Abstract
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.
Highlights
Pollination is vital to the functioning of natural ecosystems, boosting the reproduction of wild plants, on which many other organisms depend
The protozoan C. mellificae has been ignored for a long time, but the current data highlight it as a new putative key player in honey bee colony declines
The present study extends the number of pathogens bees are exposed to in Europe, and assigned the trypanosomid parasite C. mellificae as a new contributory factor to explain winter losses, in addition to the parasitic mite V. destructor and the microsporidian parasite N. ceranae
Summary
Pollination is vital to the functioning of natural ecosystems, boosting the reproduction of wild plants, on which many other organisms depend. The ectoparasitic mite Varroa destructor is almost certainly a key player in causing the observed elevated colony losses [6,7,8,9,10,11] This mite jumped from the Asian honey bee (Apis cerana) to the European honey bee (Apis mellifera) more than fifty years ago and has since become an almost cosmopolitan pest [12]. The mite weakens the bees by sucking hemolymph from both adult bees and pupae [13] They can transmit many of the known honey bee viruses [14,15,16,17,18] and cause a reactivation of covert virus infections due to host immune suppression [19]. V. destructor and Deformed Wing Virus (DWV) will reduce the life span of winter bees, which can cause a colony collapse [21]
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