Investigations on the oxalic acid content of honey from oxalic acid treated and untreated bee colonies

Varroa destructor, an ectoparasitic mite, is one of the major pests of honeybees in many parts of the world. In order to keep bee colonies alive and productive, effective biological, biotechnical, or acaricidal control measures are necessary. Oxalic acid is one substance under discussion to replace synthetic acaricides (e.g. pyrethroids, organophosphates) to minimize the risk of residues in bee products. The application of oxalic acid based solutions (Bienenwohl or a self-prepared oxalic acid solution with sugar) to control Varroa destructor resulted in no relevant changes in the oxalic acid content of honey produced the following year, compared with honey samples from untreated colonies from the same location. The range of oxalic acid content in honey was 5-68 mg/kg in oxalic acid treated and 5-65 mg/kg in untreated colonies. The oxalic acid content of the honey was positively correlated with its electrical conductivity and thus with its original nectar or honeydew source.