The color purple

This afternoon I spotted a purple sort of box kite hanging from some trees in front of a neighbor's farm on Route 926. Was it some kind of a discreet directional marker, like M. Night Shyamalan's "TH" road signs a few years back? An escaped wind sock or recycling bin? I filed it under "odd things."
And then, within the hour, I saw another one along Route 82, near the Kennels, and knew that I had to investigate.
It turns out they are "prism panel traps" for emerald ash borers (Agrilus planipennis), a beetle that kills ash trees and is attracted to the color purple. The beetle's first North American appearance was in Michigan in 1992, and it has moved east from there, appearing in Butler County in Pennsylvania in June 2007.
According to the commonwealth's Department of Conservation and Natural Resources, it's now in Allegheny, Armstrong, Beaver, Butler, Indiana, Lawrence, Mercer, Westmoreland, and Washington Counties in the western part of Pennsylvania and Mifflin and Juniata Counties in the central part.
The traps are being used to monitor the green beetle's movement in the state. They contain a lure and are coated with a sticky substance to capture the beetles, if any show up.
All hardwood firewoods from the western two thirds of Pennsylvania have been quarantined since August 2010 to help slow the spread of the beetle.

(Thanks to "Kennett Paper" editor Fran Maye, who pointed me in the right direction on this one! And also to two Tilda readers for spotting traps along Route 1, near the West Grove exit; and along Route 322, outside of West Chester.)