains elusive whether the viruses recently discovered in managed and wild bees induce individual (or colony) mortality or at least affect the fitness of the infected bee species. Much more research is necessary to fully understand the impact of viral pathogens on the pollinator community. 8. Outlook There is an ever increasing demand in the agricultural sector not only for honey bees but also for alternative non-honey bee pollinators which can be used as managed commercial pollinators under special circumstances (e.g., in greenhouses) or for specific crops (e.g., blueberry, alfalfa). However, mass rearing and commercialization of these insect species is not without problems. Mass rearing of any organism poses the risk of increased disease transmission followed by a higher prevalence of pathogens in the mass reared individuals compared to feral individuals (Colla et al., 2006; Eilenberg et al., 2015). Outbreaks of epidemics not observed in the wild may occur in lab reared or mass reared populations resulting in the collapse – or near collapse – of these populations (Eilenberg et al., 2015). Therefore, special care must be taken to prevent disease transmission and outbreaks in insect production facilities. In the era of globalization, commercialization of pollinators led to their worldwide trade and their importation into countries far beyond their natural geographic range. This already happened to the Western honey bee, A. mellifera, which is native to Europe, Africa and the Middle East (Han et al., 2012) but has been S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 introduced into all regions of the world by beekeeping activities. Likewise, since the commercialization of bumblebees in the late eighties of the 20th century, mainly B. terrestris but also other Bombus species have been imported for greenhouse pollination into many countries where they are not the native bumblebee species. Spillover of diseases from and introduction of new pathogens (emerging infectious diseases, EID) through these non-native pollinators into the native ecosystems might pose a serious threat to these systems and might lead to losses and declines of native wild pollinator species (Goulson, 2003; Goulson and Hughes, 2015; Graystock et al., 2016a). Therefore, a broad knowledge on the pathogens naturally circulating in diverse ecosystems is important to evaluate whether or not pathogens are really newly introduced into a specific host population or are just detected for the first time because they were surveyed for the first time. Likewise, comprehensive knowledge on all pathogens associated with certain pollinators is vital to take appropriate measures in order to prevent that these pathogens become worldwide distributed once their hosts are worldwide distributed (Goulson and Hughes, 2015). References Ai, H.X., Yan, X., Han, R.C., 2012. Occurrence and prevalence of seven bee viruses in Apis mellifera and Apis cerana apiaries in China. J. Invertebr. Pathol. 109, 160– 164. Aizen, M.A., Garibaldi, L.A., Cunningham, S.A., Klein, A.M., 2008. Long-term global trends in crop yield and production reveal no current pollination shortage but increasing pollinator dependency. Curr. Biol. 18, 1572–1575. Aizen, M.A., Garibaldi, L.A., Cunningham, S.A., Klein, A.M., 2009. How much does agriculture depend on pollinators? Lessons from long-term trends in crop production. Ann. Bot. 103, 1579–1588. Aizen, M.A., Harder, L.D., 2009. The global stock of domesticated honey bees is growing slower than agricultural demand for pollination. Curr. Biol. 19, 1–4. Allen, M.F., Ball, B.V., 1995. Characterization and serological relationships of strains of Kashmir bee virus. Ann. Appl. Biol. 126, 471–484. Anderson, D.L., 1993. Pathogens and queen bees. Australasian Beekeeper 94, 292– 296. Anderson, D.L., Roberts, J.M.K., 2013. Standard methods for Tropilaelaps mites research. J. Apicultural Res. 52, 1–16. Antunez, K., D’Alessandro, B., Corbella, E., Ramallo, G., Zunino, P., 2006. Honeybee viruses in Uruguay. J. Invertebr. Pathol. 