My farm is certified organic, so I'm always looking for different ways to control insects. After I had so much trouble with the beetles last year with the bees & my figs, I read somewhere about planting rue around to repel them (it's not an edible herb). I don't want to give it credit for 100% effectiveness, but I followed up this year & it seems to have at least some degree of success. I used pyrethrin (3%) to kill all the jap beetles last year as it is certified organic & kills everything. It has no residual & is photo-sensitive, so if you want the best results, spray in the evening right before dark.
FYI, all the beetles flying around near the lights are male, while the females stay out in the grassy areas for egg-laying capabilities... this goes for Jap beetles, junebugs, fig beetles and the rest. A two-prong approach such as milky spore & spraying is very effective.