What are those purple triangular boxes hanging in the trees?

In my ventures out over the last week I have noticed some purple triangular boxes hanging in trees along some back roads in rural Northeast Missouri. My first instinct was to call them swarm traps, but my gut instinct insisted something else.  My curiosity got the best of me and I have done some digging to see what these distinctive looking boxes are all about.
Turns out it's all about EAB, or Emerald Ash Borer (Agrilus planipennis), an insect invader from eastern Russia, northern China, Japan, and Korea.  It's not clear how it got here, but it is likely that it came in ash wood used for stabilizing cargo in ships or for crating consumer products.

It appears to be that the boxes are insect traps of the emerald ash borer, a small, highly destructive wood-boring beetle that's devastating ash trees throughout the northeastern United States.

I contacted the Missouri Department of Conservation to see if my findings were correct, but as luck would have it, today is a state holiday and no one answered my calls. 

I have found two along county roads here in Marion county.  Has anyone spotted them?