Do Store-Bought Ladybugs Work?

Mostly, no. The ladybugs sold in bags and tubs are almost always convergent lady beetles collected from wild overwintering sites, and most of them fly away within a day or two of release, whether or not your plants have aphids. University of California research found they can control aphids in a small area if you release very large numbers and handle them carefully, but a typical retail package is not enough, and the beetles leave before they settle in.

Where store-bought ladybugs come from

The convergent lady beetle (Hippodamia convergens) is a native North American species. Each winter, huge numbers gather in dense clusters in the foothills and mountains of California. According to UC IPM, the beetles sold commercially are "field collected from their overwintering sites using portable vacuum devices."

That origin explains most of what goes wrong. The Xerces Society notes that these beetles typically need to migrate before they feed and lay eggs, so they "simply fly away when released."

What the research found

The University of California has studied lady beetle releases for aphid control in some detail. The key findings, from a UC IPM summary for nursery and garden centers:

• About 95% of released beetles in research studies flew away within 48 hours.
• One large, heavily infested rose bush needed two releases of about 1,500 lady beetles each, a week apart, to get adequate control.
• Beetles fly off almost immediately if released in the heat of the day or in sunshine.

UC IPM's natural enemies profile says the same thing another way: "Most will fly away from the release site within 1 or 2 days after they are released even if aphids are plentiful." It recommends about 1,500 beetles per rose shrub, released every one to two weeks for as long as conditions favor aphids.

Extension specialists in greenhouse settings report the same pattern. UConn and UMass Extension describe adult lady beetles as "highly dispersive" and "poor at searching out pests," and suggest releasing them only where aphid hotspots already exist.

So the honest answer is that releases can work, in the sense that a lot of beetles eating a lot of aphids for a day or two will reduce aphids. Each adult can eat around 100 aphids a day, per UC IPM. But the effect is temporary, the numbers needed are large, and you are paying for a control that leaves your garden almost as soon as it arrives. UC IPM's home aphid guidance sums it up as "some temporary control when properly handled, although most will disperse within a few days."

The parasite and disease problem

Because the beetles are wild-collected rather than reared, they arrive with whatever they were carrying in the wild. A study of commercial shipments by Bjørnson (2008) in Biological Control found:

The percentages look small, but the author points out that because beetles are sold in large quantities, thousands of infected beetles can be released at once. UConn and UMass Extension note that the microsporidium "shortens their lifespan and reduces the number of eggs laid," and that these organisms could spread to native lady beetles. Because the beetles are field-collected, no quality control standards exist for them.

There is also the question of what collection does to wild populations. The Xerces Society estimates that "likely many millions of beetles are collected from the Sierra Nevada each year," removing them before they disperse to control pests on their own. That estimate is a back-of-the-envelope calculation based on 1999 prices, not a measured count, so treat it as an order of magnitude.

If you release them anyway

If you already have a bag in the refrigerator, you can improve the odds. From UC IPM:

• Release at dusk or in the early evening, not in heat or sunshine.
• Mist the plants first. Beetles need water and stay longer on moist foliage.
• Place them at the base of infested plants.
• Store them in the refrigerator (never the freezer) until use, without food in the container.
• Do not release onto plants with insecticide residues.
• Control ants, which protect aphids from predators.

Expect most to be gone within a couple of days anyway.

What works better

For aphids on sturdy plants, UC IPM suggests a strong spray of water: most dislodged aphids cannot climb back. It also recommends avoiding heavy nitrogen fertilizer, which favors aphid reproduction, and managing ants.

The longer-term answer is to keep the lady beetles, lacewings, hover flies, and parasitic wasps that already live near you. They arrive on their own when aphids appear, provided you are not killing them with broad-spectrum sprays and there are flowers around for the adults. Aphids killed by parasitic wasps turn into swollen "mummies"; seeing those means natural enemies are already at work. The evidence on flowering habitat is covered in attracting beneficial insects.

If you are managing a greenhouse or enclosed space, the UConn/UMass extension article recommends commercially reared species such as the two-spotted lady beetle (Adalia bipunctata) over wild-collected convergent lady beetles. In an open garden, conservation beats purchase.

Related

This page is part of No-Spray Pest and Disease Management, which covers the broader toolkit: exclusion, sanitation, resistant varieties, and habitat. For another physical control with much better evidence than purchased predators, see row covers for pest control.