Expert Voices

Honeybee Collapse May Have Complex Cause (Op-Ed)

A bee lands on a yellow flower.
The cause of colony collapse disorder may be more complex than thought. (Image credit: Bee photo via Shutterstock)

Jeff Nesbit was the director of public affairs for two prominent federal science agencies. This article was adapted from one that first appeared in U.S. News & World Report. Nesbit contributed the article to LiveScience's Expert Voices: Op-Ed & Insights.

Scientists have been trying to discover why millions of beehives have collapsed and died during the past six years. According to a new study, the reason for the phenomenon — known as colony collapse disorder (CCD) — may be much more complex and disconcerting than researchers originally realized.

CCD has killed off more than 10 million beehives in North America since 2007 alone. Scientists have tried repeatedly to identify the root cause for the beehive collapses — with possibilities ranging from certain classes of pesticides to parasites or nutrition — though the search is complicated by the dozens of different chemical types that may be combining to contaminate the pollen bees collect for their hives.

So academic researchers from the University of Maryland and federal scientists from the Department of Agriculture decided to collect pollen from seven major types of crops along the East Coast where CCD has been especially destructive — where bees had been in serious decline — and fed the pollen to healthy bees .

The collected pollen contained an average of nine types of pesticides and fungicides —one pollen sample contained 21 different anthropogenic chemicals.

According to the study, which appeared in the open-access journal PLOS One, the researchers discovered healthy bees that ate the fungicides — which are supposedly harmless to bees — were actually three times more likely to become infected with a parasite that's known to cause CCD than bees not exposed to the chemicals.

The study also indicated that there may not be a single cause of the collapse of bee colonies in North America — the deaths may result from the impact of a complex web of chemicals spanning different types and classes of pesticides and fungicides.

Fungicides are used to control things like fungus on apples, and weren't expected to have an impact on healthy bees. Since the study has shown that bees eating such fungicides are much more likely to become infected with a deadly parasite, USDA may need to change the way it regulates the use of those chemicals around crops and the bee colonies that pollinate them — and the agency may need to change the way it advises farmers and beekeepers about the fungicides' risks.

Likewise, if CCD is linked to other components of the complex array of anthropogenic chemicals in pollen, it will become even more difficult to protect bee colonies — not to mention the other forms of life subjected to those chemicals as they spread through the food web and the broader environment.

To make things even more complicated, in the recent study, the researchers found that healthy bees they sampled had mostly foraged from weeds and wildflowers — not crops — meaning that bees across North America are likely much more exposed to pesticides than previously thought.

More research is needed about "how honey bees are exposed to pesticides outside the field in which they are placed," the authors wrote in PLOS One. "We detected 35 different pesticides in the sample pollen, and found high fungicide loads," they added. "Our results highlight a need for research on sub-lethal effects of fungicides and other chemicals that bees in an agricultural setting are exposed to."

CCD isn't just about the bees — food crops and agriculture economies are affected too. Because bee populations are so low in the United States, for example, the surviving colonies are working overtime to pollinate crops in California and elsewhere. More than $30 billion worth of crops in the United States could be seriously at risk if the continuing die-off of honeybees were to reach critical levels .

While the researchers were careful not to directly link the complex web of pesticides found in the pollen samples directly to colony collapse disorder, the inference is hard to ignore.

It's also just common sense. Something has been causing CCD in different parts of North America, and it would make sense that chemicals designed to kill certain things like pests or weeds might also have unintended consequences when combined and later spread outside crops.

The solution could be as simple as labeling the harmful fungicides. But, it could also be vastly more complicated, and involve tighter regulation of the regions and instances where different sets of chemicals are used in and around crops pollinated by honeybee colonies.

Right now, pesticide labels tell farmers not to spray when bees are known to be pollinating, but those regulations don't apply to the chemicals used to kill fungus on the crops as those substances were thought to be harmless to bees.

But, there is one finding from the study that beekeepers should consider right away: simply looking at the types of chemicals used on crops may simply not be enough.

"Our results show that beekeepers need to consider not only pesticide regimens of the fields in which they are placing their bees, but also spray programs near those fields that may contribute to pesticide drift onto weeds," the authors wrote. "The bees in our study collected pollen from diverse sources, often failing to collect any pollen from the target crop."

The study also points out what we don't know, and need to study more closely. "Given the diverse routes of exposure to pesticides we show, and increasing evidence that pesticide blends harm bees," the authors wrote, "there is a pressing need for further research on the mechanisms underlying pesticide-pesticide and pesticide-disease synergistic effects on honey bee health."

A version of this column appeared as Bee Colony Collapses Are More Complex Than We Thought on the blog At the Edge by Jeff Nesbit on U.S. News & World Report. His most recent Op-Ed was titled Can You Calculate the Impact of Cheating in Sports?. The views expressed are those of the author and do not necessarily reflect the views of the publisher.