Jorgen Ravoet

Comprehensive Bee Pathogen Screening in Belgium Reveals Crithidia mellificae as a New Contributory Factor to Winter Mortality

Since the last decade, unusually high honey bee colony losses have been reported mainly in North-America and Europe. Here, we report on a comprehensive bee pathogen screening in Belgium covering 363 bee colonies that were screened for 18 known disease-causing pathogens and correlate their incidence in summer with subsequent winter mortality. Our analyses demonstrate that, in addition to Varroa destructor, the presence of the trypanosomatid parasite Crithidia mellificae and the microsporidian parasite Nosema ceranae in summer are also predictive markers of winter mortality, with a negative synergy being observed between the two in terms of their effects on colony mortality. Furthermore, we document the first occurrence of a parasitizing phorid fly in Europe, identify a new fourth strain of Lake Sinai Virus (LSV), and confirm the presence of other little reported pathogens such as Apicystis bombi, Aphid Lethal Paralysis Virus (ALPV), Spiroplasma apis, Spiroplasma melliferum and Varroa destructor Macula-like Virus (VdMLV). Finally, we provide evidence that ALPV and VdMLV replicate in honey bees and show that viruses of the LSV complex and Black Queen Cell Virus tend to non-randomly co-occur together. We also noticed a significant correlation between the number of pathogen species and colony losses. Overall, our results contribute significantly to our understanding of honey bee diseases and the likely causes of their current decline in Europe.

Characterization of Two Species of Trypanosomatidae from the Honey Bee Apis mellifera: Crithidia mellificae Langridge and McGhee, † and Lotmaria passim n. gen., n. sp.

Trypanosomatids are increasingly recognized as prevalent in European honey bees (Apis mellifera) and by default are attributed to one recognized species, Crithidia mellificae Langridge and McGhee, 1967. We provide reference genetic and ultrastructural data for type isolates of C. mellificae (ATCC 30254 and 30862) in comparison with two recent isolates from A. mellifera (BRL and SF). Phylogenetics unambiguously identify strains BRL/SF as a novel taxonomic unit distinct from C. mellificae strains 30254/30862 and assign all four strains as lineages of a novel clade within the subfamily Leishmaniinae. In vivo analyses show strains BRL/SF preferably colonize the hindgut, lining the lumen as adherent spheroids in a manner identical to previous descriptions from C. mellificae. Microscopy images show motile forms of C. mellificae are distinct from strains BRL/SF. We propose the binomial Lotmaria passim n. gen., n. sp. for this previously undescribed taxon. Analyses of new and previously accessioned genetic data show C. mellificae is still extant in bee populations, however, L. passim n. gen., n. sp. is currently the predominant trypanosomatid in A. mellifera globally. Our findings require that previous reports of C. mellificae be reconsidered and that subsequent trypanosomatid species designations from Hymenoptera provide genetic support.

Widespread occurrence of honey bee pathogens in solitary bees

Solitary bees and honey bees from a neighbouring apiary were screened for a broad set of putative pathogens including protists, fungi, spiroplasmas and viruses. Most sampled bees appeared to be infected with multiple parasites. Interestingly, viruses exclusively known from honey bees such as Apis mellifera Filamentous Virus and Varroa destructor Macula-like Virus were also discovered in solitary bees. A microsporidium found in Andrena vaga showed most resemblance to Nosema thomsoni. Our results suggest that bee hives represent a putative source of pathogens for other pollinators. Similarly, solitary bees may act as a reservoir of honey bee pathogens.

BeeDoctor, a versatile MLPA-based diagnostic tool for screening bee viruses.

