Which of the following is NOT a possible cause of bee decline?

Global warming, while a significant environmental issue, is not typically identified as a direct cause of bee decline compared to the other options presented. The primary factors affecting bees include pesticides, which can disrupt their foraging behavior and health; viruses that can infect and weaken bee populations; and mites, particularly Varroa destructor, which are parasitic pests that feed on bees and transmit diseases. These direct threats lead to declines in bee populations and their overall health. Global warming does have broader ecological impacts, such as altering habitats and food availability, but it does not act as an immediate and specific cause of bee decline in the same way that the other factors do.