Nearly out of ash, borer nibbles tree kin

Bad news in the bug department: The emerald ash borer, a tiny, glitter-green insect from China expected to kill virtually all the ash trees in the eastern United States — unless they are treated with expensive chemicals — appears to have a new target.

The U.S. Department of Agriculture confirmed that the borer had attacked the white fringe tree, which is in the same family as not only the ash but also forsythia and lilac.

Experts don’t know quite what to make of the find yet, other than that it is worrisome.

“This is bringing up more questions than answers,” said Tom Tiddens, supervisor of plant health care at the Chicago Botanic Garden, which is part of a “sentinel plant network” that monitors pests and pathogens.

It also has 42 “beautiful” fringe trees to fret over.

Will the half-inch insect be a major fringe tree pest, or a minor one? Will it kill fringe trees, as it does ashes, or just damage them?

Maybe the insect was merely taste-testing a close relative of the ash because, by now, so few ash trees are left alive in Ohio. That’s where the discovery was made by a college biology professor on a walk. He passed a fringe tree and decided to examine it. Bingo.

As Tiddens put it, “If the buffet is crowded at the primerib station, it seems logical that the meat loaf station may get some visits.”

Or, much scarier: Is the insect adapting?

“I think the finding has some significance,” Tiddens said, adding that researchers have wondered for years what would happen after the borer swept through an area, killing all but a few ash trees. “It makes sense they would begin feeding on other stuff in the same family.”

The recent discovery showed that the insect’s attack on the fringe tree wasn’t brief. It completed its life cycle on the tree. Adults laid eggs, which hatched into larvae, which pupated and re-emerged through D-shaped holes as adults.

The emerald ash borer — one of many borers that attack trees — has been chomping its way south and east from Detroit, where it was discovered in 2002. It is believed to have entered the Detroit port on wooden packing crates.

The borer lays its eggs on the bark of ashes. Eventually, the larvae girdle the tree, cutting the flow of nutrients and killing it.

To Kay Havens, director of plant conservation science at the Chicago Botanic Garden, the emerald ash borer’s seeming dietary divergence represents a cautionary tale about biocontrol, a common conservation practice. In addition to the insects inadvertently carried into the United States are those introduced intentionally, often in an effort to control invasive plants. Researchers find an insect that feeds on the plant in its native range and, after testing to ensure it won’t eat anything else in this country, release it here.

But as now is feared with the emerald ash borer, Havens said, “it happens commonly that insects eat things that we don’t expect them to eat at first.”