Mail order businesses and some garden centers sell beneficial insects that can be released into a yard or garden, but once released they may not stay around and provide the control needed. For instance, if you buy lady beetles that were collected in the wild during their winter resting phase, they will likely follow their instincts to migrate as soon as you release them in your garden. Often, lady beetles are only a good buy if they are to be released in a greenhouse where they can't escape, or if they were collected during the spring after they had already migrated and are ready to start feeding. If you do purchase insects, there are some ways to encourage them to stay in your garden. Make sure you have the right predator or pathogen for your pest problem.
Some biological controls prey on only one or a few related species.
The timing of the release is important. If released too early, there may not be enough food and they may leave or die. If released too late, there may be too many pests for them to control effectively. Release the helpful insects on infested plants, making sure food is available to them. Mist the plants with water.