Bee health is a complicated story that scientists are still trying to unravel. While there are many opinions and theories, most scientists agree that multiple stressors are involved in colony collapse disorder (CCD), but none include GMO crops. . The Agricultural Research Service – United States Department of Agriculture (ARS-USDA) states, “While a number of potential causes have been championed by a variety of researchers and interest groups, none of them have stood up to detailed scrutiny. Every time a claim is made of finding a "smoking gun," further investigation has not been able to make the leap from a correlation to cause-and-effect. Other times, not even a scientific correlation has been demonstrated in the study claiming to have found "the cause" of CCD. Researchers have concluded that no one factor is the cause of CCD. Most likely, CCD is caused by multiple factors. It is not possible to know at this time if all CCD incidents are due to the same set of factors or if the factors follow the same sequence in every case.”
Some claims have tried to link the use of neonicotinoids to GMOs also. See this link for additional details. One key point is that seed treatments are used by growers to protect all plants, not just GM crops. Even organic growers may use seed treatments.