Based on surveillance, researchers believe more than 95 percent of hemlock adelgids were killed in the northern Appalachians and at least 70 percent died in their southernmost range, Georgia.
At first blush, this appears to be great news, Tobin said. Important trees, including ash, birch and oak, and such vital crops as soybeans, corn and oranges will probably get a break from millions of gnawing mouths.
But invasive bugs are a breed apart. Built to last, they almost never experience extinction.
Female adelgids and cottony cushion scales, for example, are asexual creatures that produce nymphs without copulation. Three generations or more will spring to life between March and October.
As for emerald ash borers, that Minnesota deep freeze affected only a limited number. Chicago also has ash borers, but temperatures there fell only to 17 degrees below zero and likely didn't faze the insects. Minus 20 is the point at which they start to die.
"This problem is not going away," said Rob Venette, a Forest Service research biologist who studied the ash borer.
Winter's blow to the pests is more like a reprieve, said Mike Raupp, a professor of entomology at the University of Maryland, "a little correction" that thinned their ranks and probably will slow them down when warm weather returns.
The cold weather provided a stage for a grand experiment that will help researchers determine if significant numbers of pests can be killed off, making the problems they create more manageable, Raupp said. A decade of study is needed for any definitive conclusions.
Raupp studies the crop-eating brown marmorated stink bug. He said he'd like to be "cautiously optimistic" that winter wiped out huge numbers of them in the mid-Atlantic states, where they have feasted on farm crops for years.