93, 67–70. Bacandritsos, N., Granato, A., Budge, G., Papanastasiou, I., Roinioti, E., Caldon, M., Falcaro, C., Gallina, A., Mutinelli, F., 2010. Sudden deaths and colony population decline in Greek honey bee colonies. J. Invertebr. Pathol. 105, 335–340. Bailey, L., 1965. Paralysis of the honey bee, Apis mellifera Linnaeus. J. Invertebr. Pathol. 7, 132–140. Bailey, L., 1969. Multiplication and spread of sacbrood virus of bees. Ann. Appl. Biol. 63, 483–491. Bailey, L., Carpenter, J.M., Woods, R.D., 1982. A strain of sacbrood virus from Apiscerana. J. Invertebr. Pathol. 39, 264–265. Bailey, L., Gibbs, A.J., 1964. Acute infections of bees with paralysis virus. J. Insect Pathol. 6, 395–407. Bailey, L., Gibbs, A.J., Woods, R.D., 1963. Two viruses from adult honey bees (Apis mellifera Linnaeus). Virology 21, 390–395. Bailey, L., Gibbs, A.J., Woods, R.D., 1964. Sacbrood virus of the larval honey bee (Apis mellifera Linnaeus). Virology 23, 425–429. Bailey, L., Woods, R.D., 1974. Three previously undescribed viruses from honey bee. J. Gen. Virol. 25, 175–186. Bailey, L., Woods, R.D., 1977. Two more small RNA viruses from honey bees and further observations on sacbrood and acute bee-paralysis viruses. J. Gen. Virol. 37, 175–182. Baker, A., Schroeder, D., 2008. Occurrence and genetic analysis of picorna-like viruses infecting worker bees of Apis mellifera L. populations in Devon, South West England. J. Invertebr. Pathol. 98, 239–242. Bakonyi, T., Farkas, R., Szendroi, A., Dobos-Kovács, M., Rusvai, M., 2002. Detection of acute bee paralysis virus by RT-PCR in honey bee and Varroa destructor field samples: rapid screening of representative Hungarian apiaries. Apidologie 33, 63–74. Benjeddou, M., Leat, N.M.A., Davison, S., 2001. Detection of acute bee paralysis virus and black queen cell virus from honey bees by reverse transcriptase PCR. Appl. Environ. Microbiol. 67, 2384–2387. Berenyi, O., Bakonyi, T., Derakhshifar, I., Koglberger, H., Nowotny, N., 2006. Occurrence of six honey bee viruses in diseased Austrian apiaries. Appl. Environ. Microbiol. 72, 2414–2420. Berthoud, H., Imdorf, A., Haueter, M., Radloff, S., Neumann, P., 2010. Virus infections and winter losses of honey bee colonies (Apis mellifera). J. Apicultural Res. 49, 60–65. 57 Bosch, J., Kemp, W.P., 2002. Developing and establishing bee species as crop pollinators: the example of Osmia spp. (Hymenoptera: Megachilidae) and fruit trees. Bull. Entomol. Res. 92, 3–16. Bowen-Walker, P.L., Martin, S.J., Gunn, A., 1999. The transmission of deformed wing virus between honey bees (Apis mellifera L.) by the ectoparasitic mite Varroa jacobsoni Oud. J. Invertebr. Pathol. 73, 101–106. Cameron, S.A., Loziera, J.D., Strange, J.P., Koch, J.B., Cordes, N., Solter, L.F., Griswold, T.L., 2011. Patterns of widespread decline in North American bumblebees. Proc. Natl. Acad. Sci. USA 108, 662–667. Carreck, N.L., Ball, B.V., Martin, S.J., 2010. Honey bee colony collapse and changes in viral prevalence associated with Varroa destructor. J. Apicultural Res. 49, 93–94. Celle, O., Blanchard, P., Olivier, V., Schurr, F., Cougoule, N., Faucon, J.-P., Ribiere, M., 2008. Detection of chronic bee paralysis virus (CBPV) genome and its replicative RNA form in various hosts and possible ways of spread. Virus Res. 133, 280– 284. Chen, Y.P., Siede, R., 2007. Honey bee viruses. Adv Virus Res 70, 33–80. Chen, Y.P., Smith, I.B., Collins, A.M., Pettis, J.S., Feldlaufer, M.F., 2004. Detection of deformed wing virus infection in honey bees, Apis mellifera L., in the United States. Am. Bee J. 144, 557–559. Choi, N.R., Jung, C., Lee, D.W., 2015. Optimization of detection of black queen cell virus from Bombus terrestris via real-time PCR. J. Asia Pac. Entomol. 