Unraveling the Honeybee Collapse : Another Thread of Evidence
by Bill Chameides | September 2nd, 2009
posted by Erica Rowell (Editor)
The disappearance of honeybees is cause for concern: the creatures pollinate many of our crops. A new paper offers up new insight into the colony collapse. (Photo: Erik Hooymans, WikiCommons)
Why are honeybee colonies disappearing? A recent genomic study delivers new insights.
Since 2006, about a quarter of U.S. honeybee colonies have vanished each year from causes unknown. Left hanging in the balance is not just the natural sweetener called honey but our agricultural yields — American honeybees pollinate some 90 different crops that bring in more than $15 billion annually.
During the winter of 2006-2007 when bees started to go missing, about 23 percent of colonies nationwide collapsed, with some states losing 50 to 90 percent of them. Unfortunately there weren’t any easy answers for the disappearance. Eventually dubbed Colony Collapse Disorder, or CCD, the plague is characterized by the sudden, complete absence of adult honeybees in a colony — no bodies, nothing, just an abandoned colony sort of like a ghost town of the American West.
The second winter to witness CCD saw an estimated 36 percent collapse of honeybee populations. Bees appear to have had a reprieve this past winter: preliminary data estimate colonies suffering from CCD losses at about 15 percent (though total losses from all causes remain unsustainably high at about 29 percent).
What Might Be Behind the Vanishing Bees
While the culprit responsible for the disorder has yet to be found, there’s been no shortage of theories. Among them are the following:
- parasites (e.g., varroa mites, honeybee tracheal mites),
- pathogens (e.g., viruses, bacteria and fungus),
- pesticide exposure,
- inadequate diet,
- stress from long-distance transportation ,
- use of antibiotics,
- global warming, and
- electromagnetic radiation.
A new paper by Reed Johnson of the University of Illinois at Urbana-Champaign and colleagues published in the Proceedings of the National Academy of Sciences offers up the latest explanation, one that appears to have a good chance of being on the right track.
New Theory Sees Ribosomal RNA As Playing a Role in Missing Bees
Johnson and colleagues’ plausible theory for the sudden onset of CCD does not involve a silver bullet behind the vanishing adult bees but rather a complicated interplay between contributing factors.
The researchers observed that bees with CCD displayed some odd molecular features, including:
- anomalously large amounts of fragmented ribosomal RNA (rRNA), material critical to the production of proteins in cells, and
- a greater likelihood of infections from pathogens that attack normal ribosomal function.
Ribosomes are the factories within the cells of living organisms that take nucleic acid polymers and turn them into amino acids. Ribosomal RNA plays a critical role in this process as an encoder for producing all the different types of proteins needed by the cell, including those critical to fighting pathogens and dealing with more typical stresses such as changes in temperature or nutrition.
Inability to Make New Proteins May Be Important Factor
Johnson et al. hypothesize that the higher concentration of fragmented, broken rRNA in CCD bees may be an intermediate indicator of ribosomal malfunction — an early sign that a bee’s ribosome factories are losing their ability to make new proteins.
This theory is consistent with the second molecular feature the authors noted: that bees with CCD and fragmented rRNA also had a greater likelihood of infections from pathogens that attack normal ribosomal function. These pathogens (for you die-hard virologists, picorna-like viruses that damage ribosomes are among them) co-opt the ribosome factories to make their own viral proteins. Once a bee’s ribosomal function is compromised, it makes less protein, limiting the creature’s ability to cope with pathogens, poor diet, parasites, and other stresses.
Johnson’s team theorizes that there may be a tipping point for the onset of CCD — one that is triggered when normal ribosomal cell function is compromised beyond a certain point. Once reached, CCD-infected bees, no longer able to cope with everyday stresses like pesticide exposure, parasites, and such, would die, starting a downward spiral that would eventually wipe out the entire colony.
Another Piece in the Puzzle, but the Full Mystery Yet to Be Resolved
- Is there a causal link between pathogens that disable normal ribosome function and CCD? This is an important issue since it turns out that healthy bees also have detectable levels of fragmented rRNA.
- Why did the CCD phenomenon appear out of nowhere in 2006? Did the disorder mark the appearance of a new ribosomal-function-attacking pathogen, and if so, what gave rise to this new pathogen? Was it inadvertently imported to the United States, or did it evolve from another pathogen? Perhaps it was the former in the form of the varroa mite, a carrier of picorna-like viruses that was accidentally introduced to America in 1986. But if in 1986, why did the phenomenon not appear for 20 years?
- If CCD is the result of the death of individual bees unable to cope with disease and environmental stress factors, where did all the dead bodies go?
If ribosomal impairment is the smoking gun for CCD,
this study offers a promising avenue for future research to unravel the mystery of our disappearing honey bees. But clearly a lot of unanswered questions remain. More research is the key.
Olivia Judson, “A Low-Tech Treatment for Bee Plague,” New York Times, January 27, 2009.
“Silence of the Bees,” PBS’s Nature.filed under: agriculture, animals, faculty
and: Colony Collapse Disorder, crops, honeybees, pollination, RNA, viruses