I think the idea of alarm pheromone is a good one. However, I'm going to suggest that there may also be other pheromones involved. I know the smell of alarm, and there's also a sweet honey smell that is different. (I have a very developed sense of smell---when I was doing field botany, I would often i.d. plants simply by smelling them.) As I said before, it might be a good idea to check what's going on in your hive, when you get these smells---swarming behavior? Something disturbing the hive? Something else? Jane B.