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Lady Beetles: Should We Buy Them For Our Gardens?

Lady Beetles: Should We Buy Them For Our Gardens?

FS268E
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Linda Chalker-Scott, Extension Urban Horticulturist and Associate Professor, Washington State University, Mike Bush, Extension Entomologist, Washington State University
Lady beetles are a popular biocontrol method for aphids in home gardens and landscapes. Many gardeners purchase these insects at nurseries, garden centers, and online. This publication discusses the drawbacks to using purchased lady beetles and suggests some alternatives for attracting and retaining local species.
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Overview

Lady beetles are a popular biocontrol method for aphids in home gardens and landscapes. Many gardeners purchase these insects at nurseries, garden centers, and online. This publication will discuss the drawbacks to using purchased lady beetles and suggest some alternatives for attracting and retaining local species.

A Brief History of Harvesting

Every serious gardener regards the lady beetle as a companion-in-arms in the fight against aphids and other garden pests. Best known in the United States is the convergent lady beetle
(Hippodamia convergens Guérin-Méneville; Figure 1), a voracious consumer. As early as 1924, these insects were collected by the thousands from the Sierra Nevada mountain region and released in California’s Imperial Valley for aphid control on commercial crops (Davidson 1924). The results were so impressive that lady beetle harvesting and shipping has become a lucrative biocontrol business (Bjørnson et al. 2011). Adult beetles are collected from their natural habitat, placed under prolonged hibernation, and shipped to farmers and home gardeners alike. Both adult and larval lady beetles (Figure 2) not only control aphids (Figure 3), but they also prey on scale insects, mites, beetle larvae, and immature bugs (Evans 2009).

Problems with Purchased Lady Beetles

Popular literature often recommends the purchase and release of lady beetles such as Hippodamia convergens (Lind 1998). Recently, however, researchers have raised concerns over the unintended ecological consequences of importing insects for biological control (Howarth 1991; Simberloff and Stiling 1996).

Figure 1. The Convergent lady beetle (Hippodamia convergens Guérin-Méneville) is one of the most common lady beetles in North America with a body size of about 1/4-inch long. The converging white lines on the prothorax behind the head are characteristic to this lady beetle species. (Photo credit: Mike Bush, WSU Extension)
Figure 1. The Convergent lady beetle (Hippodamia convergens Guérin-Méneville) is one of the most common lady beetles in North America with a body size of about 1/4-inch long. The converging white lines on the prothorax behind the head are characteristic to this lady beetle species. (Photo credit: Mike Bush, WSU Extension)
Figure 2. Larval (immature) lady beetles are also predatory on soft-bodied insects like aphids. Be sure to recognize and conserve immature lady beetles. (Photo credit: Mike Bush, WSU Extension)
Figure 2. Larval (immature) lady beetles are also predatory on soft-bodied insects like aphids. Be sure to recognize and conserve immature lady beetles. (Photo credit: Mike Bush, WSU Extension)

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