Here are some links to documents from the UW to help explain how to fight those little shiny green guys that are eating leaves. They are relatively older, but I think the plan of attack has not changed.

http://wihort.uwex.edu/gardenfacts/X1062.pdf
http://wihort.uwex.edu/gardenfacts/XHT1062.pdf
http://www.uwex.edu/news/2001/7/japanese-beetles-an-invasive-pest

One thing to note: the traps attract MORE BEETLES THAN THEY CATCH. So you should, in all likelihood, NOT be using traps to help manage the population.