Release lady beetles at dusk or early evening. Lady beetles will fly away almost immediately if released during the heat of the day or where the sun is shining, so wait until evening to release them. Spray a fine mist of water on the plants before the release. Giving beetles a drink may keep them around longer. Place beetles at the base of plants or in the crotches of low branches. Lady beetles will crawl higher into the plant in search of aphids. Once lady beetles begin to fly, they are likely to fly a substantial distance, often outside the boundaries of your garden. Do not release lady beetles on plants that have been sprayed with insecticides as residues from most insecticides are likely to kill the beetles. However, insecticidal soaps and oils, once dry, will not leave toxic residues.

They need a good supply of aphids. There is no point in releasing them on plants with few aphids. Lady beetles are voracious aphid feeders and an adult beetle will eat 50 or more aphids a day. The convergent lady beetle, which is the species sold for release, feeds almost entirely on aphids and will not remain on plants with low aphid populations and will not control other garden pests.

Expect lady beetles to fly away in a few days. Even when released with care, lady beetles will fly away within a few days. Lady beetles are unlikely to lay eggs on the plants they are released on. If aphids return a week or two later, gardeners will need to release more lady beetles to help increase the local population.
Derived from: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13933