Honeybee queens push pesticides to eggs to protect themselves over their offspring

Honeybee Queens Push Pesticides to Eggs to Protect Themselves Over Their Offspring

Honeybee queens facing chronic pesticide exposure will absorb contaminants and pass them to their eggs to ensure their own survival. This process, termed maternal offloading, was documented for the first time in research led by the University of California, Davis and published in the journal Current Biology.

The study reveals a critical limit to the protection queens receive from their colony. Historically, it was believed that worker bees served as a primary filter, removing contaminants from the food they provide to the queen. However, researchers found that this social buffering can be overwhelmed.

According to Angela Encerrado-Manriquez, the lead author and a recent UC Davis Ph.D. Graduate, pesticides began to accumulate in queens over time.

"When this happens, queens have their own defense. Maternal offloading allows them to shunt the toxic burden to their eggs,"

Angela Encerrado-Manriquez, lead author, via ucdavis.edu

The "Tipping Point" of Colony Collapse

The research suggests that pesticides may build up within a colony long after the initial exposure, particularly once worker bees can no longer filter the chemicals. This could create a slow creeping effect of chemical accumulation that contributes to delayed colony collapse.

Sascha Nicklisch, an associate professor in the Department of Environmental Toxicology and the paper's senior author, warned that a tipping point occurs when eggs become so loaded with chemicals that they may no longer develop properly.

"In order to protect herself, the queen bee offloads these chemicals into her eggs to get rid of them,"

Sascha Nicklisch, senior author, via ucdavis.edu

Because the queen is the only member of the hive capable of laying eggs that become the next generation of workers, any impact on her offspring threatens the survival of the entire colony. This is particularly significant as honeybees pollinate about one-third of the world's food crops, and losing colonies diminishes food security and agricultural productivity.

Experimental Design and Findings

To observe these behaviors, researchers created nanocolonies using conical plastic containers with netted bottoms, each containing one queen and 60 worker bees. The teams provided the bees with food, water, and pollen tainted with the pesticide methyl parathion, which was tagged with a low-level radioactive marker.

The study utilized a collaboration between the USDA and the Lawrence Livermore National Laboratory (LLNL). LLNL scientists used biological accelerator spectrometry (BioAMS) to trace the pesticide at an atomic level. Bruce Buchholz of LLNL noted that the concentrations used were environmentally relevant to those seen in nature and were not lethal.

The data showed a decline in the workers' ability to protect the queen over time:

• On the first day, worker bees filtered out 95% of the pesticide, depositing it into the honeycomb.
• By day 10, that filtration rate fell to 86%.

Broader Impacts on Reproductive Bees

Separate research published in PLOS ONE examined insect growth disruptors (IGDs) such as pyriproxyfen, methoxyfenozide, and diflubenzuron. This study found that a positive control, novaluron, resulted in deformed larvae hatching from eggs laid by exposed queens. These larvae exhibited a smooth cuticle without segmentation and failed to curl into a normal shape.

Future research will investigate how long queens can continue passing contamination to their offspring, whether the effects vary by the specific type of pesticide used, and the long-term consequences for colony stability.