The Still Mysterious Case of Missing Bees

Honey Bee (genus Apis) foraging in the field. Photo by Mark Shepherd
Honey Bee (genus Apis) foraging in the field. Photo by Mark Shepherd

We are just four months shy of the 10-year anniversary when David Hackenberg reported losing two-thirds of his bee hives to a phenomenon now known as Colony Collapse Disorder (CCD).   It was in October of 2006 that Mr Hackenberg, a Pennsylvania bee keeper, noticed that 2000 bee colonies he had transferred to Florida to pollinate crops were devoid of almost all adult bees, except the queen.   Like a scene out of a science fiction movie there were no bodies left to explain what happened.  All of the adult bees took flight from the hive never to return, leaving combs filled with honey and larvae.  In January of 2016, Maryam Henein published a story online noting that David Hackenberg had again lost a large number of bee hives.  This time 90 percent of his colonies.   Mr. Hackenberg was not alone in his losses, with other bee keepers reporting large colony losses.  He is now a part of a civil lawsuit filed against the United States Environmental Protection Agency alleging that the ongoing sale and use of neonicotinoid pesticides have caused rapid honey bee kills with long-term effects leading to bee colony mortality, bird mortality, nationwide water and soil contamination, and other environmental and economic harms.  Other researchers, however, question the role  that neonics, as neonicotinoids are often called in the bee keeper industry, play in CCD.

Neonicotinoids are a group of insecticides used on a variety of crops, such as apples, pears, peaches, walnuts, cucumbers and many others.  The most widely used neonicotinoid is imidacloprid. Mimicking the molecular structure of nicotine that is found in a variety of plants such as tobacco, and that can act as a natural defense against insects, neonics over-stimulate insect nerve cells. The over-stimulation results in the noticeable twitching of insects that are fatally poisoned.

In 2012, researchers led by Chensheng Lu of Harvard University  published a paper indicating that exposing bee hives to  imidacloprid led to the death of colonies in significantly higher numbers than hives not exposed to the insecticide.   In the study, however,  dead bees were found on  the ground near the hives, something not seen in colonies affected by CCD.  Hives affected by CCD were reported to be  empty with few, if any, dead bees found.  The researchers explained that the reason they found dead bees was that their study was conducted in winter conditions, where snow on the ground made finding dead bees easier.  In warmer latitudes, sick bees could fly farther and the bodies might not be found.  So it seemed that the mystery might have finally been solved, right?  Well, no.

In March 2013, the FDA published the results of  a 3-year study indicating that while imidacloprid could cause effects on bee health and colony success, effects were not seen at doses typically encountered in the field.  The FDA report stated that even at some high doses imidacloprid,

“had no significant effects on foraging activity or other colony performance indicators during and shortly after exposure…. Given the weight of evidence, chronic exposure to imidacloprid at the higher range of field doses (20 to 100 μg/kg) in pollen of certain treated crops could cause negative impacts on honey bee colony health and reduced overwintering success, but the most likely encountered high range of field doses relevant for seed-treated crops (5 μg/kg) had negligible effects on colony health and are unlikely a sole cause of colony declines”.  

honey bee on flower (apis melifera) photo by mark shepherd
honey bee on flower (apis melifera)

Further, the FDA and Mary Berenbaum, previously at the National Academy of Sciences, noted that Chensheng Lu, “never tested for the presence of pathogens, so his conclusions dismissing other likely causes don’t follow from his data“.  The FDA also noted that with bee populations in 2015 at a 20-year high, the CCD phenomenon identified in 2006 was likely a cyclical  phenomenon that has occurred several times over the last century,  making CCD less of a concern.  Or does it?  Bear in mind that many of the honey bee populations are started with queens that share a very similar genetic makeup, and thus, are potentially susceptible to similar diseases.  If a virus, bacterium, or mite was the real culprit behind CCD,   having some many queens and colonies with such a similar genetic make up could mean another event like the 2006 CCD phenomenon could have a potentially devastating effect.

The general molecular structure of Imidacloprid, a neonicotinoid insecticide suspected of causing colony collapse disorder.
The general molecular structure of imidacloprid, a neonicotinoid insecticide suspected of causing colony collapse disorder.

For more information see the links below

USDA study concludes neonics not driving bee deaths—As White House set to announce pollinator revival plan’





About Mark Shepherd

I work in the environmental movement helping to protect the air we breathe, the water we drink, the land that sustains us and the natural and biological resources we depend on.

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