Feed supplementation with molybdenum complexes improves honey bee health

In this study, we evaluated the impact of supplementing honey bee feed with molybdenum-based compounds. Among a dozen of dinuclear Mo(V) complexes, we first selected the most stable and non-toxic complexes, which were tested as food supplements in an extensive eight-year campaign involving more than 700 beehives across various environmental conditions in Moldova, France, Greece and USA. This unprecedented field campaign revealed that a few milligrams of compounds Na-Mo2O4-EDTA or Li-Mo2O4-EDTA provided in spring or autumn, increased queen fecundity, hygienic behavior, and honey production, while infestation rates of worker bees and brood by the mite Varroa destructor, and mortality rates in winter were dramatically reduced. Hive monitoring showed that the Mo-containing syrup can be consumed over 1.5 months and is well assimilated by larvae and workers within the hive. In particular, Mo levels increased significantly in the head of the bees. X-ray fluorescence measurements demonstrated that Na-Mo2O4-EDTA increases Mo levels in brain, neurolemma and hypopharyngeal glands. The metabolism of Mo complexes was addressed using X-Ray photoelectron spectroscopy (XPS) on bee faeces, which revealed that the complexes are oxidized into Mo(VI) species and thus suggesting that Mo complexes may function as antioxidant agents in bees. These findings offer promising solutions for the beekeeping industry, which is struggling with weakening honey bee colonies.