Ottawa gardener employs tiny helpers to save prized flowers from pesky beetle

With the help of a Carleton University researcher, an Ottawa gardener has unleashed a foreign parasite in his backyard in hopes of eradicating an unwanted pest that's devouring his beloved lilies.

For years, the red lily beetle has been chewing holes through the leaves and pink flowers of Rob Stuart's Asiatic and oriental lilies. It's a cycle that's taken a toll on his garden.

"It's a two-step process," said Stuart, in his Barrhaven back yard. "The beetles themselves eat the leaves, but the worst offenders are the larvae that hatch from the eggs that they lay on the underside of the leaves. And these are very voracious."

Despite Stuart's attempts at various control techniques over the years, including botanical insecticides, the bugs continued to ravage his lilies. Then, at a meeting of the Master Gardeners of Ottawa-Carleton last fall, he learned of a biological control for the red lily beetles: using parasitic wasps to attack the larvae.

Tiny wasps lay eggs in beetle larvae

Stuart reached out to Naomi Cappuccino, an associate biology professor at Carleton University, who introduced him to Tetrastichus setifer, a tiny wasp native to Europe that's a natural enemy of the red lily beetle.

"Predators tend to avoid the (beetle) larvae, which cover themselves in their own excrement, but there are several species of parasitic wasps that lay their eggs in the larvae," said Cappuccino in an email. "The eggs hatch into wasp larvae that devour the beetle larvae from the inside out."

Last month, Stuart and Cappuccino opened a shot glass-sized container and released about 50 of the wasps into Stuart's garden. He admits it was a daunting notion at first, but at roughly the size of a dot on a page, the tiny insects don't sting people.

"My wife was all worried when she heard that I was getting these wasps into the backyard," he said. "But no, they're so little that I don't think they could penetrate the skin if they had to."

90 per cent effective in test gardens

Because the beetles already did most of their damage by the time the wasps were released, he won't know until next summer how effective they'll be in controlling the pests.

But Cappuccino says similar studies in the United States show the wasps are working. "The wasps are proving to be an effective control method," she added. "In the Boston area, gardeners are no longer complaining about lily beetles."

In Cappuccino's test gardens here in Ottawa, up to 90 percent of the beetle larvae have been parasitized by the wasp.

Stuart is encouraged by those results. "I'm hoping that with the release here that over a couple of years that it'll be much more easy to grow lilies and we won't be faced with the problems that we're faced with now," he said. 

"Because a lot of people have given up growing them, just because they're too much of a hassle."