Emerald ash borer (Photo by USDA)
The clip-clop of horses' hooves, the jangle of harnesses and the hum of buggy wheels are among the familiar sounds that punctuate the usual quiet of northern Indiana's Amish country. The eruption of chain saws and other gas-powered equipment in an area dominated by horse power was the first signal that something was amiss.
“I keep thinking, ‘What a waste,'“ says Jodie Ellis, Purdue Extension exotic species education coordinator, as she watched heavy equipment take down thousands of ash trees on a LaGrange County, Ind., farm in December. All around her lay the turmoil that can happen when an invasive species—even one as tiny as the emerald ash borer —breaches Indiana 's borders. “We're not talking about losing a few ash trees,” she says. “If emerald ash borer really gets out of control, we're talking about the annihilation of an entire species.”
First found near Detroit three years ago, the emerald ash borer infestation quickly spread south throughout Michigan . Federal and state officials tried to slow the insect's cross-country search-and-destroy tactics by cutting down all the ash trees in its path, the only known way to slow its advance. Despite the eradication program, the insect was found in Ohio in 2003 and in Indiana in early 2004, just a few months later. It's difficult to know exactly where the emerald ash borer is at any given moment, because it takes from three to five years for trees to start dying—making quarantining that much harder.
The beetles have destroyed 6 million ash trees in Michigan and thousands more in Ohio. In Indiana, some 24,000 ash trees in LaGrange and Steuben counties will have to be cut down and destroyed by June. Economic losses run into the millions.
The emerald ash borer is just one example of a widening array of invasive species—insects, weeds and diseases—that aren't native to the United States. They often crowd out or kill native plants and insects, wreaking havoc on ecosystems. They range from nuisances, like the Asian lady beetle, to devastating killers, like the emerald ash borer. A National Agricultural Library Web site says that foreign pests cost the United States more than $100 billion each year.
Most of these costs stem from controlling or eradicating infestations, which is, at best, a difficult task. “Our native species co-evolved, so they have natural resistance to each other,” Ellis says. “With invasive species, there's no resistance. They just go wild.”
Invasive species often travel to this country on boats and airplanes in wood packing material and shipping ballast or even in the pressurized cabin of a passenger airplane. “The huge volume of world trade puts our natural resources at risk,” Ellis says.
Once an invasive species arrives on U.S. soil, it can spread by a variety of methods. “The emerald ash borer infestation in Indiana probably happened because someone moved infested ash products,” Ellis says. “More than likely it occurred when firewood or nursery stock was moved.”
Firewood makes it easy for insects to hitch a ride. Campers and hunters unknowingly bring infested firewood with them. If they don't use all the wood, they leave it for the next person to burn. The longer the wood remains, the greater the likelihood that insect larvae will emerge and infect nearby trees.