18, 9–12. Choi, Y.S., Lee, M.Y., Hong, I.P., Kim, N.S., Kim, H.K., Byeon, K.H., Yoon, H., 2010. Detection of honey bee virus from bumblebee (Bombus terrestris and Bombus ignitus). Korean J. Apiculture 25, 259–266. Clark, T.B., 1978. A filamentous virus of the honey bee. J. Invertebr. Pathol. 32, 332– 340. Colla, S.R., Otterstatter, M.C., Gegear, R.J., Thomson, J.D., 2006. Plight of the bumblebee: pathogen spillover from commercial to wild populations. Biol. Conserv. 129, 461–467. Cornman, R.S., Tarpy, D.R., Chen, Y.P., Jeffreys, L., Lopez, D., Pettis, J.S., vanEngelsdorp, D., Evans, D., 2012. Pathogen webs in collapsing honey bee colonies. PLoS One 7, e43562. Cox-Foster, D.L., Conlan, S., Holmes, E.C., Palacios, G., Evans, J.D., Moran, N.A., Quan, P.-L., Briese, T., Hornig, M., Geiser, D.M., Martinson, V., vanEngelsdorp, D., Kalkstein, A.L., Drysdale, A., Hui, J., Zhai, J., Cui, L., Hutchison, S.K., Simons, J.F., Egholm, M., Pettis, J.S., Lipkin, W.I., 2007. A metagenomic survey of microbes in honey bee colony collapse disorder. Science 318, 283–287. Daughenbaugh, K.F., Martin, M., Brutscher, L.M., Cavigli, I., Garcia, E., Lavin, M., Flenniken, M.L., 2015. Honey bee infecting Lake Sinai viruses. Viruses-Basel 7, 3285–3309. de Graaf, D.C., Brunain, M., Imberechts, H., Jacobs, F.J., 2008. First molecular confirmation of deformed wing virus infections of honey bees from a Belgian apiary reveals the presence of black queen cell virus and Varroa destructor virus 1. Vlaams Diergeneeskundig Tijdschrift 77, 101–105. de Miranda, J., Cordoni, G., Budge, G., 2010a. The acute bee paralysis virus - Kashmir bee virus - Israeli acute paralysis virus complex. J. Invertebr. Pathol. 103, S30– S47. de Miranda, J., Drebot, M., Tyler, S., Shen, M., Cameron, C.E., Stoltz, D.B., Camazine, S. M., 2004. Complete nucleotide sequence of Kashmir bee virus and comparison with acute bee paralysis virus. J. Gen. Virol. 85, 2263–2270. de Miranda, J., Genersch, E., 2010. Deformed wing virus. J. Invertebr. Pathol. 103, S48–S61. de Miranda, J.R., Cornman, R.S., Evans, J.D., Semberg, E., Haddad, N., Neumann, P., Gauthier, L., 2015. Genome characterization, prevalence and distribution of a macula-like virus from Apis mellifera and Varroa destructor. Viruses-Basel 7, 3586–3602. de Miranda, J.R., Dainat, B., Locke, B., Cordoni, G., Berthoud, H., Gauthier, L., Neumann, P., Budge, G.E., Ball, B.V., Stoltz, D.B., 2010b. Genetic characterization of slow bee paralysis virus of the honey bee (Apis mellifera L.). J. Gen. Virol. 91, 2524–2530. Di Prisco, G., Annoscia, D., Margiotta, M., Ferrara, R., Varricchio, P., Zanni, V., Caprio, E., Nazzi, F., Pennacchio, F., 2016. A mutualistic symbiosis between a parasitic mite and a pathogenic virus undermines honey bee immunity and health. Proc. Natl. Acad. Sci. USA 113, 3203–3208. Domingo, E., Holland, J.J., 1997. RNA virus mutations and fitness for survival. Annu. Rev. Microbiol. 51, 151–178. Eilenberg, J., Vlak, J.M., Nielsen-LeRoux, C., Cappellozza, S., Jensen, A.B., 2015. Diseases in insects produced for food and feed. J. Insects Food Feed 1, 87–102. Forsgren, E., de Miranda, J.R., Isaksson, M., Wei, S., Fries, I., 2009. Deformed wing virus associated with Tropilaelaps mercedesae infesting European honey bees (Apis mellifera). Exp. Appl. Acarol. 47, 87–97. Forsgren, E., Shi, W., Ding, G.L., Liu, Z.G., Tran, T.V., Tang, P.T., Truong, T.A., Dinh, T.Q., Fries, I., 2015. Preliminary observations on possible pathogen spill-over from Apis mellifera to Apis cerana. Apidologie 46, 265–275. Francis, R.M., Nielsen, S.L., Kryger, P., 2013. Varroa-virus interaction in collapsing honey bee colonies. PLoS One 8, e57540. Fürst, M.A., McMahon, D.P., Osborne, J.L., Paxton, R.J., Brown, M.F., 2014. Disease associations between honey bees and bumblebees as a threat to the wild pollinators. Nature 506, 364–366. Gallai, N., Salles, J.-M., Settele, J., Vaissière, B.E., 2009. