Both adults and larvae feed primarily on aphids and occasionally on whiteflies. In California, many lady beetle species overwinter in large aggregations in the Sierra Nevada. In the spring, adults fly down from the mountains to coastal and valley areas. Lady beetles are extremely important natural enemies of aphids.
They are also available commercially, and if used in sufficient numbers and properly handled, lady beetles can effectively control aphids in a limited area. Release lady beetles at dusk or early evening onto plants that have been misted so they are slightly wet. Place them at the base of plants on lower branches. They will crawl up looking for aphids. Make sure the plants have not been sprayed with any insecticides. Expect that most of the lady beetles will fly away within a few days; if aphids return, you will have to release more lady beetles.