The ideal time to introduce ladybirds is when aphid colonies are developing. You can, of course, introduce them when there are many more aphids, but then it will take longer and you’ll inevitably need to introduce many more. Now, you should never, ever introduce them when there are no aphids, because at that point, either the larvae will inevitably die (no food), or the adults will leave because there are no aphids to encourage egg-laying.
Videos
Choosing ladybirds: larvae or adults?
Generally speaking, it’s best to introduce ladybird larvae because they are very effective, voracious, and will thoroughly clean the plants....
