Releasing Lady Beetles to Control Pests
Based on an intern project by Rachel Vecchio, Certified Master Gardener
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Photo © 2017 John Rusk
THE MYTH: It’s a good idea to release lady beetles in the garden in summer to help control pests.
THE REALITY: Despite their adorable appearance and gentle nature, lady beetles are proven voracious eaters, particularly of aphids and mites. The question, though, is whether this appetite justifies releasing lady beetles in the garden to help control those pests and others.
Lady beetles, also known as ladybugs or lady bird beetles, can be purchased at garden centers. The lady beetles, typically convergent lady beetles (Hippodamia convergens), have been collected from mountainous areas of the West Coast where they overwinter. However, there are some problems with this approach. First, lady beetles deteriorate quickly if they are not handled properly after purchase: They must stay hydrated and refrigerated until release. Second, their tendency is to fly away once they’re released.
According to the University of California Division of Agriculture and Natural Resources, 48 percent of released lady beetles fly away within 48 hours with the remainder gone within four to five days. Third, assuming the beetles will stick around long enough to assist with pest control, a significant number are required. One study by the University of California found it necessary to release a total of 3,000 lady beetles to help control pests on just one heavily-infested rose bush. Fourth, studies have shown that field-collected beetles may harbor parasites and pathogens that may be inadvertently released along with the beetles.
Further, to keep lady beetles happy in the garden, one thing is needed: food. Food sources may include pests, primarily aphids and mites, plant pollen and nectar. Once the food is gone, the lady beetles will leave.
This presents a conundrum. Clearly the gardener wants neither a steady source of insects nor to have pollen and nectar fully consumed from a flowering plant. So, there’s no way to provide an ongoing source of food for released lady beetles – even if they stick around in the first place.
The expense of purchasing the significant amount of lady beetles required for pest control and the high probability they will fly away does not justify releasing them for pest control benefits. However, because lady beetles are proven predators, gardeners should consider growing flowering plants that will naturally attract lady beetles, such as caraway, cilantro, cosmos, dill, goldenrod (Solidago species), marigold, milkweed (Asclepias species), tickseed (Coreopsis species) and yarrow (Achillea species).
References
Chalker-Scott,, L., & Bush, M. (n.d.). Lady Beetles: Should We Buy Them For Our Gardens? Retrieved March 02, 2018, from http://extension.wsu.edu/publications/pubs/fs268e/?p-page=1
Convergent lady beetle. (2014, May). Retrieved March 02, 2018, from http://entnemdept.ufl.edu/creatures/BENEFICIAL/convergent_lady_beetle.html
Cranshaw, W. W. (2014, July). Lady Beetles – 5.594. Retrieved March 02, 2018, from http://extension.colostate.edu/topic-areas/insects/lady-beetles-5-594/
Flint, M. L. (2014, May 14). Lady bugs need special care to control aphids in the garden. Retrieved March 02, 2018, from http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13933
Gillman, J., & Maynard, M. (2012). Decoding gardening advice: the science behind the 100 most common recommendations. Portland, Or.: Timber Press.
Gredler, G. (2001, July). Encouraging Beneficial Insects in Your Garden [PDF]. Oregon State University.