The long-term decline of managed honeybee hives in the world has drawn significant attention to the scientific community and bee-keeping industry. A high pathogen load is believed to play a crucial role in this phenomenon, with the bee viruses being key players. Most of the currently characterized honeybee viruses (around twenty) are positive stranded RNA viruses. Techniques based on RNA signatures are widely used to determine the viral load in honeybee colonies. High throughput screening for viral loads necessitates the development of a multiplex polymerase chain reaction approach in which different viruses can be targeted simultaneously. A new multiparameter assay, called “BeeDoctor”, was developed based on multiplex-ligation probe dependent amplification (MLPA) technology. This assay detects 10 honeybee viruses in one reaction. “BeeDoctor” is also able to screen selectively for either the positive strand of the targeted RNA bee viruses or the negative strand, which is indicative for active viral replication. Due to its sensitivity and specificity, the MLPA assay is a useful tool for rapid diagnosis, pathogen characterization, and epidemiology of viruses in honeybee populations. “BeeDoctor” was used for screening 363 samples from apiaries located throughout Flanders; the northern half of Belgium. Using the “BeeDoctor”, virus infections were detected in almost eighty percent of the colonies, with deformed wing virus by far the most frequently detected virus and multiple virus infections were found in 26 percent of the colonies.

Pesticides for Apicultural and/or Agricultural Application Found in Belgian Honey Bee Wax Combs

In a Belgian pilot study honey bee wax combs from ten hives were analyzed on the presence of almost 300 organochlorine and organophosphorous compounds by LC–MS/MS and GC–MS/MS. Traces of 18 pesticides were found and not a single sample was free of residues. The number of residues found per sample ranged from 3 to 13, and the pesticides found could be categorized as (1) pesticides for solely apicultural (veterinary) application, (2) pesticides for solely agricultural (crop protection) application, (3) pesticides for mixed agricultural and apicultural (veterinary) application. The frequencies and quantities of some environmental pollutants bear us high concerns. Most alarming was the detection of lindane (gamma-HCH) and dichlorodiphenyltrichloroethane (including its breakdown product dichlorodiphenyldichloroethylene), two insecticides that are banned in Europe. The present comprehensive residue analysis, however, also reveals residues of pesticides never found in beeswax before, i.e. DEET, propargite and bromophos.

Holistic screening of collapsing honey bee colonies in Spain: a case study

BackgroundHere we present a holistic screening of collapsing colonies from three professional apiaries in Spain. Colonies with typical honey bee depopulation symptoms were selected for multiple possible factors to reveal the causes of collapse.ResultsOmnipresent were Nosema ceranae and Lake Sinai Virus. Moderate prevalences were found for Black Queen Cell Virus and trypanosomatids, whereas Deformed Wing Virus, Aphid Lethal Paralysis Virus strain Brookings and neogregarines were rarely detected. Other viruses, Nosema apis, Acarapis woodi and Varroa destructor were not detected. Palinologic study of pollen demonstrated that all colonies were foraging on wild vegetation. Consequently, the pesticide residue analysis was negative for neonicotinoids. The genetic analysis of trypanosomatids GAPDH gene, showed that there is a large genetic distance between Crithidia mellificae ATCC30254, an authenticated cell strain since 1974, and the rest of the presumed C. mellificae sequences obtained in our study or published. This means that the latter group corresponds to a highly differentiated taxon that should be renamed accordingly.ConclusionThe results of this study demonstrate that the drivers of colony collapse may differ between geographic regions with different environmental conditions, or with different beekeeping and agricultural practices. The role of other pathogens in colony collapse has to bee studied in future, especially trypanosomatids and neogregarines. Beside their pathological effect on honey bees, classification and taxonomy of these protozoan parasites should also be clarified.

Bee pathogens found in Bombus atratus from Colombia: A case study.

Bombus atratus bumblebees from Colombia that were caught in the wild and from breeding programs were screened for a broad set of bee pathogens. We discovered for the first time Lake Sinai Virus and confirmed the infection by other common viruses. The prevalence of Apicystis bombi, Crithidia bombi and Nosema ceranae was remarkably high. According to other studies the former two could have been co-introduced in South America with exotic bumble bees as Bombus terrestris or Bombus ruderatus. Given the fact that none of these species occur in Colombia, our data puts a new light on the spread of these pathogens over the South American continent.

