A joint USDA/EPA report addressing the continuing mass die-offs of honeybees points to a wide range of causes. Those include parasites, disease, genetics, poor nutrition and pesticide exposure.
Last October, experts from around the country gathered to assess the state of the science of honeybee health. The report is “the outcome of that conference,” said Sonny Ramaswamy, director of USDA's National Institute of Food and Agriculture, during a Thursday (May 2) press conference.“In many ways it’s a landmark report … and represents the consensus of the scientific community on the challenges our honeybee populations are facing.”
Read the report here. 
The challenges are complex and, “as in most things biological, there is no smoking gun. The decline in pollinators we’ve observed in recent years is truly due to a whole host of factors. … It is imperative we take action to address the factors contributing to the decline of honeybees and the continuing impacts that our farmers and honey producers are facing.”