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecol. Econ. 68, 810–821. Gamboa, V., Ravoet, J., Brunain, M., Smagghe, G., Meeus, I., Figueroa, J., Riano, D., de Graaf, D.C., 2015. Bee pathogens found in Bombus atratus from Colombia: a case study. J. Invertebr. Pathol. 129, 36–39. 58 S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 Garibaldi, L.A., Steffan-Dewenter, I., Winfree, R., Aizen, M.A., Bommarco, R., Cunningham, S.A., Kremen, C., Carvalheiro, L.G., Harder, L.D., Afik, O., Bartomeus, I., Benjamin, F., Boreux, V., Cariveau, D., Chacoff, N.P., Dudenhöffer, J.H., Freitas, B.M., Ghazoul, J., Greenleaf, S., Hipólito, J., Holzschuh, A., Howlett, B., Isaacs, R., Javorek, S.K., Kennedy, C.M., Krewenka, K., Krishnan, S., Mandelik, Y., Mayfield, M.M., Motzke, I., Munyuli, T., Nault, B.A., Otieno, M., Petersen, J., Pisanty, G., Potts, S.G., Rader, R., Ricketts, T.H., Rundlöf, M., Seymour, C.L., Schüepp, C., Szentgyörgyi, H., Taki, H., Tscharntke, T., Vergara, C.H., Viana, B.F., Wanger, T.C., Westphal, C., Williams, N., Klein, A.M., 2013. Wild pollinators enhance fruit set of crops regardless of honey bee abundance. Science 339, 1608–1611. Gauthier, L., Tentcheva, D., Tournaire, M., Dainat, B., Cousserans, F., Colin, M.E., Bergoin, M., 2007. Viral load estimation in asymptomatic honey bee colonies using the quantitative RT-PCR technique. Apidologie 38, 426–435. Gauthier, L., Ravallec, M., Tournaire, M., Cousserans, F., Bergoin, M., Dainat, B., de Miranda, J.R., 2011. Viruses associated with ovarian degeneration in Apis mellifera L. queens. PLoS One 6, e16217. Gauthier, L., Cornman, S., Hartmann, U., Cousserans, F., Evans, J.D., de Miranda, J.R., Neumann, P., 2015. The Apis mellifera filamentous virus genome. Viruses 7, 3798–3815. Genersch, E., Ohe, W., Kaatz, H., Schroeder, A., Otten, C., Büchler, R., Berg, S., Ritter, W., Mühlen, W., Gisder, S., Meixner, M., Liebig, G., Rosenkranz, P., 2010. The German bee monitoring project: a long term study to understand periodically high winter losses of honey bee colonies. Apidologie 41, 332–352. Genersch, E., Yue, C., Fries, I., de Miranda, J.R., 2006. Detection of deformed wing virus, a honey bee viral pathogen, in bumble bees (Bombus terrestris and Bombus pascuorum) with wing deformities. J. Invertebr. Pathol. 91, 61–63. Gisder, S., Aumeier, P., Genersch, E., 2009. Deformed wing virus (DWV): viral load and replication in mites (Varroa destructor). J. Gen. Virol. 90, 463–467. Goulson, D., 2003. Effects of introduced bees on native ecosystems. Annu. Rev. Ecol. Evol. Syst. 34, 1–26. Goulson, D., Hughes, W.O.H., 2015. Mitigating the anthropogenic spread of bee parasites to protect wild pollinators. Biol. Conserv. 191, 10–19. Granberg, F., Vicente-Rubiano, M., Rubio-Guerri, C., Karlsson, O.E., Kukielka, D., Belak, S., Sanchez-Vizcaino, J.M., 2013. Metagenomic detection of viral pathogens in Spanish honey bees: co-infection by aphid lethal paralysis, Israel acute paralysis and Lake Sinai viruses. PLoS One 8, e57459. Graystock, P., Blane, E.J., McFrederick, Q.S., Goulson, D., Hughes, W.O.H., 2016a. Do managed bees drive parasite spread and emergence in wild bees? Int. J. Parasitol. Parasites Wildl. 5, 64–75. Graystock, P., Meeus, I., Smagghe, G., Goulson, D., Hughes, W.O.H., 2016b. The effects of single and mixed infections of Apicystis bombi and deformed wing virus in Bombus terrestris. Parasitology 143, 358–365. Gregory, P.G., Evans, J.D., Rinderer, T.E., de Guzman, L., 2005. Conditional immune gene suppression of honeybees parasitized by Varroa mites. J. Insect Sci. 5, 1–5. Hails, R.S., Ball, B.V., Genersch, E., 2008. Infection strategies of insect viruses. In: Aubert, M. et al. (Eds.), Virology and the Honey Bee. European Communities, Luxembourg, pp. 255–275. Han, F., Wallberg, A., Webster, M.T., 2012. From where did the Western honey bee (Apis mellifera) originate? Ecol. Evol. 2, 1949–1957. Higes, M., Esperon, F., Sanchez-Vizcaino, J.M., 2007. Short communication. First report of black queen-cell virus detection in honey