Emerald Ash Borers and the Purple Triangles

“What are those purple triangles we keep seeing in the trees along the roads?” We’ve had a number of visitors ask this question, and now that the VIC has its own “purple triangle,” I figured the time was ripe to post an explanation.

The purple triangles are traps designed to lure in and capture any emerald ash borers (Agrilus planipennis) that might be in an area. And just what is an emerald ash borer, you might ask. It is a small (half-inch long) metallic green insect that comes to us from Asia via Michigan and it is wreaking havoc on the ash trees of North America.

Recently I wrote a piece on the American elm and its decline thanks to an insect and a fungus. The same thing is happening today with the American beech. But the emerald ash borer (EAB) acts alone. This insect overwinters under the bark of the ash tree (black, green and white ash are all susceptible) and emerges as an adult in the spring. After mating, the female lays her eggs in the crevices of the bark and about ten days later they hatch. The larvae now begin their devastating work, tunneling under the bark, eating as they go. When winter comes, the larvae become dormant, waiting for spring to arrive, at which point they emerge as adults and the cycle begins again.

This may sound innocuous enough, after all aren’t there plenty of other beetles and such that tunnel in trees? Yes, but our native bark boring insects and tunneling beetles have evolved with the trees and environment and have naturally occurring checks and balances in place that keep them under control. When you introduce an exotic like the EAB, there are no predators around to eat it, and the trees (in this case) have no other defenses in place for protection. It’s like letting a child loose in a candy store. Not only has the EAB found a veritable feast of ash trees to slake its hunger, but it is mobile and on the move to find more.

Scientists believe the insect arrived in southeastern Michigan about twelve years ago, probably hiding out in packing materials that arrived from China or other parts of Asia. Its life in its new country went undetected for a long time and was only officially identified in 2002. Since then it has wiped out millions of trees around Detroit alone and has now moved on to Ohio, Maryland, Virginia, Indiana, and parts of Canada. New York is likely to be hit soon, too, as the adult EABs take flight and wing their way to other ash-rich areas, like the Adirondacks.

This is where the purple triangles come into play. The Department of Environmental Conservation (DEC) is hanging these traps throughout parts of the Adirondacks to see if EABs have come across the Blue Line yet. The traps are equipped with a scent packet that is attractive to the insects. If any EABs are in the area, they should be drawn to this lure and when they reach the purple triangle, they will hopefully land on it. This is what the researchers want, for the purple plastic has been painted with sticky glue, and once the insect lands, it is stuck. DEC researchers will then collect the purple triangles and start the task of unsticking and identifying the captured insects. Hopefully they don’t find any, but that could be a double-edged sword. On one hand it could mean there are no EABs in the area (yet), but on the other hand, it could just mean the traps didn’t catch any.

Is there anything that can be done about EAB once they are here? Right now the answer is no. The only things that are showing any interest in eating them are a few woodpeckers, and so far no topical treatments have been developed. If you find your ash trees have been infected, they will likely be dead in one to three years.

How will you know if your trees have an EAB infestation? Detection can be difficult because the decline is gradual. Still, there are some clues you can look for, like dead branches near the top of the tree, leafy shoots growing out of the lower sections of the trunk, and D-shaped holes in the bark (these are the exit holes through which the adults emerge). If you can get a look under the bark of the tree, you will find tunnels that look like a meandering river. If you find these symptoms, call your local extension agent and make plans to have the tree removed.

About the only thing we can do right now is spread the word about EABs. Tell your neighbors, tell your friends. Keep an eye on the health of the ash trees in your neighborhood. If you are going camping, only use the wood available at the campsite – don’t bring your own wood with you. Contrary to rumors, this isn’t a ploy to boost the local economy; any ash wood that is brought into an area could harbor a hidden infestation. Prevention is the best medicine at this point.