ANN ARBOR, Mich. — A number of odd-looking purple structures have shown up recently in a field near I-94 on the south side of Ann Arbor, Mich. They are rough, box-like structures stuck on a pole, and their purpose is to catch the Emerald Ash Borer (EAB), a bug that’s destroyed millions of ash trees in the Midwest.

“We’re trying a couple of different compounds to lure beetles,” said Deb McCullough, a professor of entomology at Michigan State University (MSU). “What we’re trying to do is find a trap-and-lure system.”

A sticky material is applied to the outside of the boxes, and it’s hoped that the beetles will be attracted to whatever the lure happens to be.

The experiment involves applying compounds of ash foliage, ash bark, ash wood or some combination of these. Some traps don’t have any lure other than the color purple.

“We’ve consistently found purple to be more attractive” to the ash borer, said David Cappaert, an entomologist based in Ann Arbor who’s also working on the project.

The ultimate hope for these traps is that they will be a more effective, less expensive way of assessing the presence of EAB in a given area. Currently the method used is tree girdling, which involves cutting into the tree in hopes of finding the insect.

Finding an effective trap-and-lure system is the “holy grail” of EAB research, McCullough said.

Some traps have been made rough because ash borer females like to lay their eggs on rough surfaces. The traps are checked once a week. According to Cappaert, 6-8 beetles on average are found on each trap every week. The presence of EAB peaks around the beginning of July, and trails off in August.

McCullough is working on the experiment with Therese Poland, a forest entomologist at the USDA who specializes in working on chemical compounds to find better ash borer lures.

The EAB has the potential to wipe out more than 700 million ash trees in Michigan. Since 2002, it’s killed more than 10 million ash trees in southeastern Michigan alone.

For more information, go to www.emeraldashborer.info