Comprehensive Bee Pathogen Screening in Belgium Reveals Crithidia mellificae as a New Contributory Factor to Winter Mortality
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.
Crithidia are members of the trypanosome protozoa. They are parasites that exclusively parasitise arthropods, mainly insects. They pass from host to host as cysts in infective faeces and typically, the parasites develop in the digestive tracts of insects and interact with the intestinal epithelium using their flagellum. They display very low host-specificity and a single parasite can infect a large range of invertebrate hosts. At different points in its life-cycle, it passes through amastigote, promastigote, and epimastigote phases; the last is particularly characteristic, and similar stages in other trypanosomes are often called crithidial.
Crithidia bombi is perhaps the most well documented species and is a parasite of bumblebees. Crithidia mellificae, is a parasite of the bee. Other species include C. fasciculata, C. deanei, C. desouzai, C. oncopelti, C. guilhermei and C. luciliae. C. deanei is atypical of the Crithidia genus, and it has been argued not a member of the Crithidia at all. It is also not typical of trypanosomatids because of its unusual shape and it harbours endosymbiotic bacteria. C. luciliae is the substrate for the antinuclear antibody test used to diagnose lupus and other autoimmune disorders
These parasites may be at least partially responsible for declining wild bee populations. They cause the bees to lose their ability to distinguish between flowers that contain nectar and those that don't. They make many mistakes by visiting nectar scarce flowers and in so doing, slowly starve to death.