I am going to assert that the fear of unfriendly AI over the threats you mention is a product of the same cognitive bias which makes us more fascinated by evil dictators and fictional dark lords than more mundane villains. The quality of "evil mind" is what really frightens us, not the impersonal swarm of "mindless" nanobots, viruses or locusts. However, since this quality of "mind," which encapsulates such qualities as "consciousness" and "volition," is so poorly understood by science and so totally undemonstrated by our technology, I would further assert that unfriendly AI is pure science fiction which should be far down the list of our concerns compared to more clear and present dangers.