One application of Grubex last April greatly reduced the jb population in our yard.
Grubex is a dry chemical which you apply like lawn fertilizer

You would have to treat more than just your peonies including all of your neighbors properties to reduce the number of JB. The ones you see flying are not just from the ground surrounding your peonies. Or at least that is how I am reading your post.

Apply Grubex to your entire yard.
Jbs lay their eggs in your lawn; eggs hatch into white larvae which feed on roots of grass during winter and spring, then morph into flying form in midsummer and feed on everyting in sight.

Beetle traps don't work!They only attract your neighbors beetles.I have thousands of these beetles trust me.There isn't to much that I have been able to do they destroy my roses every year but my peonies are done flowering when the beetles arrive.I hand collect them with a bucket of soap and water every evening but they still come!trust me get rid of the traps they can sense those traps from a long distance.