Well, I broke down and bought some NEEM. It's reported in this area to
do a real number on Japanese beetles. Not only does it kill them, it
supposedly acts as a deterrent as well.

I'll report back in the next few days. The JBs have been increasing
daily in quantity and today, they were after the zinnias as well. I
can say this - NEEM seems to distress them as soon as it hits them. I
really hope that this is the final piece in the puzzle. I'm soooo
tired of picking them off my plants. It's fun the first day or two,
but really now...