I've only had this happen once or twice, and beetles weren't really involved, but my theory about this is there is a point where there are so few worker bees, that they simply cannot keep up with all the work in the hive, and at that point, they sort of don't know what to do. It's kinda like when you go to clean and organize a really messy room or closet, and you are so overwhelmed by how messy it is that you don't know where to start, so you just keep putting it off. I just think that when there are so many different jobs that need doing, and none of them are getting done, the workers aren't sure which job is most important, so they don't do any of them. Or perhaps they are trying their best, but there is simply not enough bees to make any headway on the tasks, so the hive just slowly dwindles out.