Scientists research foreign bugs to help kill invasive plants in Midwest

By John Keilman, Chicago Tribune reporter


Across the Midwest, scientists are fighting an invasion of exotic, fast-spreading plants with imported insects that have one simple mission:

Eat and destroy.

It's an old agricultural tactic known as biological control, used here in recent years to dramatically cut down the scourge of purple loosestrife. Researchers are now looking into new bugs to sic on other plants in the rogues' gallery of Illinois vegetation: garlic mustard and buckthorn.

The insects travel and sustain themselves, so they can be a herbicide-free way to stop marauding plants on public and private property alike. For area homeowners it could mean getting control of their yards without putting down gallons of spray.

But the strategy is not without risk. Some alien insects are only moderately effective while others have become nuisances, chewing up flora they were not supposed to eat and spreading far beyond their intended boundaries.

It leaves even some practitioners of biological control uneasy about the potential consequences of unleashing new waves of miniature mercenaries.

"There's always that apprehension: Things are great now, but what will things be like [in the future]?" said Dan Thompson, an ecologist with the DuPage County Forest Preserve District. "Will something we bring in now haunt us down the road?"

Biological control uses an outsider to beat an outsider. When purple loosestrife, a flowering weed native to Europe, began taking over fields and forests in Illinois, officials turned to an insect that loved snacking on the plant back in the old countries.

Galerucella calmariensis, a tiny brown beetle, was released across the Chicago area in the mid-1990s. Its success was dramatic. The purple tide receded where it had crowded out native species, and plants such as wild iris, Joe Pye weed, blue joint grass and turtlehead began to return.

"There were literally thousands and thousands of acres of loosestrife up here 10 years ago," said Ken Klick, a restoration ecologist with the Lake County Forest Preserve. "And though it's still around, you don't see the monocultures you used to. We're very pleased."

The loosestrife campaign led to plans to take on other Midwestern plagues. The next target on the hit list is garlic mustard.

Imported from Western Europe as a delicacy in the 1860s, the piquant herb gradually spread out of control, covering forest floors like a carpet and smothering already established plants.

Within a year, researchers in Minnesota and New York hope to unleash a German weevil that devours garlic mustard from root to leaf. They've been looking at the bug for a decade, plying it with dozens of other plants to learn whether it might eat anything else.

"We want to make sure the only plant that will be attacked is garlic mustard," said Bernd Blossey, who is doing research at Cornell University.

Scientists have also looked for insects to combat teasel, an up-and-coming nuisance that has blanketed Illinois during the last 20 years. They have found contenders among European fleas and butterflies.

But the king of all plant invaders—buckthorn, an aggressively spreading shrub that starves native species of sunlight—might be the most resistant to an insect assault.

David Ragsdale, a professor of entomology at University of Minnesota who is researching buckthorn's insect enemies, said 50 species tested in Europe were rejected because they eat other vegetation. Meanwhile, the five he brought to his quarantine lab for further study—an aphidlike bug called a psyllid and various caterpillars—aren't voracious enough.

"The insects we've found so far are not exciting from my standpoint," he said. "They don't do a tremendous amount of damage [to buckthorn]."

He's still searching for other candidates, including insects that attack buckthorn found in Asia.

So far, the bugs that have been released in Illinois have been problem-free, but that's not always the case. The most notorious local example of biological control gone haywire is the multicolored Asian lady beetle, a bug brought to the U.S. as early as 1916 and used to control aphids on Southern pecan trees.

With no natural predators in this country—birds don't care for the foul-smelling goo within the beetles—they multiplied quickly, becoming an inescapable annoyance in Illinois and elsewhere.

More serious is the case of an Argentine moth that dines on prickly pear cactus. Australians imported the creature in the 1920s to curb the spread of the cactus, which had been planted as a living fence. The moth worked splendidly, said George Schneider, biological administrator with the Florida Department of Agriculture.

Then other countries started using the moth, and in 1989 it appeared unbidden in the Sunshine State, chewing its way through already rare cactus species. It has since spread west, and agricultural officials fear eco-disaster should it make it to cactus-rich regions in Texas and Mexico.

Researchers are trying to curb its spread by releasing irradiated moths that will mate with the cactus killers to produce sterile offspring, Schneider said.

Experts say biological control will expand as global trade, intentionally or otherwise, brings more invasive plants to the U.S. Some say the risks should be measured against the environmental damage of herbicides and the certain toll of inaction.

"Are you willing to go out every year and cut and cut and spray and spray just to hold the line, or can you look for some solution that lasts for a long time?" said Dave Voegtlin of the Illinois Natural History Survey, which helped to introduce the loosestrife-eating beetle.

"Exotics continue to come in. Our water and soil are just full of them. They're changing the dynamics of our system."