Worker bees normally serve as a colony's first line of defense against contamination, filtering harmful substances before they can spread through the hive. But new research shows that queen bees also have a defense of their own. When honeybee queens are exposed to pesticides over time, some of those chemicals can accumulate in their bodies and then be transferred into their eggs.
Researchers call this process maternal offloading. The findings, published in Current Biology, provide the first evidence in honeybees of how far a queen may go to reduce her own chemical burden. The research was led by the University of California, Davis.
"In order to protect herself, the queen bee offloads these chemicals into her eggs to get rid of them," said Sascha Nicklisch, the paper's senior author and an associate professor in the Department of Environmental Toxicology. "No one has shown this in honeybees before." The results suggest that pesticides may continue accumulating in a colony even after exposure begins, especially once worker bees are no longer able to remove contaminants as effectively. That could have implications for beekeepers, growers and integrated-pest-management planners, particularly during periods when bees are actively foraging or colonies are expanding.
The study was carried out in collaboration with Lawrence Livermore National Laboratory, or LLNL, and the U.S. Department of Agriculture's Agricultural Research Service, or USDA-ARS. "When pesticides accumulate to the extent that the queen bee has eggs that are so loaded they may no longer develop properly, there could be a tipping point," Nicklisch said.
"There may be a slow creeping effect of chemical accumulation that will contribute to delayed colony collapse." Most previous toxicology research involving honeybees has centered on worker bees. This study instead followed where chemicals ended up throughout the colony and examined their effects on the queen, her ovaries, her eggs, and the wax. Worker bees normally feed and care for both queens and developing larvae.
Scientists have long thought that worker bees help shield queens from contamination by filtering harmful substances out of the food they provide. The new findings indicate that this protection may only work up to a point, said Angela Encerrado-Manriquez, the paper's lead author and a recent Ph.D. graduate from UC Davis. "In our study, pesticides began to accumulate in queens over time, suggesting that worker filtration capacity can be overwhelmed," Encerrado-Manriquez said.
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