bees (Apis mellifera) in Spain. Span. J. Agric. Res. 5, 322–325. Hornitzky, M.A.Z., 1987. Prevalence of virus-infections of honey bees in eastern Australia. J. Apicultural Res. 26, 181–185. Kearns, C.A., Inouye, D.W., Waser, N.M., 1998. Endangered mutualisms: the conservation of plant-pollinator interactions. Ann. Rev. Ecol. Syst. 29, 83–112. Kerr, J.T., Pindar, A., Galpern, P., Packer, L., Potts, S.G., Roberts, S.M., Rasmont, P., Schweiger, O., Colla, S.R., Richardson, L.L., Wagner, D.L., Gall, L.F., Sikes, D.S., Pantoja, A., 2015. Climate change impacts on bumblebees converge across continents. Science 349, 177–180. Klein, A.M., Vaissiere, B.E., Cane, J.H., Steffan-Dewenter, I., Cunningham, S.A., Kremen, C., Tscharntke, T., 2007. Importance of pollinators in changing landscapes for world crops. Proc. R. Soc. B 274, 303–313. Kojima, Y., Toki, T., Morimoto, T., Yoshiyama, M., Kimura, K., Kadowaki, T., 2011. Infestation of Japanese native honey bees by tracheal mite and virus from nonnative European honey bees in Japan. Microb. Ecol. 62, 895–906. Lauring, A.S., Andino, R., 2010. Quasispecies theory and the behavior of RNA viruses. PLoS Path. 6, e1001005. Levitt, A.L., Singh, R., Cox-Foster, D.L., Rajotte, E., Hoover, K., Ostiguy, N., Holmes, E. C., 2013. Cross-species transmission of honey bee viruses in associated arthropods. Virus Res. 176, 232–240. Li, J., Qin, H., Wu, J., Sadd, B.M., Wang, X., Evans, J.D., Peng, W.J., Chen, Y., 2012. The prevalence of parasites and pathogens in Asian honey bees Apis cerana. PLoS One 7, e47955. Li, J.L., Cornman, R.S., Evans, J.D., Pettis, J.S., Zhao, Y., Murphy, C., Peng, W.J., Wu, J., Hamilton, M., Boncristiani, H.F., Zhou, L., Hammond, J., Chen, Y.P., 2014. Systemic spread and propagation of a plant-pathogenic virus in European honey bees, Apis mellifera. mBio 5, e00898. Li, J.L., Peng, W.J., Wu, J., Strange, J.P., Boncristiani, H., Chen, Y.P., 2011. Cross-species infection of deformed wing virus poses a new threat to pollinator conservation. J. Econ. Entomol. 104, 732–739. Maori, E., Lavi, S., Mozes-Koch, R., Gantman, Y., Peretz, Y., Edelbaum, O., Tanne, E., Sela, I., 2007. Isolation and characterization of Israeli acute paralysis virus, a dicistrovirus affecting honeybees in Israel: evidence for diversity due to intraand inter-species recombination. J. Gen. Virol. 88, 3428–3438. Martin, S.J., Highfield, A.C., Brettell, L., Villalobos, E.M., Budge, G.E., Powell, M., Nikaido, S., Schroeder, D.C., 2012. Global honey bee viral landscape altered by a parasitic mite. Science 336, 1304–1306. Mayo, M.A., 2002a. A summary of taxonomic changes recently approved by ICTV. Arch. Virol. 147, 1655–1663. Mayo, M.A., 2002b. Virus taxonomy - Houston 2002. Arch. Virol. 147, 1071–1076. Mazzei, M., Carrozza, M.L., Luisi, E., Forzan, M., Giusti, M., Sagona, S., Tolari, F., Felicioli, A., 2014. Infectivity of DWV associated to flower pollen: experimental evidence of a horizontal transmission route. PLoS One 9, e113448. McMahon, D.P., Fürst, M.A., Caspar, J., Theodorou, P., Brown, M.J.F., Paxton, R.J., 2015. A sting in the spit: widespread cross-infection of multiple RNA viruses across wild and managed bees. J. Anim. Ecol. 84, 615–624. McMenamin, A.J., Genersch, E., 2015. Honey bee colony losses and associated viruses. Curr. Opin. Insect Sci. 8, 121–129. Meeus, I., de Miranda, J.R., de Graaf, D.C., Wackers, F., Smagghe, G., 2014. Effect of oral infection with Kashmir bee virus and Israeli acute paralysis virus on bumblebee (Bombus terrestris) reproductive success. J. Invertebr. Pathol. 121, 64–69. Meixner, M.D., Francis, R.M., Gajda, A., Kryger, P., Andonov, S., Uzunov, A., Topolska, G., Costa, C., Amiri, E., Berg, S., Bienkowska, M., Bouga, M., Büchler, R., Dyrba, W., Gurgulova, K., Hatjina, F., Ivanova, E., Janes, M., Kezic, N., Korpela, S., Conte, Y.L., Panasiuk, B., Pechhacker, H., Tsoktouridis, G., Vaccari, G., Wilde, J., 2014. Occurrence of parasites and pathogens in honey bee colonies used in a European genotype-environment interactions experiment. J. Apicultural Res. 53, 215–229. Möckel, N., Gisder, S., Genersch, E., 2011. Horizontal transmission of deformed wing virus (DWV): pathological consequences in adult bees (Apis mellifera) depend on the transmission route. J. Gen. Virol. 