July 20, 2000
LONGVIEW, Wash. (AP) -- Governmental agencies have started a war in Cowlitz County between a pesky plant and an army of bugs that love to snack on it.
Rhinocyllus conicus, also known as thistle-head weevil, and gall flies have been imported to control Canada thistle, a prickly weed that crowds out native plants.
The southwest Washington county's Public Works Department and Diking District 1 released 19 colonies of weevils and three colonies of gall flies in areas from Toutle to Woodland.
Canada thistle is a big problem for farmers and gardeners, said Monte Brown of the Public Works Department.
Brown said releasing nonnative bugs to eat nonnative plants is a low cost and environmentally friendly alternative to chemicals and mowing. A colony of 100 weevils costs $40.
"You have to go to other avenues," Brown said. "You can't just spray, spray, spray. It's very expensive and labor-intensive to go out and spray."
Opponents, however, are concerned the weevil could find native plants just as tasty as the unwanted thistles.
Peter McEvoy, an Oregon State University professor of ecology and biological control, warned that the insects could spread to other areas.
The Lewis County Noxious Weed Control Board released the weevil in its county a few years ago. The insect hasn't caused problems -- or had much effect on Canada thistle, said weed-control coordinator Bill Wamsley.
The weevil may have already migrated to Cowlitz County from Lewis or Clark counties, where it has also been released. Diking district operations foreman Dan Finn said he found the insect in a field in West Longview before he released colonies of weevils there.
"I would have expected that actually," McEvoy said. "With chemicals, you expect the effects to diminish with distance and time. You can't expect that with biological control."
The Canada thistle originated in the Mediterranean and spread to North America, perhaps as contaminants in crop seeds. Without the insects that controlled its growth in Europe, the thistle spread in Canada and the United States.
The weevil was brought to North America in 1968 to control musk thistle. It also has been used to control plants such as milk thistle and Scotch thistle.
Washington State University entomologist Gary Piper said weevils can target thistles better than less selective chemicals.
"When you spray herbicides, you're not preserving biodiversity, you're destroying biodiversity," he said.
The Rhinocyllus conicus, however, is not universally lauded.
In the mid-1990s, a University of Nebraska botanist, Svata Louda, discovered the weevil destroying the Platte thistle, a native species that provides food for butterflies and bees.
Cowlitz County has imported insects before. In the mid-1970s, it put out thousands of cinnabar moths to control tansy ragwort, a plant deadly to livestock.
