Lady beetles (known more commonly as ladybugs) are often sold in nurseries and garden centers to control aphids. But will releasing them actually solve your pest problem, and if so, how can you release them correctly?
There are about 200 species of lady beetles in California, varying in color, size, and diet. Most are predators of pest insects as both adults and larvae. Some species feed primarily on aphids, while others are specialized to feed on scales, mealybugs, and even fungus! Lady beetles sold commercially in California are convergent lady beetles, Hippodamia convergens. They are named for the converging white lines on their thorax. Suppliers collect the lady beetles from their overwintering sites in California's foothills and mountains to sell in nurseries and garden centers.
Purchased lady beetles will inevitably disperse. In research studies, about 95 percent of released beetles flew away within 48 hours. The remainder were gone within 4 or 5 days. Even so, University of California research has demonstrated that lady beetle releases can effectively control aphids if properly handled and applied in sufficient numbers. For example, aphids on roses can be controlled by releasing 1,500 lady beetles per plant at 1-to 2-week intervals. Each adult can consume about 100 aphids per day before it disperses, and larvae, which cannot fly, can eat up to 500 aphids!
Lady beetles occur naturally, so for small gardens, it may be more effective and less expensive to create an environment that attracts lady beetles rather than purchasing them. You can do this by planting a variety of flowering and nectar-producing plants since adult beetles will feed on pollen and nectar in addition to pest insects. To protect natural enemies like lady beetles, limit use of broad-spectrum insecticides that kill a wide range of insect pests.
If you choose to release purchased lady beetles for aphid control, be sure to follow these tips to improve their effectiveness:
- Keep live lady beetles refrigerated until release. Lady beetles should not be kept at room temperature for too long, in the sun, or extreme heat. If you don’t plan to immediately release the live beetles, store them in the fridge–not the freezer! Note that refrigerated lady beetles can excrete an unpleasant odor so you may not want to store them with food.
- Make sure they stay hydrated. Store bought lady beetles are often dehydrated and need water, especially if they have been kept at room temperature for a few hours. Mist the lady beetles with water before placing them in the refrigerator for storage, making sure not to let water puddle in containers. If releasing them immediately after purchase, mist the plant you are releasing them onto with water.
- Have a good supply of aphids for them to feed on. Lady beetles are less likely to stick around if your garden doesn’t have enough aphids for them to feed on.
- Release in the evening. When you are ready to release live lady beetles, do it in the evening. If you release them during the day, they are more likely to fly away. Releasing them after sunset can encourage them to spend the night in your garden.
To learn more about the species of lady beetles useful in pest control, see the Natural Enemies Gallery. View Pest Notes: Biological Control and Natural Enemies of Invertebrates to learn more about natural enemies or “good bugs”.
[This article was modified from the original version published in the June 2011 issue of the Retail Nursery and Garden Center IPM News.]