92, 370–377. Mondet, F., de Miranda, J.R., Kretzschmar, A., Le Conte, Y., Mercer, A.R., 2014. On the front line: quantitative virus dynamics in honey bee (Apis mellifera L.) colonies along a new expansion front of the parasite Varroa destructor. PloS Pathog 10, e1004323. Mookhploy, W., Kimura, K., Disayathanoowat, T., Yoshiyama, M., Hondo, K., Chantawannakul, P., 2015. Capsid gene divergence of black queen cell virus isolates in Thailand and Japan honey bee species. J. Econ. Entomol. 108, 1460– 1464. Mordecai, G.J., Wilfert, L., Martin, S.J., Jones, I.M., Schroeder, D.C., 2016. Diversity in a honey bee pathogen: first report of a third master variant of the Deformed Wing Virus quasispecies. ISME J. 10, 1264–1273. Moritz, R.F.A., Erler, S., 2016. Lost colonies found in a data mine: global honey trade but not pests or pesticides as a major cause of regional honeybee colony declines. Agric. Ecosyst. Environ. 216, 44–50. Navajas, M., Migeon, A., Alaux, C., Martin-Magniette, M.L., Robinson, G.E., Evans, J.D., Cros-Arteil, S., Crauser, D., Le Conte, Y., 2008. Differential gene expression of the honey bee Apis mellifera associated with Varroa destructor infection. BMC Genomics 9, 301. Nielsen, S.L., Nicolaisen, M., Kryger, P., 2008. Incidence of acute bee paralysis virus, black queen cell virus, chronic bee paralysis virus, deformed wing virus, Kashmir bee virus and sacbrood virus in honey bees (Apis mellifera) in Denmark. Apidologie 39, 310–314. Niu, J.Z., Smagghe, G., De Coninck, D.I.M., Van Nieuwerburgh, F., Deforce, D., Meeus, I., 2016. In vivo study of Dicer-2-mediated immune response of the small interfering RNA pathway upon systemic infections of virulent and avirulent viruses in Bombus terrestris. Insect Biochem. Mol. Biol. 70, 127–137. Nordstrom, S., Fries, I., Aarhus, A., Hansen, H., Korpela, S., 1999. Virus infections in Nordic honey bee colonies with no, low or severe Varroa jacobsoni infestations. Apidologie 30, 475–484. Olivier, V., Massou, I., Celle, O., Blanchard, P., Schurr, F., Ribiere, M., Gauthier, M., 2008. In situ hybridization assays for localization of the chronic bee paralysis virus in the honey bee (Apis mellifera) brain. J. Virol. Methods 153, 232–237. Ongus, J.R., Peters, D., Bonmatin, J.-M., Bengsch, E., Vlak, J.M., van Oers, M.M., 2004. Complete sequence of a picorna-like virus of the genus Iflavirus replicating in the mite Varroa destructor. J. Gen. Virol. 85, 3747–3755. Parmentier, L., Smagghe, G., de Graaf, D.C., Meeus, I., 2016. Varroa destructor Macula-like virus, Lake Sinai virus and other new RNA viruses in wild bumblebee hosts (Bombus pascuorum, Bombus lapidarius and Bombus pratorum). J. Invertebr. Pathol. 134, 6–11. Peng, W.J., Li, J., Boncristiani, H., Strange, J.P., Hamilton, M., Chen, Y., 2011. Host range expansion of honey bee black queen cell virus in the bumblebee, Bombus huntii. Apidologie 42, 650–658. Pitts-Singer, T., Cane, J.H., 2011. The alfalfa leafcutting bee, Megachile rotundata: the world’s most intensively managed solitary bee. Annu. Rev. Entomol. 56, 221– 237. Rana, R., Bana, B.S., Kaushal, N., Kumar, D., Kaundal, P., Rana, K., Khan, M.A., Gwande, S.J., Sharma, H.K., 2011. Identification of sacbrood virus disease in honeybee, Apis mellifera L. by using ELISA and RT-PCR techniques. Indian J. Biotechnol. 10, 274–284. Ravoet, J., De Smet, L., Meeus, I., Smagghe, G., Wenseleers, T., de Graaf, D.C., 2014. Widespread occurrence of honey bee pathogens in solitary bees. J. Invertebr. Pathol. 