What causes CCD?
The "cause" of CCD is under investigation. To be sure, the hysteria
surrounding CCD has outpaced the science. Beekeepers and investigators have
suggested varroa, inadequate rainfall, proximity to power lines, colony
treatments, moving stresses, genetically modified crops, lack of genetic
diversity, inadequate nutrition and chemicals present in the environment,
just to name a few, as possible causes of CCD. At this point, almost every
conceivable and realistic cause remains a possibility. The leading
candidates and a brief explanation of their potential role are listed below.
1. Traditional bee pests and diseases (including American foulbrood,
European foulbrood, chalkbrood, nosema, small hive beetles, and tracheal
mites): These bee maladies likely are not responsible for CCD because
they do not have a history of causing CCD-like symptoms. That said,
traditional bee pests and diseases may exacerbate CCD. With that in mind,
scientists have not abandoned experiments investigating these candidates.
2. Style of feeding bees and type of bee food: The style of feeding
bees and types of bee food used to feed bees vary considerably among
beekeepers reporting CCD losses. As such, no correlation has been found
between what colonies were fed and their likelihood of survival. Despite
this lack of evidence, many beekeepers have abandoned the practice of
feeding high fructose corn syrup to bees due to indications that it can form
byproducts that are harmful to bees.
3. How the bees were managed: Management style is a broad category
but it can include the type of income pursued with bees (honey production,
pollination services, etc.) or what routine colony management beekeepers
perform (splitting hives, swarm control, chemical use, etc.). As you can
imagine, both of these vary considerably among beekeepers so this possible
cause of CCD is given less attention. That said, poor management can make
any colony malady worse.
4. Queen source: Initial investigations considering queen source as
a cause of CCD have turned up no evidence that the disorder is tied to queen
production. Yet, scientists are investigating the lack of genetic diversity
and lineage of bees, both related to queen quality, as possible causes of
CCD. Regarding the former, it has been said that fewer than 500 breeder
queens produce the millions of queen bees (and therefore all bees) used
throughout the U.S. Geneticists refer to this as a genetic bottle
neck. This lack of genetic biodiversity has, in effect, made U.S.
honey bees a virtual monoculture. Monocultures usually are susceptible to
any pest/disease that invades the system. Honey bees are no exception.
5. Chemical use in bee colonies: Without doubt, the beekeeping
industry is overly-dependent on chemical pesticides and antibiotics used to
treat various bee-related maladies. Overuse and misuse of these chemicals
(including insecticides, vitamins, snake oils, etc.) is rampant. In many
cases, the pesticides used to control varroa
mite<
http://creatures.ifas.ufl.edu/misc/bees/varroa_mite.htm >and small
hive beetles<
http://creatures.ifas.ufl.edu/misc/bees/small_hive_beetle.htm>(just
to name two examples) double as insecticides in other pest management
schemes. Putting insecticides into insect colonies cannot be beneficial to
bees, even if the chemicals are not killing the bees outright. A number of
newly-discovered, sub-lethal effects of these chemicals on honey bees
(workers, queens, and drones) should be given stronger consideration as
possible causes of CCD.
6. Chemical toxins in the environment: A popular theory is that
chemical toxins in the environment are responsible for CCD. In many
instances, the beekeepers reporting colony losses manage large migratory
beekeeping operations. In migratory operations, beekeepers move bees from
blooming crop to blooming crop around the country. Because pesticides are
used widely in cropping systems in an effort to kill herbivorous insects,
one is left to consider the potential for non-target chemical effects on
bees. In addition to being exposed to chemicals while foraging on our
nation's crops, honey bees also may acquire chemicals through contaminated
water sources as they drink water containing chemical runoff. Conceivably,
these chemical residues can accumulate in wax and food stores in the colony,
thus killing bees.
7. Genetically modified crops: A number of people have blamed
genetically modified crops for the widespread bee deaths. Scientists have
begun initial investigations into this theory but all available data suggest
that genetically modified crops are not the culprit, at least as far as the
plants themselves are concerned. Interestingly, many seeds from which
genetically modified crops are grown are dipped first in systemic
insecticides that later appear in the plants' nectar and pollen. This makes
genetically modified plants suspect because of their chemical treatment
history, not because they are genetically modified.
8. Varroa mites and associated pathogens: Even with the hysteria
surrounding CCD, varroa
mite<
http://creatures.ifas.ufl.edu/misc/bees/varroa_mite.htm >remains
the world's most prolific honey bee killers. Not surprisingly,
varroa and the viruses they transmit have been considered as possible causes
of CCD. The primary flaw with this theory is that varroa have been in the
U.S. only since 1987. Therefore, it is impossible for varroa to have
caused the CCD-like outbreaks that occurred prior to 1987. A final point
worth considering in the varroa/CCD issue is that many of the chemicals used
in bee colonies are used to control varroa. So varroa (perhaps not directly)
has been considered a leading candidate because the mite itself is damaging,
it transmits viruses to bees, and it elicits an all-out chemical assault
from beekeepers.
9. Nutritional fitness: Scientists have proposed nutritional fitness
of adult bees as a potential cause of CCD. This topic is being investigated
although little information exists currently to suggest nutrition is playing
a role. Malnutrition is a stress to bees, possibly weakening the bees'
immune system. This could have devastating effects on the bees' ability to
fight pests and diseases.
10. *Undiscovered/new pests and diseases: Finally, undiscovered or
unidentified pests/pathogens are considered a possible cause of CCD. Many of
the known bee pests and diseases in the U.S. were introduced in the
last 30 years. We can expect this trend to continue as globalization
increases. This is already happening. For example, *Nosema apis* (a
protozoa that lives in the digestive tract of honey bees) has been present
in the U.S. for many years. In 2006, scientists discovered and
identified a new nosema species, *Nosema ceranae*, present in some
colonies displaying symptoms of CCD (it also has been found in bee samples
dating back to 1995). When this disease is present in bees in elevated
levels, the bees wander from colonies, never to return. Although many do not
consider *N. ceranae* to be the cause of CCD, it and other new
pathogens may play an important role in elevated bee deaths.
Many scientists believe that CCD is caused by a combination of the factors
above. To illustrate this point, some dead bees showing symptoms of CCD have
had high numbers of normally-benign pathogens in their bodies. The data
suggest a massive immune system crash in infected bees, an event that allows
normally-benign pathogens to kill the bees. In theory, any stress or
combination of stresses (chemicals, genetic bottlenecks, varroa, etc.) can
suppress a bee's immune system. Considering synergistic effects as a
potential cause of CCD makes the disorder increasingly harder to study, but
for now, this conclusion seems to be the safest assumption.
I posted this last week. It was from a friend. Can't find the link but this is from my e-mail.
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