Honeybee queens transfer pesticides to eggs for self-protection, study reveals

A study published on July 2, 2026, in Current Biology reveals that honeybee queens can transfer pesticides to their eggs, prioritizing their own survival over that of their offspring. Conducted by researchers at the University of California, Davis, this groundbreaking research highlights a process known as maternal offloading.

Understanding Maternal Offloading in Honeybees

Maternal offloading occurs when a honeybee queen exposed to pesticides passes those chemicals into her eggs. According to Sascha Nicklisch, the paper's senior author and an associate professor in the Department of Environmental Toxicology, “In order to protect herself, the queen bee offloads these chemicals into her eggs to get rid of them.” This phenomenon marks the first documentation of such behavior in honeybees.

The implications of this research extend beyond individual bees. As pesticides accumulate in queens, they can potentially lead to developmental issues in the eggs, thereby jeopardizing the health of entire colonies. “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 noted.

The Impact of Pesticides on Bee Colonies

Historically, toxicology studies on honeybees have focused primarily on worker bees. However, this research shifts the focus to the queen and how pesticide exposure affects the entire hive. Angela Encerrado-Manriquez, the lead author and a recent Ph.D. graduate from UC Davis, stated, “In our study, pesticides began to accumulate in queens over time, suggesting that worker filtration capacity can be overwhelmed.”

This accumulation can lead to a slow decline in colony health, potentially contributing to delayed colony collapse. Beekeepers and agricultural planners need to consider these findings when assessing pesticide exposure during foraging or colony expansion periods.

Research Methodology and Findings

The research team created “nanocolonies,” small environments that replicate the dynamics of a typical honeybee hive. Each nanocolony contained one queen and 60 worker bees, and the bees were given food tainted with the pesticide methyl parathion, which was tracked using a radioactive marker.

• Initially, worker bees filtered out 95% of the pesticide.
• By Day 10, this number decreased to 86%, indicating a decline in their ability to remove contaminants.

This collaborative research involved the USDA's Agricultural Research Service and Lawrence Livermore National Laboratory, which provided advanced techniques for measuring pesticide levels. Bruce Buchholz, an LLNL scientist, emphasized the importance of their methods, stating, “With BioAMS, we can trace very low levels of a pesticide.”

Given that honeybee queens can lay between 1,500 and 2,000 eggs daily, understanding the effects of pesticide exposure on their health is crucial for maintaining global food security, as honeybees pollinate about one-third of the world’s food crops.