No one knows yet or even has a decent speculation on Colony Collapse Disorder (CCD).
It has now been reported in England, Europe, and South Africa.
.................
In case anyone is unfamiliar with CCD, here is an excellent overview from Wikipedia (which continues to get better every day it seems):
Colony Collapse Disorder (or CCD) is a poorly understood phenomenon involving the massive die-off of a beehive or bee colony. The BBC has referred to it as VBS (Vanishing Bee Syndrome). It was originally apparently limited to colonies of the Western honey bee in North America,[1] but European beekeepers have recently claimed to be observing a similar phenomenon in Poland and Spain, with initial reports coming in from Switzerland and Germany, albeit to a smaller degree[2]. The cause (or causes) of the syndrome is not yet well understood and even the existence of this disorder remains disputed. Theories include environmental change-related stresses,[3] malnutrition, unknown pathogens (i.e., disease[4]), mites, pesticides such as neonicotinoids, genetically modified (GM) crops[5] or electromagnetic radiation, such as cellular phone signals.[6]
>From 1971 to 2006 approximately half of the U.S. honey
bee colonies have vanished, but this decline includes
the cumulative losses from all factors such as
urbanization, pesticide use, tracheal and Varroa mites
and commercial beekeepers retiring and going out of
business, and has been fairly gradual. Late in the
year 2006 and in early 2007, however, the rate of
attrition was alleged to have reached new proportions,
and the term "Colony Collapse Disorder" was proposed
to describe this sudden rash of disappearances.[1]
Limited occurrences resembling CCD have been documented as early as 1896,[4] and this set of symptoms has in the past several decades been given many different names (disappearing disease, spring dwindle, May disease, autumn collapse, and fall dwindle disease). Most recently, a similar phenomenon in the winter of 2004/2005 occurred, and was attributed to Varroa mites (the "Vampire Mite" scare), though this was never ultimately confirmed. In none of the past appearances of this syndrome has anyone been able to determine its cause(s). Upon recognition that the syndrome does not seem to be seasonally-restricted, and that it may not be a "disease" in the standard sense—that there may not be a specific causative agent—the syndrome was renamed.[7]
[...]
full -
<http://en.wikipedia.org/wiki/Colony_collapse_disorder>
References -
1. <http://www.aginfo.psu.edu/News/07Jan/HoneyBees.htm>
2. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-0>
3. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-cnn>
4. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-CCDWG>
5. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-1>
6. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-cellphone>
7. <http://en.wikipedia.org/wiki/Colony_collapse_disorder#_note-Prelim>
.d.