Unfortunately, nobody knows what causes CCD. There are many suspects, but most if not all have been ruled out as "the" cause. It may be that the search for "the" cause is flawed, in that no single factor causes it, but a combination of many: bee transport, neonicotinoids and other pesticides used in ag, pesticides used by beekeepers themselves, exotic parasites and hive pests, et cetera. Perhaps scariest, as pointed out in this article, is that population decline/collapse among pollinators isn't limited to the artificially maintained populations of honeybees. As to the health of populations of wild pollinators we have only scratched the surface. The one thing that is certain is that a continuing decline in pollinators is ultimately catastrophic.