Females make a large part of mealybug populations, and they can't fly, unlike males. This means the main route of transmission is by bringing newly bought, infested plants into the greenhouse or garden. Plants should always be inspected carefully before any money spent and purchased from a trusted source. To be extra safe, you can quarantine plants for a month before joining it with others.
Regular inspection of plants is advised. Indoor plants should be checked frequently, especially when conditions are warm!
Fallen leaves should be collected and disposed of accordingly in case there are eggs or bugs on them.
Sometimes it is just easier to dispose of the plant if the infestation is too heavy.
For lighter infestations, simply pick off mealybugs with some tissue paper.
Heavier infestations may require a disinfectant or insecticide. You can make one from scratch using water, oil, bio-friendly washing up soap and some chilli or garlic.
Another option would be to use some rubbing alcohol.
Unfortunately, the latter won't get rid of the tiny nymphs and eggs, so reapplication is necessary.
Insecticidal soaps may be applied if infestations don't clear up within a few weeks.
The ladybird Cryptolaemus montrouzieri offers a solid form of biocontrol for glasshouses. Their larvae look a lot like mealybugs, so don't be alarmed if there seems to be more at first! Chemicals should not be used in conjunction with chemical sprays.