Ashes to ashes.

For years the killer stalked Detroit and its suburbs undetected. Now it has unleashed an epidemic that will kill millions. The killer is an insect, the emerald ash borer, and the victims are ash trees.

"The emerald ash borer, without question, is one of the most challenging and difficult plant pests that any state has ever had to deal with," says Sara Linsmeier-Wurfel, a spokesperson for the Michigan Department of Agriculture. "With 700 million ash trees just here in Michigan, we have a lot at stake."

The ash borer is believed to have arrived in Detroit five years ago in wood packing material aboard a cargo ship from Asia. Since then it has killed at least six million ash trees in portions of Michigan and neighboring states and caused the local nursery industry at least $10 million in damages.

The emerald ash borer is only one of the many threats to the nation's forests, which are also being attacked by the Asian longhorn beetle, gypsy moth, beech scale insect, hemlock wooley adelgid and sudden oak death fungus.

These invasions are reminiscent of the Dutch elm blight that arrived in the 1920s and systemically wiped out the American elm tree. But what is strikingly different is the highly organized response to the ash borer.

Since the pest was identified in 2002, a task force of government officials and scientists has worked to survey the spread of the insect, which moves naturally and is spread inadvertently by humans, such as the Michigan nursery owner who admitted shipping contaminated trees to Virginia in violation of a quarantine. He was fined $12,300.

It's too late to stop Dutch elm blight, but the U.S. Department of Agriculture so far has spent $54.3 million to control the ash borer. Because there is no cure, the only solution is to cut down both diseased and healthy trees when the insect is found in an area.

Officials remain upbeat. "We're treating this very seriously and we feel we can get our arms around it and solve it," says Melanie Witt, a spokesperson for the Ohio Department of Agriculture, which also found the ash borer in several counties.

The ultimate solution may be a controlled fire in which every living ash tree within a given zone is destroyed. No one yet has identified how big the firebreak would have to be, but it could easily encompass not only portions of Michigan but areas of Ohio and Indiana. CONTACT: Michigan Emerald Ash Borer Hotline, [phone], www.michigan.gov/mda (click "emerald ash borer").