Numerous prior posts have looked at the evidence, pro and con, for various theories and studies of honeybee colony collapse. From stress to food sources to pesticides, the evidence has been less than compelling. One thesis that arose early and still seems to have some validity is the "Israeli acute parasitic virus."
Now, eleven species of wild pollinators in the United States have turned up carrying some of the viruses known to menace domestic honeybees, possibly picked up via flower pollen, according to researchers. Most of these native pollinators have not been previously found to possess honeybee viruses. Researchers expressed concern that domestic and wild pollinators could be swapping viral diseases that could impact both bee populations. Surveys show, for example, that wild bumblebees are dwindling in number, and so viruses may be a factor in the decline.
One of the most interesting results in the study is the detection of deformed-wing virus and sacbrood virus in pollen carried by foraging bees that were not themselves infected. Healthy foraging insects carrying virus-laden pollen are one of the pieces of evidence that researchers use to argue that pollen by itself can transmit viral infections. This raises concerns about possible virus transmission through the 200 tons of honeybee-collected pollen used to feed bumblebees in bee-raising operations worldwide.
The study can be found at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0014357;jsessionid=E7338255216B12A3985AC8C86CF280FC.ambra01.