Effect of contamination and adulteration of wax foundations on the brood development of honeybees

Various reports recently informed about the effects of contaminated or adulterated wax foundations as a main cause of poor brood and colony development. Beekeepers reported that affected colonies were showing a holey brood pattern and a decline in population size. Twenty-five samples of wax foundations were collected from different sources in Germany. Samples were analyzed using a multi-residue analysis for 147 insecticides, acaricides, and varroacides to investigate the actual load of contamination in beeswax. Furthermore, the effect of selected contaminated and/or adulterated wax foundations on colony and brood development of honeybees was evaluated under field conditions. Our results show that 38 active substances in total were found in the wax samples. Acaricides used in-hive were the most frequently detected contaminants at high concentrations. Trace concentrations of plant protection products and biocides were also found. In the field trials, a significant influence of stearin-adulterated wax on population size, the number of capped brood cells, and termination rate was found compared with the reference. No detectable effects of other treatments on the investigated parameters were observed.