The emerald ash borer, a beetle that got here from Asia in shipping crates and pallets made of infested wood, has killed acres of ash trees since its discovery not far from Detroit in 2002. The bug has spread from Colorado to Georgia, but the tide may be turning. Mother Nature and man have combined to slow the spread of the invasive species, tipping the scales in favor of the ash tree.

The emerald ash borer, it turns out, is good eating. A study published in the journal Biological Invasions documents how the plentiful supply of emerald ash borer larvae and adults fueled a population boom for four species of birds in the Detroit area. The study was based on data from Project FeederWatch, a Cornell Lab of Ornithology project in which volunteers count birds that visit feeders from November through early April.

Areas infested by the emerald ash borer saw increases in the number of downy woodpeckers, hairy woodpeckers, red-bellied woodpeckers and white-breasted nuthatches. All four birds are also cavity nesters and are thought to benefit from the growing number of dead trees.

A red-bellied woodpecker investigates a tree cavity

Photo: qmnonic/Flickr

The predatory pressure of birds eating bugs “is apparently not strong enough to prevent the explosive growth of invading [emerald ash borer] populations,” the study states, “but it does suggest that [emerald ash borer] spread might be faster were it not for the numerical increase of insectivorous birds resulting from the invasion.”

Development of new insecticides may also slow the spread of the emerald ash borer, which was recently discovered in the Atlanta area.

An insecticide called emamectin benzoate – marketed under the label TREE-äge – is being injected into the trunks of still healthy trees. In a study by Michigan State University professors, 100 percent of the beetles that fed on leaves from emamectin benzoate-treated ash trees died. Because the insecticide is injected into the trunk and not sprayed on the leaves, birds, chipmunks and other insects that land in the tree – but don’t feed on it – are not affected, the maker says.

“We haven’t spent the last 10 years sitting on our hands,” said Deborah McCullough, professor of entomology and forestry at Michigan State University told the Duluth News Tribune. “The early treatments often didn’t work very well, or didn’t last very long. … But now we’re seeing very high success with saving treated trees.”

Related on MNN: