Study reveals how contamination can increase within colonies.
Inside a honeybee colony, worker bees act as living filters. They intercept much of the pesticide contamination entering the hive, helping shield the queen and the developing young she produces. But when exposure continues and that protective system begins to fail, the queen may redirect the chemical burden into her own eggs.
Researchers call this process maternal offloading. It allows the queen to remove contaminants from her body by transferring them to her offspring, a survival strategy that could expose the colony’s next generation to pesticides before development is complete.
University of California, Davis researchers documented this response in honeybees for the first time. Their findings were published in Current Biology.
“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 discovery helps explain how pesticide contamination may persist and spread through a colony after worker bees lose their ability to remove enough of it. The results could influence decisions made by beekeepers, growers and integrated-pest-management planners, particularly when colonies are expanding or bees are actively foraging.
The research brought together scientists from UC Davis, Lawrence Livermore National Laboratory, or LLNL, and the U.S. Department of Agriculture’s Agricultural Research Service, or USDA-ARS.
Queens inherit a hidden burden
“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 honeybee toxicology studies have concentrated on worker bees, which are more likely to encounter pesticides while gathering food outside the hive. This investigation followed the chemicals deeper into the colony to determine where they accumulated and whether they reached the queen, her ovaries, her eggs and the wax surrounding them.
That broader view mattered because worker bees control what the queen eats. They collect and process food, then feed both the queen and developing larvae. This arrangement has long been thought to protect the colony’s reproductive center by filtering contaminants before they reach her.
Angela Encerrado-Manriquez, the paper’s lead author and a recent Ph.D. graduate from UC Davis, said the results revealed that this protection has a limit.
“In our study, pesticides began to accumulate in queens over time, suggesting that worker filtration capacity can be overwhelmed,” Encerrado-Manriquez said. “When this happens, queens have their own defense. Maternal offloading allows them to shunt the toxic burden to their eggs.”
Nanocolonies trace pesticide movement
To follow contamination through a colony under controlled conditions, the researchers built small experimental hives known as “nanocolonies.” Each one consisted of a conical plastic container with a netted bottom and housed one queen with 60 worker bees.
These simplified colonies reproduced essential hive functions while allowing the researchers to track where a pesticide moved. The bees received pollen, water, and food containing methyl parathion, a pesticide marked with a low-level radioactive tracer. The marker acted like a chemical tracking label, making tiny amounts of the pesticide detectable wherever they accumulated.
During the first day, workers removed 95% of the pesticide from the queen’s food and deposited it in the honeycomb. By day 10, however, their filtration rate had dropped to 86%, showing that continued exposure was gradually overwhelming this defense.
The study depended on different areas of expertise. USDA scientists contributed their knowledge of honeybee biology and experimental design, while LLNL researchers measured the radioactive marker at extremely small concentrations using biological accelerator spectrometry, or BioAMS. This method counts rare marked atoms, allowing researchers to trace amounts too small for many conventional instruments to detect.
“With BioAMS, we can trace very low levels of a pesticide,” said Bruce Buchholz, an LLNL scientist and author on the paper. “The pesticide concentrations we used were not lethal and were environmentally relevant to that seen in nature.”
Contamination reaches future workers
A honeybee queen can produce between 1,500 and 2,000 eggs each day. Those eggs supply the colony with future workers, making the queen’s reproductive health essential to the survival of the hive.
Honeybee colonies also help pollinate about one-third of the world’s food crops. When colonies weaken or disappear, the effects can reach beyond the hive by reducing agricultural productivity and threatening food security.
“The queen is the only member of the hive who can lay eggs that become the next generation of workers,” Nicklisch said. “She keeps the colony alive, so understanding how pesticides can affect queen bees and also her offspring is important.”
The findings leave several questions unresolved. Researchers still need to determine how long queens continue transferring contaminants into their eggs, whether the process produces lasting harm across the colony, and whether different pesticides create the same response.
Reference: “Queen bees offload pesticide burden to eggs when social buffering is overwhelmed” by Angela M. Encerrado-Manriquez, Julia D. Fine, Eliza Litsey, David Baliu-Rodriguez, Sean Patrick Leonard, Bruce A. Buchholz and Sascha C.T. Nicklisch, 2 July 2026, Current Biology.
DOI: 10.1016/j.cub.2026.06.022
The USDA’s National Institute of Food and Agriculture and Non-Assistance Cooperative Agreement program supported the research, as did the PAm-Costco USA Scholarship program and the University of California National Laboratory Fees Research Program. The work at LLNL is under a U.S. Department of Energy contract.
Never miss a breakthrough: Join the SciTechDaily newsletter.
Follow us on Google and Google News.