In this case the actor isn't the bee but the bee's genetic programming, which only propagates via the queen and hive. If the programming allows a bee to cary a

In this case the actor isn't the bee but the bee's genetic programming, which only propagates via the queen and hive. If the programming allows a bee to cary a fatal disease back to the hive, the program ceases to propagate and may cease to exist. This provides strong selection pressure against fouling the hive.