Purple Boxes in Trees

You may drive along this summer and see what looks like a purple triangular box hanging in a tree.  It is not a crashed kite, but an insect trap for detecting the presence of Emerald Ash Borer, an exotic insect that is threatening our native ash trees.

Emerald ash borer was introduced into Michigan from Asia in 2002, probably hitchhiking on wooden pallets.  From there is has been steadily moving south towards us, leaving thousands of dead ash trees in its wake.  It has been detected in northern Kentucky and Virginia, and also found last year near Knoxville.  As a result, all three states are setting out traps to monitor the spread of the insect pest.  Cumberland Gap National Park also has a trapping program, particularly around high use camping and picnic areas.

The traps are purple because the insect family that emerald ash borer belongs to is attracted to reds and purple.  The traps have a very sticky non-toxic glue painted on the inside of the box to trap the borer if it’s around.  The traps are baited with an oil from the Manuka tree, which is similar to compounds given off by an ash tree in stress, to which newly hatched adult borers are attracted.  The traps are put out in the Spring and monitored all summer.

Seeing a trap does not mean emerald ash borers are present, it just means government agencies are monitoring their potential spread.  That’s the problem with these bugs.  They spread real easy through the transportation of ash wood over long distances, either in sawlogs or firewood.  That’s probably how they jumped from Ohio to Knoxville so quickly.  There is a national campaign ongoing to educate campers not to bring firewood with them, but buy it locally where they are staying.  And there are bans on transporting ash sawlogs out of infested areas.

The presence of the emerald ash borer typically goes undetected until the trees show symptoms of being infested – usually the upper third of a tree will thin and then die back. This is usually followed by a large number of shoots or branches arising below the dead portions of the trunk. The only way to eliminate the emerald ash borer is to cut down infected trees and burn them, as there is currently no known effective pesticide or other treatment.

There are several species of ash in our area, the most common being white and green ash.  It is a valued wood for both its strength and elasticity, and widely used for making archery bows and tool handles.  The loss of any native tree species is disruptive to forest health, so this is an unfortunate event.

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