Colony Collapse Disorder: The pieces are starting to fit together

I have written repeatedly over the years about the sudden and rapid decline of bee populations, a situation that puts at risk approximately 30% of the crops humans depend on. Over the years many hypotheses have been put forward, no single one of which has managed to explain the decline. Also, the decline has had at least two phases. The earlier one was at least in part due to mite infestations. But the second phase, which continues to this day, has been called Colony Collapse Disorder, CCD, because of the way that a previously healthy seeming colony of bees will suddenly, almost overnight disappear nearly completely leaving behind nothing but a handful of survivors. This thing has had bee keepers and the industries that depend on them (e.g. the almond growers) pretty spooked.

Recently there was a partial breakthrough where a particular fungus was demonstrated to be one major factor in CCD. Infect a colony with the fungus, you get CCD. Cure an infected hive of the fungus and you save it from CCD. But even with that excellent piece of work, there was still controversy over whether there were other major factors. From BBC News:

US researchers claim to have identified a new potential cause for Colony Collapse Disorder (CCD) in honeybees.

The disease is responsible for wiping out many beekeepers' entire colonies over the past few years.

Scientists from the US Department of Agriculture say the pathogens to blame are a fungus and a family of viruses...

When beekeepers sounded the alarm in 2007, scientists started looking for a cause of the mysterious disease...

After having screened the samples, the researchers found that there was a higher presence of a fungus Nosema cerenae in infected colonies.

But it was only recently that they were able to determine that it's when bees are infected both with Nosema and with a group of RNA viruses that it is likely to lead to a collapse of a colony, said Evans...

The article continues by discussing some skepticism among some bee keepers and some alternate hypotheses.

Mites and viruses and fungi, oh my! The three pathogens together are probably largely to blame for the declines both before and after CCD. CCD is what happens when two of the spreading infections interact.

I personally think that a lack of genetic diversity among domestic bees contributes to the susceptibility of hives to disease in general, and the hives have just been hit with two or three simultaneous diseases. Greater genetic diversity wouldn't prevent these kinds of occurrence, but it would limit it. Whether pesticides also contribute remains controversial. Some claim that the susceptibility of the bees to these diseases is due to their immune system being harmed by pesticide use. As far as I have yet seen there has not been strong evidence for this, but it remains a possibility. Claims of "organic" bees being raised without decline also have been exaggerated from what I can tell, particularly since the wide distribution of bees from a hive while foraging makes it nearly impossible to be sure whether those bees have fed from plants treated with pesticides or not. But keep in mind that CCD remains a pretty new phenomenon and one that hasn't been studied as thoroughly as one might wish. So pieces keep being added to the puzzle, and I think we now have some sense of the whole picture, but there may well be pieces still missing.

For more information on CCD please visit the website of the MAAREC Task Force, and Pollinator Partnership. Beekeepers can also help track the problem by participating in a beekeeper survey.