Ladybug, ladybug, where have you gone?
Experts warn aphid fighters can spread pathogens
To some casual observers, ladybugs (or lady beetles) are colourful symbols of good luck. Gardeners value them for their utility as ravenous insects that prey upon plant pests. They buy them by the hundreds online or from garden centres, and then free them to hunt.
But many entomologists believe that commercially sold ladybugs are inefficient for biological pest control, and introduce diseasecarrying pathogens to their wild counterparts. They also fear that field-gathering the dormant insects by the millions shrinks the population available to farmers, prompting heavier pesticide use.
The Xerces Society for Invertebrate Conservation, a pollinator preservation group in Portland, Ore., doesn’t recommend buying or releasing non-native lady beetles, especially for yards and gardens, said executive director Scott Black.
While it may be cheap to buy a bag or more of ladybugs to patrol residential landscapes, it’s difficult if not impossible to keep these miniature mercenaries from wandering.
Whitney Cranshaw, a professor and extension entomologist with Colorado State University, has released lady beetles into his greenhouse several times to feed on aphid-infested plants, only to report negative results.
“Twenty-four hours later I can find about six in the greenhouse after releasing a bag of 1,500,” Cranshaw said.
Mature ladybugs will feed on 20 to 25 aphids per day, but their latestage larvae will consume 10 times that number, making them far more effective predators, he said.
When improving habitat in your yard or garden, add plants that appeal to beneficial insects as they phase through all of their successive life cycles, Cranshaw said.
Learn how to identify the insects as they mature.
While ladybugs are collected almost exclusively in the wild, most other predatory insects sold commercially are reared in insectaries, Cranshaw said.
“Praying mantises are popular, but I’m not high on them, either,” he said. “They’re generalists and will eat anything out there, including bees and butterflies.”
Cranshaw suggests using green lacewings, predatory midges and parasitic wasps for insect control. Look up “beneficial insectaries” for suppliers.
“Sometimes all you have to do is spray pests like aphids and spider mites off (with water) or use some insecticidal soap,” Black said.