Where have all the honeybees gone?
A new study seems to strengthen the evidence
linking pesticides used on crops to colony
collapse disorder in honeybees.
Colony collapse disorder, or CCD, is a
phenomenon in which honeybees inexplicably
disappear from their hives. The bodies of the
dead bees are typically never found.
Researchers led by Chensheng Lu of Harvard
University have pinpointed the collapse of
honeybee colonies on a class of pesticides
known as neoniotinoids — insecticides that also
act as nerve poisons and mimic the effects of
nicotine. Scientists specifically looked at how
low doses of two neoniotinoids — imidacloprid
and clothianidin — affected healthy bee hives
over the course of a winter.
The results of the study "reinforce the conclusion
that sub-lethal exposure to neonicotinoids is
likely the main culprit for the occurrence of CCD,"
the authors wrote in their paper, published May 9
in the Bulletin of Insectology.
Disappearing Bees
Colony collapse disorder was first widely
reported in America in 2006. Since then, a
complex web of factors has been attributed to
the mass honeybee die-offs, including everything
from disease, parasites, and poor nutrition to the
stress of being trucked around the country each
year to pollinate different orchards.
Many scientists have theorized that a
combination of these factors with exposure to
pesticides could be causing the CCD
phenomenon.
In contrast, the new study found that long-term
exposure to small amounts of neonicotinoids
wasn't compromising the bees' immune
resistance to pathogens — the hives had just as
many infections when they weren't exposed to
pesticides. This suggests that "neonicotinoids
are causing some other kind of biological
mechanism in bees that in turn leads to CCD,"
according to a release.
The Experiment
In October 2012, the Harvard team setup 18
hives at three locations in Massachusetts. At
each location, four hives were fed high fructose
corn syrup laced with neoniotinoids and two
were left untouched. Researchers planned to
monitor the hives over the winter since that's
when the die-outs occur.
By the spring of 2013, researchers said half of
the colonies treated with pesticides had
abandoned their hives — the key symptom of
CCD. The ones that were left weren't in good
shape. Their honeybee clusters were very small
and either lacked queen bees or developing bees,
the study noted. Only one of the untreated
colonies was lost, and in that case the bees'
bodies were actually inside their hives and
showed symptoms that appeared to be caused
by a type of parasite.
Bulletin of Insectology
A chart shows the diminishing number of bees in
imidacloprid- and clothianidin-treated colonies
(the red and blue lines, respectively) between
October 2012 and April 2013.
The new study replicates a previous experiment
done by the same group in 2010. In that study,
the team only tested imidacloprid and found a
higher rate of collapse — 94% of pesticide-
treated colonies disappeared. They think the
disparity might be related to a colder winter,
which stresses the bees and exacerbates the
effects of pesticides.
It's still not clear what role neonicotinoids play
in causing the honeybees to leave their hives
during the winter, but the researchers suggest it
could be "impairment of honey bee neurological
functions, specifically memory, cognition, or
behavior."
It's been previously suggested that
neonicotinoids affect the bees' ability to
remember how to get back to their hives. The
bees get lost, which would explain why
beekeepers usually can't locate the dead bodies.
Study Challenges
Some bee researchers have found several things
to gripe about with this study, including the
small sample size, which was also a criticism of
the initial experiment. At IFLScience.com,
entomologist Jake Bova notes that hive
abandonment is not a definitive sign of CCD.
"Honey bees may abandon their hives for any
number of different reasons, and this study
doesn’t control for any of them."
Other critics have taken issue with the delivery
method of the pesticides. In response to the
2012 study, May Berenbaum, head of entomology
at the University of Illinois, noted to The Boston
Globe that there's been "no evidence of
neonicotinoids in commercially available high
fructose corn syrup" and that fact "undermines
the premise of bees being exposed to pesticides
through the food provided by beekeepers."
Further, The Examiner's James Cooper points
out the study was published in an "obscure
Italian journal" with a measly impact factor
of .375 (for comparison, the journal Science, one
of the most reputable in the world, has an
impact factor of 31.027).
Cooper also said the authors "do not account for
the fact the France still observes CCD each year,
even though they banned neonicotinoids 5 years
ago."
Three neonicotinoids are currently banned in the
European Union, but these pesticides are still
widely used in the United States. Most corn
planted in the U.S. is treated with neonicotinoids
— and while bees don't pollinate corn, they are
exposed to the chemical since the corn's pollen
floats to flowers and other crops nearby.
Our World Without Honeybees
Objections to the study seem to belie the fact
that any research on colony collapse disorder
gives much-needed attention to a global crisis
that puts us all at risk. One-third of the food we
eat depends on insect pollination, mostly by
honeybees that are raised and managed by
beekeepers. There is no good replacement for
honeybees, which are easy to manage in masses
and are unmatched in the variety of crops they
can pollinate — everything from apples and
cherries to broccoli, pumpkins, and almonds
depends on honeybees.
Over the last six years, American beekeepers
have lost 30% of their hives each winter on
average.
The Harvard study comes out just before the
United States Department of Agriculture is set to
release its annual report of winter honeybee
losses. In a media alert, the department said that
losses are "expected to be significant due to
several contributing factors, including exposure
to neonicotinoid pesticides."
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