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It looks like the Aeonium has Mealie Bugs, the white messy part is a waxy coating they make to protect themselves from predators. You can clean them off with a Q-tip or artist brush dipped in alcohol (rubbing or drinking). Then follow up with either Insecticidal Soap or Neem Oil spray. Watch for ants, as they farm Mealie Bugs like dairy cows and carry them around to new plants to “milk” them.