Queen Bees Offload Pesticides Into Their Eggs to Protect Themselves, Study Finds

Researchers led by the University of California, Davis, have found the first evidence in honeybees that queens can offload pesticides that build up in their bodies into their own eggs, a process the team calls maternal offloading, potentially passing the chemical burden on to the next generation. The findings were published in the journal Current Biology.

Worker bees normally act as a colony's first line of defense, filtering harmful substances out of food before they spread through the hive. To study what happens once that filtering is overwhelmed, the team, working with Lawrence Livermore National Laboratory and the US Department of Agriculture's Agricultural Research Service, built small experimental "nanocolonies," each with one queen and 60 worker bees, and fed them pollen, water and food contaminated with the pesticide methyl parathion, tagged with a low-level radioactive marker to trace where it moved.

On the first day, worker bees filtered out 95% of the pesticide and transferred it into the honeycomb; by day 10, that figure had dropped to 86%, indicating that worker filtration capacity can be overwhelmed over time. As pesticides continued accumulating, some chemicals built up in the queen's body and were then transferred into her eggs.

"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," said senior author Sascha Nicklisch, an associate professor in UC Davis's Department of Environmental Toxicology, adding that this could contribute to delayed colony collapse. Honeybee queens can lay 1,500 to 2,000 eggs a day, and honeybees pollinate about a third of the world's food crops, making colony losses a concern for both agriculture and food security. The researchers said they do not yet know how long queens can keep transferring contaminants into their eggs or what the long-term consequences for a colony might be.