Turning beetles loose on loosestrife
People have taken a pickax to it, set it on fire, and doused it with lethal chemicals. But nothing loosened the grip of purple loosestrife until bug experts brought in the beetles.
Tenacious and aggressive, purple loosestrife is a colorful perennial flower that has become a persistent weed in wetlands along the northern tier of the United States and in Canada. Unchecked by natural organisms that keep it under control in its native Europe, purple loosestrife crowds out native species like cattails and destroys wildlife habitat.
Eight years ago, Gary Piper, a specialist in the biological control of weeds and associate professor of entomology at Washington State University in Pullman, decided to reunite the pesky plant with its natural predators by importing several species of beetles from Germany.
The results were amazing, he says. Hungry leaf-eaters of the Galerucella species flocked to the young plants in spring and chewed on their leaves. The larvae stripped the tissues from the leaves, then moved up the stem and ate the buds and flowers. The result was a completely denuded plant that curled up and died.
"With projects like this you have no way of determining just how many years it will take," says Dr. Piper. "Some projects I've worked on for 20 years with no dramatic reductions. But within just a few years we have seen populations of [purple loosestrife] literally disappear."
Although early results were encouraging, Piper wasn't finished. Like any perennial, purple loosestrife stores its energy in its root system. Every plant also releases a mind-boggling 2-1/2 to 3 million seeds per year. To make sure an area is completely free of the plant, the roots and seeds of purple loosestrife had to be eliminated. So Piper imported an additional species of beetles that specialize in feeding on roots and eating seeds.
"I don't think you should put all your trust in just two insects," he says. "The more you release the better."
Piper says that by releasing 1,000 to 2,000 adult leaf-eating beetles, plus a quantity of root-eating beetles and some seed-eaters, control can often be achieved in three to five years.
People always ask him if, once the weeds are gone, the hungry beetles will become a problem. But, thanks to the inimitable workings of nature, there's little chance of a beetle plague. Take away the food, and the bug population declines, he points out.
Piper has been swamped with calls from people interested in using the beetles. Faced with new regulation of pesticides and a renewed understanding of "safer and saner" solutions, biocontrol of pests is growing in popularity, he says.
"There's more than one way to kill a weed, and this approach that I utilize is becoming more and more accepted." Numerous other states are also experimenting with biological control of purple loosestrife and other persistent weeds.
Buoyed by his success, Piper is also working on finding natural predators for knapweed, which makes range land unusable; yellow starred thistle, which is fatal to horses; Canada thistle; and poison hemlock.
(c) Copyright 2000. The Christian Science Publishing Society