Queen bees transfer pesticides to eggs to protect themselves, study finds

A honeybee queen, faced with a body accumulating pesticides faster than she can safely carry them, has found a way out: she dumps the toxins into her eggs. Researchers at UC Davis have documented this process for the first time in honeybees, calling it maternal offloading, and the discovery raises an uncomfortable question about what happens when a queen's own survival strategy becomes a threat to her colony's future.

The finding emerged from work published in Current Biology, a collaboration between UC Davis, Lawrence Livermore National Laboratory, and the USDA's Agricultural Research Service. Scientists exposed honeybee colonies to the pesticide methyl parathion—at levels they say are realistic to what bees encounter in nature—and tracked where the chemical went using radioactive markers. What they found was a system of protection that works, up to a point, and then fails. Worker bees, it turns out, do filter harmful substances from the food they provide to their queen. On the first day of exposure, they removed 95 percent of the pesticide from what the queen consumed, transferring the contamination into the honeycomb. But by day ten, that filtration capacity had dropped to 86 percent. The workers were becoming overwhelmed.

When the worker bees could no longer keep pace, the queen's body took over. She began offloading the accumulated pesticides directly into her eggs—a mechanism no one had previously documented in honeybees. Sascha Nicklisch, the senior author and an associate professor in environmental toxicology at UC Davis, described it plainly: the queen was protecting herself by passing the chemical burden to her developing offspring. It is, in a sense, a survival strategy that trades the queen's health for the health of the next generation.

The implications ripple outward. A honeybee queen produces between 1,500 and 2,000 eggs every single day. Those eggs become the workers that keep the hive alive. If those eggs are saturated with pesticides, they may fail to develop properly. Nicklisch warned of a potential tipping point—a moment when chemical accumulation reaches a threshold and the colony begins to collapse, not suddenly, but slowly, a creeping decline that could be difficult to detect until it is too late.

To conduct the research, scientists built small experimental systems called nanocolonies, each containing one queen and 60 worker bees, and fed them contaminated pollen and food. They used a specialized technique called biological accelerator spectrometry, or BioAMS, developed at Lawrence Livermore, to detect the pesticide at extremely low concentrations. The technology allowed them to trace the chemical's path through the colony with precision.

Angela Encerrado-Manriquez, the lead author and a recent Ph.D. graduate from UC Davis, emphasized that the worker bee protection system has limits. Once those limits are exceeded, the queen has no choice but to protect herself, even if it means loading her eggs with toxins. The question now is how long this can continue, what the long-term damage to colonies might be, and whether different pesticides trigger the same response. Those answers remain unknown.

The stakes are substantial. Honeybees pollinate roughly one-third of the world's food crops. Colony losses threaten agricultural productivity and food security. Understanding how pesticides move through a hive and affect the queen—the only bee capable of laying eggs that become workers—is essential to protecting the colonies we depend on. The research suggests that the invisible accumulation of chemicals in a hive may be a slower, quieter threat than anyone previously understood.