Genome sequence heterogeneity of Lake Sinai Virus found in honey bees and Orf1/RdRP-based polymorphisms in a single host

Honey bees (Apis mellifera) are susceptible to a wide range of pathogens, including a broad set of viruses. Recently, next-generation sequencing has expanded the list of viruses with, for instance, two strains of Lake Sinai Virus. Soon after its discovery in the USA, LSV was also discovered in other countries and in other hosts. In the present study, we assemble four almost complete LSV genomes, and show that there is remarkable sequence heterogeneity based on the Orf1, RNA-dependent RNA polymerase and capsid protein sequences in comparison to the previously identified LSV 1 and 2 strains. Phylogenetic analyses of LSV sequences obtained from single honey bee specimens further revealed that up to three distinctive clades could be present in a single bee. Such superinfections have not previously been identified for other honey bee viruses. In a search for the putative routes of LSV transmission, we were able to demonstrate the presence of LSV in pollen pellets and in Varroa destructor mites. However, negative-strand analyses demonstrated that the virus only actively replicates in honey bees and mason bees (Osmia cornuta) and not in Varroa mites.

Differential diagnosis of the honey bee trypanosomatids Crithidia mellificae and Lotmaria passim

Trypanosomatids infecting honey bees have been poorly studied with molecular methods until recently. After the description of Crithidia mellificae (Langridge and McGhee, 1967) it took about forty years until molecular data for honey bee trypanosomatids became available and were used to identify and describe a new trypanosomatid species from honey bees, Lotmaria passim (Evans and Schwarz, 2014). However, an easy method to distinguish them without sequencing is not yet available. Research on the related bumble bee parasites Crithidia bombi and Crithidia expoeki revealed a fragment length polymorphism in the internal transcribed spacer 1 (ITS1), which enabled species discrimination. In search of fragment length polymorphisms for differential diagnostics in honey bee trypanosomatids, we studied honey bee trypanosomatid cell cultures of C. mellificae and L. passim. This research resulted in the identification of fragment length polymorphisms in ITS1 and ITS1-2 markers, which enabled us to develop a diagnostic method to differentiate both honey bee trypanosomatid species without the need for sequencing. However, the amplification success of the ITS1 marker depends probably on the trypanosomatid infection level. Further investigation confirmed that L. passim is the dominant species in Belgium, Japan and Switzerland. We found C. mellificae only rarely in Belgian honey bee samples, but not in honey bee samples from other countries. C. mellificae was also detected in mason bees (Osmia bicornis and Osmia cornuta) besides in honey bees. Further, the characterization and comparison of additional markers from L. passim strain SF (published as C. mellificae strain SF) and a Belgian honey bee sample revealed very low divergence in the 18S rRNA, ITS1-2, 28S rRNA and cytochrome b sequences. Nevertheless, a variable stretch was observed in the gp63 virulence factor.

Vertical transmission of honey bee viruses in a Belgian queen breeding program

BackgroundThe Member States of European Union are encouraged to improve the general conditions for the production and marketing of apicultural products. In Belgium, programmes on the restocking of honey bee hives have run for many years. Overall, the success ratio of this queen breeding programme has been only around 50%. To tackle this low efficacy, we organized sanitary controls of the breeding queens in 2012 and 2014.ResultsWe found a high quantity of viruses, with more than 75% of the egg samples being infected with at least one virus. The most abundant viruses were Deformed Wing Virus and Sacbrood Virus (≥40%), although Lake Sinai Virus and Acute Bee Paralysis Virus were also occasionally detected (between 10-30%). In addition, Aphid Lethal Paralysis Virus strain Brookings, Black Queen Cell Virus, Chronic Bee Paralysis Virus and Varroa destructor Macula-like Virus occurred at very low prevalences (≤5%). Remarkably, we found Apis mellifera carnica bees to be less infected with Deformed Wing Virus than Buckfast bees (p < 0.01), and also found them to have a lower average total number of infecting viruses (p < 0.001). This is a significant finding, given that Deformed Wing Virus has earlier been shown to be a contributory factor to winter mortality and Colony Collapse Disorder. Moreover, negative-strand detection of Sacbrood Virus in eggs was demonstrated for the first time.ConclusionsHigh pathogen loads were observed in this sanitary control program. We documented for the first time vertical transmission of some viruses, as well as significant differences between two honey bee races in being affected by Deformed Wing Virus. Nevertheless, we could not demonstrate a correlation between the presence of viruses and queen breeding efficacies.