I seemed to remember them exploiting whatever made the Aliens growth so virulent in the Gibson screenplay, by dismissing the egg and using spores. That is probably another reason why I never was impressed with Prometheus............because I'd read that idea already in the universe a decade before its release in those scripts. The origin is different, but the idea is the same.
I got about a third of the way through the Alien 3 Gibson novelization, maybe its time to finish it.