The piece of evidence from the text that is best supported by analysis that human actions are weakening bumblebees' attachment is: a study that shows viruses can spread from commercial hives to wild bees.
This evidence highlights how human activity, such as the keeping of commercial hives, contributes to the spread of viruses that negatively impact wild bumblebee populations. This connection illustrates how human actions are detrimental to the health and survival of these bees.