Scientists from the University of California, Davis (UC Davis), have found evidence that honeybee queens exposed to pesticides can offload some of the contamination onto their eggs to ensure their survival.
The findings are published in the journal Current Biology.
In the study – carried out in collaboration with Lawrence Livermore National Laboratory (LLNL) and the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS) – researchers wanted to learn more about the effects of pesticides on bee colonies. Unlike most previous toxicology research involving honeybees, this one focused on the queen, her ovaries, eggs and the wax.
In a beehive, it’s the worker bees that keep the cogs spinning. Younger workers act as nurses, tending and feeding the queen, and providing the larvae with processed pollen and nectar.
Older workers take care of riskier tasks such as foraging for resources, and often end up exposed to chemicals, including pesticides. These chemicals can be transported back to the colony and very easily spread. Despite this, studies have shown that honeybee colonies are more resilient to pesticide exposure than individual insects.
Scientists have long thought that the worker bees help shield queens from contamination by essentially filtering the harmful substances out of the food they pass on. But, according to the new findings, this protection may have its limits.
“In our study, pesticides began to accumulate in queens over time, suggesting that worker filtration capacity can be overwhelmed,” said Angela Encerrado-Manriquez, the paper’s lead author and a recent Ph.D. graduate from UC Davis.
“When his happens, queens have their own defence. Maternal offloading allows them to shunt the toxic burden to their eggs.”
Studying the hive
To get a closer look at this process, the researchers built 'nano-colonies' designed to reproduce key functions inside a hive. Each nano-colony held one queen and 60 worker bees.
The bees were given pollen, water and food, all contaminated with the pesticide methyl parathion, which was tagged with a low-level radioactive marker so researchers could track its movement.
To detect these radioactive markers, a technology called biological accelerator mass spectrometry (BioAMS) was used.
“With BioAMS, we can trace very low levels of a pesticide,” said Bruce Buchholz, an LLNL scientist and co-author of the paper. “The pesticide concentrations we used were not lethal and were environmentally relevant to that seen in nature.”
The findings surprised the researchers. On the first day of the experiment, worker bees filtered out 95 per cent of the pesticide and transferred it into the honeycomb. But by day 10, that dropped to 86 per cent.
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The implications
These results suggest that pesticides may continue to accumulate in a colony after exposure begins, particularly once worker bees reach the tipping point and can no longer filter the contaminants as effectively.
The implications are wide-reaching – for beekeepers, growers and pest-management planners. Honeybees pollinate about one-third of the world’s food crops, so colony losses are a major concern for agricultural productivity and food security.
“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 Sascha Nicklisch, the paper’s senior author and an associate professor in the Department of Environmental Toxicology. “There may be a slow creeping effect of chemical accumulation that will contribute to delayed colony collapse.”
“The queen is the only member of the hive who can lay eggs that become the next generation of workers,” Nicklisch added. “She keeps the colony alive, so understanding how pesticides can affect queen bees and also her offspring is important.”
Future research is needed to determine exactly how long queens can go on transferring contaminants into their eggs and what the long-term consequences may be for the colony.
Read the full findings here.
Top image credit: Megan Kobe/Getty Images
