Feed supplementation with molybdenum complexes improves honey bee health

This study investigates the effects of dietary supplementation with molybdenum-based compounds on honey bee health. Among a series of dinuclear Mo(v) complexes, the most stable and non-toxic complexes were selected and tested over an extensive eight-year field campaign involving more than 700 beehives across diverse environmental conditions in Moldova, France, Greece and the United States. In a first part, we established that the administration of a few milligrams of the compounds Na-Mo2O4-EDTA or Li-Mo2O4-EDTA in spring or autumn enhanced colony performance: queen fecundity, hygienic behaviour, and honey production increased, while Varroa destructor infestation rates and winter losses were substantially reduced. A second part of the work focused on understanding these effects in beehives. Hive monitoring showed that the Mo-containing syrup can be consumed over 1.5 months and is well assimilated by larvae and workers. 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 the brain, neurolemma and hypopharyngeal glands, which play a crucial role in honey bee health. The metabolism of Mo complexes was addressed using X-ray photoelectron spectroscopy (XPS) on bee f ae ces, which revealed that the complexes are oxidized into Mo(vi), suggesting that Mo complexes may function as antioxidant agents in bees. These findings offer promising solutions for the beekeeping industry, struggling with weakening honey bee colonies.