Ash debacle similar to chestnut demise – in Pennsylvania and beyond
Here in Pennsylvania, we are unfortunate to have a window seat overlooking another ecological disaster. One clever headline writer summed it up this way: “Kiss our ash good-bye.”
A comparison between what is now happening to ash trees – they are being wiped out – to the debacle that befell American chestnut trees in the last century – virtually all mature trees of that species were destroyed – is inescapable.
The chestnuts were decimated by a deadly fungus that was accidentally introduced to North America around 1904 when it hitchhiked on Japanese nursery stock.
Ash trees are being killed by a beetle that originally came to North America on wood products from Asia in the early 1990s, but it wasn’t detected until 2002. So far, they’ve been found mostly in the northeastern and northcentral United States, Ontario and Quebec.
Researchers, including several at Penn State, are trying to find a way to enhance natural resistance to the beetles inherent in ash trees, to save the species. Other scientists in the U.S. and Canada are now working to reduce the emerald ash borer population to a level that would allow the trees to survive.
Others are exploring the risks and benefits to culturing and introducing on a large scale a pathogenic fungus that can infect and kill emerald ash borers. And in China, there are tiny parasitic wasps that attack only these beetles. Scientists in Canada reportedly are working toward importing those wasps to attack the ash borers to give the trees a chance to survive.
The emerald ash borer has become the most destructive forest insect to ever invade the U.S. Tens of millions of ash trees have already been killed in forests and other landscapes in 18 states, Ontario and Quebec. Their spread has been slow but steady, and it will continue.
Most adult ash borer beetles stay within a half mile of where they emerge, researchers tell us. Only a small proportion of beetles seem to fly farther. Mature females are probably capable of flying three miles. But the beetles have been moved across longer distances by people who unknowingly transported infested ash trees from nurseries or recently cut logs or firewood.
Beautiful, talented killers
Adult emerald ash borer beetles are beautiful insects and amazingly good at finding, colonizing and killing both green and white ash trees. The beetles use their vision and the mix of chemicals emitted by ash leaves, bark and wood to find their host trees and each other. They are particularly attracted to the blend of compounds given off by stressed or injured ash trees.
Once beetles find an ash tree, they nibble on leaves throughout their three- to six-week life span. Leaf feeding is important for the beetles to mature, scientists say, but it has virtually no effect on the trees. After 15 to 20 days of leaf feeding, the females lay eggs in bark crevices.
The larvae kill ash trees by boring into the bark, then cutting off nutrients coming down the tree from photosynthesis and the water coming up from the roots. They do that by the eating the tissue between the bark and the wood inside.