122, 55–58. Ravoet, J., De Smet, L., Wenseleers, T., de Graaf, D.C., 2015a. Genome sequence heterogeneity of Lake Sinai virus found in honey bees and Orf1/RdRP-based polymorphisms in a single host. Virus Res. 201, 67–72. Ravoet, J., De Smet, L., Wenseleers, T., de Graaf, D.C., 2015b. Vertical transmission of honey bee viruses in a Belgian queen breeding program. BMC Vet. Res. 11, 61. S. Gisder, E. Genersch / Journal of Invertebrate Pathology 147 (2017) 51–59 Ravoet, J., Maharramov, J., Meeus, I., De Smet, L., Wenseleers, T., Smagghe, G., de Graaf, D.C., 2013. Comprehensive bee pathogen screening in Belgium reveals Crithidia mellifica as a new contributory factor to winter mortality. PLoS One 8, e72443. Reddy, K.E., Noh, J.H., Choe, S.E., Kweon, C.H., Yoo, M.S., Doan, H.T.T., Ramya, M., Yoon, B.-S., Nguyen, L.T.K., Nguyen, T.T.D., Quyen, D.V., Jung, S.-C., Chang, K.-Y., Kang, S.W., 2013. Analysis of the complete genome sequence and capsid region of black queen cell viruses from infected honey bees (Apis mellifera) in Korea. Virus Genes 47, 126–132. Reddy, K.E., Yoo, M.S., Kim, Y.H., Kim, N.H., Ramya, M., Jung, H.N., Thao, L.T.B., Lee, H. S., Kang, S.W., 2016. Homology differences between complete sacbrood virus genomes from infected Apis mellifera and Apis cerana honey bees in Korea. Virus Genes 52, 281–289. Reynaldi, F.J., Sguazza, G.H., Albicoro, F.J., Pecoraro, M.R., Galosi, C.M., 2013. First molecular detection of co-infection of honey bee viruses in asymptomatic Bombus atratus in South America. Braz. J. Biol. 73, 797–800. Ribiere, M., Olivier, V., Blanchard, P., 2010. Chronic bee paralysis virus: a disease and a virus like no other? J. Invertebr. Pathol. 103, S120–S131. Ribiere, M., Triboulot, C., Mathieu, L., Aurières, C., Faucon, J.-P., Pepin, M., 2002. Molecular diagnosis of chronic bee paralysis virus infection. Apidologie 3, 339– 351. Roberts, J.M.K., Anderson, D.L., 2014. A novel strain of sacbrood virus of interest to world apiculture. J. Invertebr. Pathol. 118, 71–74. Runckel, C., Flenniken, M.L., Engel, J.C., Ruby, J.G., Ganem, D., Andino, R., DeRisi, J.L., 2011. Temporal analysis of the honey bee microbiome reveals four novel viruses and seasonal prevalence of known viruses, Nosema, and Crithidia. PLoS One 6, e20656. Sachman-Ruiz, B., Narvaez-Padilla, V., Reynaud, E., 2015. Commercial Bombus impatiens as reservoirs of emerging infectious diseases in central Mexico. Biol. Invasions 17, 2043–2053. Schöning, C., Gisder, S., Geiselhardt, S., Kretschmann, I., Bienefeld, K., Hilker, M., Genersch, E., 2012. Evidence for damage-dependent hygienic behaviour towards Varroa destructor parasitised brood in the western honey bee, Apis mellifera. J. Exp. Biol. 215, 264–271. Sedivy, C., Dorn, S., 2014. Towards a sustainable management of bees of the subgenus Osmia (Megachilidae; Osmia) as fruit tree pollinators. Apidologie 45, 88–105. Shen, M., Yang, X., Cox-Foster, D., Cui, L., 2005. The role of varroa mites in infections of Kashmir bee virus (KBV) and deformed wing virus (DWV) in honey bees. Virology 342, 141–149. Shutler, D., Head, K., Burgher-MacLellan, K.L., Colwell, M.J., Levitt, A.L., Ostiguy, N., Williams, G.R., 2014. Honey bee Apis mellifera parasites in the absence of Nosema ceranae fungi and Varroa destructor mites. PLoS One 9, e98599. Singh, R., Levitt, A.L., Rajotte, E.G., Holmes, E.C., Ostiguy, N., Vanengelsdorp, D., Lipkin, W.I., Depamphilis, C.W., Toth, A.L., Cox-Foster, D.L., 2010. RNA viruses in hymenopteran pollinators: evidence of inter-Taxa virus transmission via pollen and potential impact on non-Apis hymenopteran species. PLoS One 5, e14357. Sommeijer, M., 1999. Beekeeping with stingless bees: a new type of hive. Bee World 80, 70–79. Soroker, V., Hetzroni, A., Yakobson, B., David, D., David, A., Voet, H., Slabezki, Y., Efrat, H., Levski, S., Kamer, Y., Klinberg, E., Zioni, N., Inbar, S., Chejanovsky, N., 2011. Evaluation of colony losses in Israel in relation to the incidence of pathogens and pests. Apidologie 42, 192–199. Tapaszti, Z., Forgách, P., Kovágó, C., Topolska, G., Nowotny, N., Rusvai, M.T.B., 2009. Genetic analysis and phylogenetic comparison of black queen cell virus genotypes. Vet. Microbiol. 