Well, they are “traps” for Emerald Ash Borers or EAB’s. This is an insect that came over in shipping from the Orient where these insects live in harmony with their Ash trees, but here the bugs are infesting and killing our Ash trees.
The boxes have no pheremones inside. They do not attract insects the way we normally think of traps attracting them. These are just purple boxes with sticky stuff inside that bugs stick to. If researchers find one EAB then there is a good chance that they’ve been in the canopy for a couple of years at least, and that that county will now be considered an EAB area and there will be rules for handling wood in that community.
Here is a very long video that explains everything you’d ever want to know about EAB’s.