How are ladybugs used in organic farming?

As biological controls of plant pests is the use of ladybugs [Coccinellidae family] in organic farming and gardening. That means that they're used instead of artificial, chemical, commercial, conventional, synthetic pesticides. They eat such pests as aphids, mealybugs, mites, and scale insects. But in the process, and unlike many pesticides, they leave no toxic traces.