139, 227–234. 59 Tehel, A., Brown, M.J.F., Paxton, R.J., 2016. Impact of managed honey bee viruses on wild bees. Curr. Opin. Virol. 19, 16–22. Tentcheva, D., Gauthier, L., Zappulla, N., Dainat, B., Cousserans, F., Colin, M.E., Bergoin, M., 2004. Prevalence and seasonal variations of six bee viruses in Apis mellifera L. and Varroa destructor mite populations in France. Appl. Environ. Microbiol. 70, 7185–7191. Topolska, G., Ball, B., Allen, M., 1995. Identification of viruses in bees from two Warsaw apiaries. Medycyna Weterynaryjna 51, 145–147. Ueira-Vieira, C., Almeida, L.O., de Almeida, F.C., Amaral, I.M.R., Brandeburgo, M.A.M., Bonetti, A.M., 2015. Scientific note on the first molecular detection of the acute bee paralysis virus in Brazilian stingless bees. Apidologie 46, 628–630. vanEngelsdorp, D., Evans, J.D., Saegerman, C., Mullin, C., Haubruge, E., Nguyen, B.K., Frazier, M., Frazier, J., Cox-Foster, D., Chen, Y., Underwood, R., Tarpy, D.R., Pettis, J.S., 2009. Colony collapse disorder: a descriptive study. PLoS One 4, e6481. vanEngelsdorp, D., Meixner, M.D., 2010. A historical review of managed honey bee populations in Europe and the United States and the factors that may affect them. J. Invertebr. Pathol. 103, S80–S95. Velthuis, H.H.W., van Doorn, A., 2006. A century of advances in bumblebee domestication and the economic and environmental aspects of its commercialization for pollination. Apidologie 37, 421–451. Wang, T.-S., Shi, T.-F., Liu, F., Yu, L.-S., Qi, L., Meng, X.-J., 2015. Occurrence and distribution of seven bee viruses in Apis mellifera and Apis cerana in Anhui Province, China. Chin. J. Appl. Entomol. 52, 324–332. Wilfert, L., Long, G., Leggett, H.C., Schmid-Hempel, P., Butlin, R., Martin, S.J.M., Boots, M., 2016. Deformed wing virus is a recent global epidemic in honeybees driven by Varroa mites. Science 351, 594–597. Yang, X., Cox-Foster, D.L., 2005. Impact of an ectoparasite on the immunity and pathology of an invertebrate: evidence for host immunosuppression and viral amplification. Proc. Natl. Acad. Sci. USA 102, 7470–7475. Yue, C., Genersch, E., 2005. RT-PCR analysis of Deformed wing virus in honeybees (Apis mellifera) and mites (Varroa destructor). J. Gen. Virol. 86, 3419–3424. Yue, C., Schroder, M., Gisder, S., Genersch, E., 2007. Vertical-transmission routes for deformed wing virus of honeybees (Apis mellifera). J. Gen. Virol. 88, 2329–2336. Zhang, H., Huang, J., Williams, P.H., Vaissière, B.E., Zhou, Z., Gai, Q., Dong, J., An, J., 2015. Managed bumblebees outperform honey bees in increasing peach fruit set in China: different limiting processes with different pollinators. PLoS One 10, e0121143. Zhang, Q.S., Ongus, J.R., Boot, W.J., Calls, J., Bonmatin, J.M., Bengsch, E., Peters, D., 2007. Detection and localisation of picorna-like virus particles in tissues of Varroa destructor, an ectoparasite of the honey bee, Apis mellifera. J. Invertebr. Pathol. 96, 97–105. Zhang, X., He, S.Y., Evans, J.D., Pettis, J.S., Yin, G.F., Chen, Y.P., 2012. New evidence that deformed wing virus and black queen cell virus are multi-host pathogens. J. Invertebr. Pathol. 109, 156–159. Zhang, Y., Huang, X., Xu, Z.F., Han, R.C., Chen, J.H., 2013. Differential gene transcription in honey bee (Apis cerana) larvae challenged by Chinese sacbrood virus (CSBV). Sociobiology 60, 413–420. Zhang, Y., Liu, X.J., Zhang, W.Q., Han, R.C., 2010. Differential gene expression of the honey bees Apis mellifera and A. cerana induced by Varroa destructor infection. J. Insect Physiol. 56, 1207–1218. Zioni, N., Soroker, V., Chejanovsky, N., 2011. Replication of Varroa destructor virus 1 (VDV-1) and a Varroa destructor-1–deformed wing virus recombinant (VDV-1– DWV) in the head of the honey bee. Virology 417, 106–112.